The Bourke Engine
The Bourke Engine
(OP)
Okay, kids, here's your assigment: To learn all about the Bourke Engine.
Go visit this website and watch the animation;
http://bourke-engine.com/ani.htm
Supposedly this engine has superior fuel economy and emissions characteristics. As far as I can tell, it is a two stroke engine. Instead of using crankcase scavenging, it uses the lower portion of the cylinder to pump the air necessary for charging the combustion chamber.
It is also claimed that the "Balanced Precision Reverse Cam Effect Roller Crankshaft" did good things too, although from the animation it looks to me that it just results in the piston spending more time at TDC and BDC, and I'm not sure the advantage of that. It apparently is also known as a "Scotch Yoke." The engine is also supposedly "self supercharging."
It is also claimed that the exhaust gas temperature is 190 to 240 deg F, the compression ratio varies from 8:1 to 20:1, and that the air/fuel ratio is 30:1 to 50:1.
I have spent some time looking at the animation, and while I would believe the engine would run, I just don't see how it is "self supercharging", I don't see the advantage of the "Scotch Yoke", and I don't quite understand how it would operate with a 30:1 to 50:1 fuel/air ratio.
If you could get ignition at an air/fuel ratio of 50:1 I could understand why the exhaust gas temperature would be quite low. In addition, the combustion temperature at an A/F ratio of 50:1 would be quite low, which would explain low nitric oxide production, and the PM's might be low by virtue of the excess oxygen present in such a lean condition. But it looks to me that the power density of such an engine would be absymal.
More information on the engine can be found at:
http://www.constant-pressure.com/Home.htm
I must also confess that I don't quite see how this would be a "constant pressure" engine, since it looks to me closer to a "constant volume" engine.
An interesting and somewhat different view of the history of the Bourke Engine can be found at:
http://www.niquette.com/books/sophmag/bourke.htm
Does anybody have any insight about this that I am missing?
Go visit this website and watch the animation;
http://bourke-engine.com/ani.htm
Supposedly this engine has superior fuel economy and emissions characteristics. As far as I can tell, it is a two stroke engine. Instead of using crankcase scavenging, it uses the lower portion of the cylinder to pump the air necessary for charging the combustion chamber.
It is also claimed that the "Balanced Precision Reverse Cam Effect Roller Crankshaft" did good things too, although from the animation it looks to me that it just results in the piston spending more time at TDC and BDC, and I'm not sure the advantage of that. It apparently is also known as a "Scotch Yoke." The engine is also supposedly "self supercharging."
It is also claimed that the exhaust gas temperature is 190 to 240 deg F, the compression ratio varies from 8:1 to 20:1, and that the air/fuel ratio is 30:1 to 50:1.
I have spent some time looking at the animation, and while I would believe the engine would run, I just don't see how it is "self supercharging", I don't see the advantage of the "Scotch Yoke", and I don't quite understand how it would operate with a 30:1 to 50:1 fuel/air ratio.
If you could get ignition at an air/fuel ratio of 50:1 I could understand why the exhaust gas temperature would be quite low. In addition, the combustion temperature at an A/F ratio of 50:1 would be quite low, which would explain low nitric oxide production, and the PM's might be low by virtue of the excess oxygen present in such a lean condition. But it looks to me that the power density of such an engine would be absymal.
More information on the engine can be found at:
http://www.constant-pressure.com/Home.htm
I must also confess that I don't quite see how this would be a "constant pressure" engine, since it looks to me closer to a "constant volume" engine.
An interesting and somewhat different view of the history of the Bourke Engine can be found at:
http://www.niquette.com/books/sophmag/bourke.htm
Does anybody have any insight about this that I am missing?





RE: The Bourke Engine
Self supercharging is a misnomer - they are really self scavenging engines. Nice bit of design, but I'm not sure why it should have higher sfc than most engines. A 2-stroke diesel, now theres an engine to hanker after - especially if it is matched to a turbo for scavenging.
This unit will still have the old problem of allowing the last bit of exhaust pressure to escape untapped. At first I wondered if the Bourke cycle was a piston brayton cycle. This would be very efficient, since the expansion could be greater than compression. Cool exhaust would also result. I think these units just use the coolant to keep the whole combustion cycle at a controlled temperature.
The scotch yoke may wear prematurely too. I prefer the epicycloidal mechanism (rotary engines are one example), although this would require an X-4 config. There have been some nice demos of this, but I'm not aware of any actual engines.
I'm interested to hear a thermodynamic explanation of why this engine is meant to be so good though!
Mart
RE: The Bourke Engine
Mart
RE: The Bourke Engine
Graviman, Detroit Diesel in the USA built 2 cycle diesels for years, and still builds them for non automotive applications.
If you are hankering for one, the junkyards are full of them, and a few of us who have old motorcoach size busses to deal with still have to endure them. And, the latest series, the 92 series (displacement per cylinder, not a year model) was turbo'd and aftercooled, as were some of the older 71's.
Since it still has to have a roots blower to move air to crank, as well as operate when the turbo is not spooled up, the blower can be an impediment to the turbo, unless the "freight truck" option is used, which is basically a by-pass port which diverts turbo air around the blower, which, of course, is volume limited, and straight into the airboxes.
This Bourke engine is interesting. Thanks for the link, SBBlue.
rmw
RE: The Bourke Engine
Must admit, I'm very impressed with the engineering in DD engines. Guess they've tried everything...
Mart
RE: The Bourke Engine
I only wish I had been as right about everything in life as I was that one. If I were to go back into the trucking industry, (God forbid) I would only go with DDA, (Detroit Diesel Allison.
They knew enough to start over with a clean sheet of paper, and abandon the two cycle concept.
rmw
RE: The Bourke Engine
Yup! Waiting to see what Tier4 emissions standard brings...
"If I were to go back into the trucking industry, (God forbid) I would only go with DDA, (Detroit Diesel Allison)."
Both seem to know their stuff very well.
Mart
RE: The Bourke Engine
Have a look at http://www.topolino.demon.co.uk/ts3.htm for a description.
They wee also fitted in some smaller coaches/buses.
The sound these made was something else.
RE: The Bourke Engine
Mart
RE: The Bourke Engine
Seems that they were very economical engines for their time and many of them found their way into boats.
I believe that this design of this engine was heavily inspired by an earlier German design (Sultzer). - feel free to correct me if I'm wrong.
RE: The Bourke Engine
RE: The Bourke Engine
RE: The Bourke Engine
When you talk about "lean combustion" -- just how lean are you talking?
And why should the exhaust gas temperature be any lower than for a normal two-stroke engine?
RE: The Bourke Engine
People are working on NOx traps, but they aren't easy.
Am I right in thinking that the underside of each piston acts as a compressor for the opposing combustion chamber? or does each piston compress its own charge?
Balance wise, as shown, the two cylinder is going to be a bit of a basket case. Increasing the weight of the counterweights will get rid of the first order in the axis of piston movement, at the expense of causing a vertical vibration. A flat 8 would be nicely balanced.
A twin crankshaft version of this would be interesting, as it would eleimnate the balance problem, and the thermal losses through two cylinder heads.
Are you going to measure the fuel consumption soon?
Cheers
Greg Locock
RE: The Bourke Engine
Am I right in thinking that the underside of each piston acts as a compressor for the opposing combustion chamber? or does each piston compress its own charge?
CC:
My interpretation of the pictures was that each piston underside was acting as a compressor for its own charge. That way the pressure is available when it is needed (large cylinder volume).
If a piston underside compressed for the opposing piston, the pressure would be available while the other was firing which is not much use.
I have seen another engine where the backstroke of the piston is used to supercharge the intake. I was going to say 'so its nothing new', but the Bourke engine predates the alternative engine I have seen, and the Bourke is quite old. Maybe I should say 'it might have been new'!
RE: The Bourke Engine
Oxides of nitrogen are avoided by not being produced in the first place. Combustion chamber temperature is lower than that needed to produce NOx.
F/A ratio as lean as 24/1. Excess air.
Low E.G.T is the result of the expansion of the spent charge for a longer time in the cylinder due to the faster burn rate of the charge. Charges are detonated, producing a flame rate of 5000'/sec., whereas a conventional burn rate is around 150'/sec. Expansion causes cooling. Bourke allows more time for this to happen. Bourkes will not "ping" under detonation, due to zero side load component on the piston skirt. All forces are to center and always compressional.
Each cylinder being tuned carefully, a "null" is achieved where each pulse is cancelled by an equal and opposite pulse. Balance is achieved by an exchange of momentum. Bourke uses the destructive detonations to cancel eachother out. Tuning for this null is where most other Bourke experimenters fail. I developed a simple method to show which cylinder is out of phase. Please view the running video posted on
<http://bourkeengine.net>
Viewing the running engine should convince the skeptics that Bourke's "100% dynamic balance" is a fact. Previous researchers' failings have muddied the waters for the Bourke design in this area. They simply failed to find the "null".
Fuel consumption is lower than anything currently on the market. They can be set-up to use almost any fuel, as long as it is 63 octane or less. Remember, we are trying to induce a timed detonation. Currently, fuel is "doctored" to suppress detonation and keep the burn rate within limits.
Russ Bourke's work is "old", but was never fully understood. Careful examination of each function will lead ti insight as to why it does combustion to the higher order. Bourke let's us use higher pressures and produces them "earlier" in the cycle.
We all have seen holed pistons. Bourke presents factual answers as to why conventional rods/pistons are "not suited to the task".
I was trained at Embry-Riddle, and hold a commercial pilot ticket.
RE: The Bourke Engine
I'm assuming that the maximum cylinder temperature is less than 2500 deg F, since that is roughly the range where you start havin NO2 issues. Is that correct?
And as far as "more time" for expansion; it appears to me that the longer you stretch out the burn rate the less efficient the engine will become. The idea situation, at least as far as efficiency is concerned, would be for all of the fuel to be combusted just a hair short of top dead center.
RE: The Bourke Engine
I would think that complete combustion, and therefore peak pressure just on TDC would result destructively high pressures, or excessively heavy engine components.
Also, unless the combustion was virtually instantaneous, there would be some efficiency lost to overcome the pressure build up before TDC.
I would think the best efficiency would be obtained if it were possible to ignite the fuel at just before TDC, so there was nil force trying to run backward, then the pressure instantaneously built up to the optimum then the burn rate adjusted proportionally to piston speed so as to maintain that pressure for the longest possible part of the power stroke.
I think optimum pressure might be just below the point where NOx emissions are a problem, or the point where more efficiency is lost to overcome inertia in reciprocating weight than is gained by increasing the maximum cylinder pressure.
Obviously this level of control on burn rate is currently impossible. The only method I envisage to work toward it is by sophisticated control of charge movement in the chamber and or sophisticated control over the phasing of multiple ignition points.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
The two pistons move in the same direction at the same time. Therefore they cannot cancel each others motion. The addition of counterbalance to the crankwebs can be used to cancel out the forces imposed by this, at the expense of introducing out of plane forces equal in magnitude.
Unless I have missed something?
Cheers
Greg Locock
RE: The Bourke Engine
"Also, unless the combustion was virtually instantaneous, there would be some efficiency lost to overcome the pressure build up before TDC."
I guess I'm missing something here. What are you talking about when you mention overcoming the pressure built up before TDC?
"I would think the best efficiency would be obtained if it were possible to ignite the fuel at just before TDC, so there was nil force trying to run backward, then the pressure instantaneously built up to the optimum then the burn rate adjusted proportionally to piston speed so as to maintain that pressure for the longest possible part of the power stroke."
Any heat added to the cylinder past top dead center will be converted into mechanical energy less efficiently than heat introduced right at top dead center. I can run some numbers on this for you, but right now I'm tired.
"I think optimum pressure might be just below the point where NOx emissions are a problem, or the point where more efficiency is lost to overcome inertia in reciprocating weight than is gained by increasing the maximum cylinder pressure."
NOx emissions are much more a function of temperature than pressure. And for engines that have stoichometric combustion (both spark ignition and compression ignition), the peak temperature is fairly well set. This isn't true for HCCI engines, of course.
"Obviously this level of control on burn rate is currently impossible."
Boy, that would be a real good trick!!
RE: The Bourke Engine
heheheeh... probably the same thing I'm missing. At first I thought "oh, this is just a simple terminology thing. Greg is talking about balancing as it relates to mass distribution within the engine, and B30 is talking about... um... well... something else."
RE: The Bourke Engine
I just spent about an hour on a post, and got a page expired message.
I will see if I can find another hour to invest into this at a later date
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
For my previous post, I was missing a lot about this engine, as I must confess I never read all the posts, and as the links seemed to go to sites with technically poor content, I did not spend much time on them.
I have since attempted to rectify this, but after to much research when the quality of the source information is taken into account, I must admit I am still missing a lot, including nearly half a day of my time.
On all the links I visited, I could not make an animation or video work, so I still have not seen the cycle and I am trying to imagine it from the very few drawings an photos of parts
There are minor differences in piston acceleration rates, and this engine has a small advantage in the piston having pure harmonic motion, and certainly no side loading is an advantage, however the pistons on each side travelling the same direction, as Greg points out will be a balancing disaster.
My comments in my previous post are based on petrol and spark ignition as the fuel.
I see no difference between the way fuel would burn in this engine compared to any other 2 or 4 stroke piston engine.
I see no supercharging as the air below the piston is squeezed into the same volume above the piston.
Lean mixture will result in detonation and destroy the piston, unless it is built to diesel standards that withstand detonation.
The only valving I see in the sketches and drawings are piston port type like any modern 2 stroke. As there is no apparent scavenging or supercharging, I don't see how it runs at all, if the cylinder with residual exhaust gas is over atmospheric pressure.
In my previous post I was taking power density rather than thermodynamic efficiency into account, and my views would soften considerably if only TE was being considered, however I expect that all engines must be a compromise between inertia losses from reciprocating weight, thermal efficiency via expansion ratio.
To answer SBBlue's comments directly:-
To have peak pressure by TDC, you must ignite the fuel considerably before TDC unless you have instantaneous combustion. This time to burn generates some pressure well before TDC, and considerable pressure a little before TDC, all of which resists rotation of the engine.
Even if you have detonation, you still need some time for the pressure to build up before TDC so it will be maximised by TDC.
I agree, using prolonged combustion to maintain peak pressure for a longer portion of the power stroke will give higher power density, but very poor conversion of the heat to mechanical pressure, all other things being equal.
Re NOx emissions. I have been taught that lean mixture, high compression and to much advance all lead to NOx emissions. The high compression and/or excessive advance generates more peak pressure, and therefore more heat. In the presence of free oxygen (from lean mixture) and nitrogen, NOx is then formed. I have never seen evidence to the contrary on this point.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
I'm also a bit disappointed by claims of higher thermodynamic efficiency, without any substantiation: can someone please post a link to measurements of BSFC, or any other measurement of efficiency, or even power output, or fuel consumption, or practical application of the motor?
BT
RE: The Bourke Engine
Re NOx emissions. I have been taught that lean mixture, high compression and to much advance all lead to NOx emissions. The high compression and/or excessive advance generates more peak pressure, and therefore more heat. In the presence of free oxygen (from lean mixture) and nitrogen, NOx is then formed. I have never seen evidence to the contrary on this point.
Crystal Clear:
I believe the main cause of NOx is caused thermal Nox coming from these reactions
N² + O => NO + N
N + O² => NO + O
the rate of reaction increasing with the square root of the pressure, and increasing exponentially with temperature, hence the name thermal NOx.
At lower temperatures, (and high pressure) another pair of reactions is involved
N² + O => N²O
N²O + O => NO + NO
In rich mixtures this can happen
CH + N² => NH + CN
NH + O => NO + H
CN + OH => NO + CH
Also, there can be nitrogen in the fuel causing NOx as well as nitrogen in the air causing it.
Reportedly stoichiometric mixtures give the most NOx, but that defies common sense if you look at it like this. In a stoichiometric mixture, oxygen should be largly used up and less should be available for the thermal NOx reactions. (Maybe this is the logic behind Pat's statement. Its not for me to say.)
However if you look at it differently, stoichiometric mixtures should give higher temperatures, and if thermal NOx production is exponentially linked with temperature, then there are reasons for stoichiometric mixtures giving higher thermal NOx than lean mixtures.
With 'fuel in for coolin' it should be clear that rich mixtures reduce thermal NOx, but I don't think that can be extrapolated to conclude that lean mixtures generate more Nox, unless you are in some sort of supercharged race environment where lean might just mean 'a bit rich but less rich than normal'.
Back to the Bourke engine for my next post hopefully.
I like the point about the Bourke engine volumes above and below the piston being the same and therefor there is no supercharging effect. I think I disagree, but I'd have to see the pictures again to check and see if I could argue a case for my opinion.
RE: The Bourke Engine
As far as nitrous oxide being a function of temperature and pressure. . . . .I think what confuses most people is that compression, and therefore increased pressure is accompanied by increased temperature. The higher the compression ratio, the higher the temperature of the compressed gas. The higher the temperature of the compressed gas, the higher the peak temperature at combustion and the higher the NOx production.
However. . . .it is possible, if you split up the compression process and use inter-compressor cooling, to have a pressure that is just as high but a temperature that is much lower. That will result in a lower combustion temperature and hence less NOx output. This is the approach used by Caterpiller in their ACERTs engines (plus some other stuff).
RE: The Bourke Engine
On it's own water injection cannot be justified thermodynamically. When you take into account cooling heat rejection and emissions, maybe it starts to look better. Exhaust temp will still be ~100'C.
Must admit though I still don't really see why it should offer better sfc...
Mart
RE: The Bourke Engine
On the http://bourkeengine.net/home.htm website, the multi-fuel capability of the engine/cycle is cited as "any low grade fuel (diesel, jet fuel/kerosene, home heating oil, brown distillate, ect.)".
I finally got the SolidWorks model to download and run and it depicts an engine which appears to be compression-ignition, as does the animation on http://www.niquette.com/books/sophmag/bourke.htm#s... a compression ignition/diesel cycle then aligns the fuels quoted and the models/animations.
I also managed to finally get the video from http://bourkeengine.net/videoclips.htm to download and run and this clearly shows what appear to be two spark plugs in the finned cylinder head. If these are spark plugs and not glow plugs for preheating, what part do they play in the function of the engine when running on classical low-quality diesel fuels?
RE: The Bourke Engine
There are no hidden weights. Bourke's dynamic balance works exactly as he describes it. I ripped more than one lord mount trying to get the cylinders in sync. All forces are equal and out of phase by exactly 180 degrees. We have a 5000'/sec. explosion divided by 180 gegrees. I know it is counterintuitive, but it works. 100% dynamic balance is achieved. The faster it revs, the smoother it gets. Regular engines can only achieve a compromise.
Bourke claimed top RPM as high as 20K. It cannot "fly apart", because the rod assembly is always being compressed. My design intent was 4000 RPM to power the generator, although I have taken it to 8000, unladen, otherwise my armature would have disintigrated.
There are two plug holes to the combustion chamber. Ignition is used, initially, to bring the engine to proper temperatures before introducing the heavier fuels. My video clearly shows the ignition being cycled on and off with no variation in performance. I was very surprised the first time I saw this happen. The second hole is used for varying the compression, or the introduction of test devices.
Charges are ignited before TDC, where the slow burning carbon element of the fuel is used as a "fuse" to trigger the explosive combination of the hydrogen content and oxygen, (association) just past TDC. All energy is released earliest in the cycle, which is an requirement of the four-cycle formula. At what temp does association occur? It is well below the NOx threshhold. Rapid expansion of the spent charge cools the cylinder. Cylinder walls are not bathed in flame for the period of the stroke.
Please do not confuse my sites with others. We are not in agreement with some of the info on other pages. Mr. Niquette trounces the Bourke Cycle and condems it on the basis of one engine reviewed. With his sophistication, he should know that a valid statistical result requires a population of more than one sampling. He is invited to review my video frame by frame.
Please don't discount this work because you were not patient or computer savvy enough to get our downloads. Yes, they are a little long, but will go a long way in convincing the skeptics that the Bourke Cycle is superior to Diesel. Diesels suffer from "pressure drop", because of the geometry generated by tyhe crank. Bourke is cam based and has a longer dwell at TDC. Longer fixed volume reducing pressure drop. Maximum pressure is developed earliest in the cycle and is coupled with maximum mechanical advantage. Kinetic energy imparted to the rod-yoke assembly is transferred to the cam, as well as compressing and charging the opposite cylinder . Actually, it is doing intake, compression, power, and exhaust with one movement of the rod-yoke assembly.
The graphics are sufficient to give a clear view of the mechanism. The Solid Works animation is the best you will find on the web. If this does not do it for you, get a copy of the "Bourke Engine Documentary", and follow every function. Beware though, you will have to shed most or your established notions of internal combustion theory. Bourke reduces this theory to physical fact. His research is tough to beat. Too heavy for many readers, but still factual.
So, a timed detonation is not impossible to attain, give GOOD mechanics. And, yes, the EGT is lower than anything currently available. The difference between maximum heat produced and EGT is a true indicator of efficiency.
<http://bourke-engine-project.com>
<http://bourkeengine.net>
There are no tricks. Russ Bourke designed a mechanism better suited to take full advantage of the forces mother nature designed into our fuels.
RE: The Bourke Engine
What exactly do you adjust when you're getting the cylinders in sync? The reciprocating assembly shown in your solidworks-generated .avi video is clearly unbalanced, assuming that the reciprocating components have mass. If they're massless, then you're right, it's probably perfectly dynamically balanced. Fyi, gas forces (due to combustion, compression, etc) do not play a role in balancing.
From the site:
emissions: Russell Bourke, the inventor, stated the exhaust components were carbon dioxide and water vapor.
Exhaust Temperature: Russell Bourke, the inventor, stated that matches could be held in the exhaust without igniting.
Do matches burn particularly well in an atmosphere of carbon dioxide and water vapor?
RE: The Bourke Engine
Bourke30, what we'd really like is test results. Fuel consumption, emissions including NOx, power output, airflow, you know, that sort of thing. Disparaging people's computer skills is not going to work, and pretty animations prove very little. Incidentally anyone who can make a 14 Mb file out of a 10 second animation can scarcely boast about computer skills.
Cheers
Greg Locock
RE: The Bourke Engine
Assumptions: 18:1 Compression ratio. Exhaust Temperature: 200 deg F.
The 18:1 compression ratio is given on one of the web sites. I'm guessing on the temperature, since supposedly the exhaust gas isn't hot enough to burn your hands. This would mean that the temperature is somewhere around 120 deg F, since higher temperatures will certainly burn human skin. For calculation purposes I will assume the exhaust gas temperature is 200 deg F, which is high enough to burn you quite well but considerably below the typical diesel or gas exhaust temperature. Note that this comparatively high temperature assumption works in favor of the Bourke engine.
Ambient (80 deg F) air that undergoes a 18:1 compression will have a temperature of 1157 deg F. Gas in a piston that undergoes a 18:1 expansion, winding up with an exhaust temperature of 200 deg F will have a temperature of 1456 deg F at full compression. The difference in temperature between gas at full compression prior to combustion and after combustion allows us to calculate the amount of energy added from the fuel; this turns out to be 60.8 BTUs per pound of air.
Now if we assume a completely adiabatic engine with no friction losses, the efficiency of this engine will be about 68%. But those engines are hard to come by. An engine thermal loss and much more realistic compression and expansion efficiencies of 91% will only have an efficiency of about zero percent. And the 91% efficiencies are considerably better than typical engine efficiencies.
Let's assume, though, that we have some magic engine elixir that takes away all friction and prevents any heat losses, and does have efficiencies of 100%. The energy density will be about 40 BTU/lb air. In comparison, a normal gas engine would be expected to have energy densities of at least 300 and maybe 400 BTUs/lb air.
To put this in perspective, a 350 cubic inch engine might be expected to have a maximal power output of 30 hp instead of 300 hp.
The air/fuel ratio for the engine? 329:1, a tad higher than the stoichometric ratio of 14.55:1 and the typical diesel engine ratio of 30:1.
Color me a little bit skeptical about the engine.
RE: The Bourke Engine
RE: The Bourke Engine
I am not a college educated thermodynamicist. I am a hobbiest, and I know what I see. These engines run smooth and have a very low EGT, period. Fuel consumption and power output appear to be what Bourke predicted, following the curves he published. A two-stroke that doesn't pump-out clouds of blue smoke? Why would anyone do research on that?
RE: The Bourke Engine
This is not some fancy pants theory, this is fundamental physics.
So cut the attitude and give us some test results.
Reasons why it appears to run smoothly in the video.
1) The reciprocating masses may be very small compared with the engine mass.
2) 1 mm of displacement on the block is an engine destroying 40g at 6000 rpm. Do you think you could see 1mm (40 thou) of vibration on that video?
"As far as computer skills, we are all on a learning curve. The content is the issue. " . You were the one who started criticising computer skills.
Cheers
Greg Locock
RE: The Bourke Engine
"I am not a college educated thermodynamicist. I am a hobbiest, and I know what I see. These engines run smooth and have a very low EGT, period."
No problem. Most engineers don't understand thermodynamics well enough to do basic calculations.
I made the assumption of 200 degrees for the exhaust temperature because of the picture of someone holding their hand over the exhaust port. I was assuming that this meant they could hold it there for some time without burning themselves.
Just because heat is not transferred does not mean that an object is not hot. Example: Heat your oven to 500 degrees F. Open it, and stick you hand inside, taking care not to touch any parts of the oven. Even though the temperature of the air in the oven may be 500 deg F, your hand won't burn if you only leave it exposed for a short time.
So. . . . .what is the temperature of the exhaust gas? It's really not all that hard to get a temperature probe that goes to 1800 deg F. Your local electronics store will have one; they shouldn't cost more than perhaps $50. That would settle the question of exhaust gas temperature.
And while you are at it. . .what fuel are you running in the Bourke Engine? What type of ignition to you use? What is your air/fuel ratio? What is your specific calculated power output?
I would be interested in hearing more. . . .
RE: The Bourke Engine
Hobbyists have no place here, so why do we argue with him.
I believe that it is only because of the considerable volume of sound input into this thread from the professional engineers that it has escaped the red flag thus far.
If we wish to preserve the valuable content, it might be an idea to cease arguing the merit of obviously misconceived or fraudulent claims made by hobbies ts.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
I delve into Eng-Tips regularly to see what's going on. I stumbled across these interesting and informative forums about eighteen months ago and I'd like to think I've helped one or two people along the way - I don't contribute or question much unless I am sure of my ground. Otherwise I check in to browse and learn from other people's knowledge and experience.
As a background note, I've been in the automotive industry in the UK for 28 years, virtually all of that time in association with engines, and about 2/3 of that time on fuel delivery systems, gasoline and diesel.
I've found that some 'professionals' sometimes have the strangest notions about the way the internal combustion engine operates and how its support systems need to function in order for the engine to give its best.
I've had the dispiriting experience of working with managers that didn't have the most basic notions of thermal efficiency and heat transfer, and I've worked with other 'professionals' that couldn't read an engineering drawing to save their project.
Before I came to the auto industry I was an apprentice and then a draftsman in the defence industry, where, in retrospect, standards of competance and knowledgability were higher and wages lower (in the UK at least!) - and that statement is in no way critical of any of the contributions made to this thread by the names I recognise as regular contributors to the Engine and Fuel Engineering Forum. I recognise their valuable knowledge base and I think I have personally profited from the other threads they have contributed to.
As many of you will probably know, the engineering education system here in the UK is somewhat different to that in the USA and my academic qualifications are difficult to compare - however, I got my Joint Institutes HNC (Higher National Certificate, awarded by the UK institutes of aeronautical, mechanical and electrical engineers, probably equivalent to a basic US college degree) in Production Engineering at the age of 20 in 1971 and didn't get my University degree in Automotive Engineering until 2000 at the age of 49.
I'm now a Chartered Engineer with the UK Institute of Electrical Engineers - the status recognised as a 'professional' in the UK.
Quote "Please don't discount this work because you were not patient or computer savvy enough to get our downloads".
Whilst I may not be the biggest personal computer whizz about the place, I can usually make them do what I want and I've also put a few together and un-wrecked some as well.
It never ocurred to me to check the file size on the video as I expected a maximum of, say, 4Mb, and a larger file for the SolidWorks animation.
Knowing my home dial-up would take forever anyway, I am guilty of using the Company's facilities. I work for a big company, one of the US giants, and the Internet connection I have is of 'broadband' capability and more, even given the virus scanning that takes place on all downloads - so when the file took almost 15 minutes to download I was surpised. I should have known! Dummy!
If anyone is still reading - here's the point.
Data - that's what this is dicussion is all about. Notions are fine when a project is in it's infancy. Notions from experienced minds are where some of the best designs in engineering have come from. Not all inovative steps are the fruit of dry research.
However, in this case, it looks like academia should now be the place to fully define the benefits, or otherwise, of the combination of fuels, ignition mechanisms and mechanical mechanisms that apparently give this power unit its claimed unique properties and capabilities.
Velocity diagrams of the power conversion components could be a valuable 'next step' in clarifying the power unit's properties.
If this power unit is 'the business' in suitable applications, then the proponents should get a university or research outfit with the right academic and practical background to get interested and research:
- theoretical and actual balance and vibration of a power unit
- comprehensive performance curves (power, torque, coolant and lubricant temperatures, intake and exhauste temps, etc
- durability
- actual exhaust chemistry and fuel economies of a power unit that has a practical power to weight ratio
- etc.
I would never disparage the 'hobbiest' or those companies that are 'out there', you only have to look at some of the work of model aero enthusiasts, and radio and electronics enthusiasts to see how much a combination of knowledge and outright enthusiasm can do and how some of it (especially currently in radio, electronics and computing) can creep back into industry.
I remember the first time I had a drive of an Orbital engine powered car, I wanted one there and then.
But -- if the claims for the Bourke cycle are to be upheld as fact rather than claims with various levels of substantiation, then perhaps a friendly university or interested corporation may be able to help provide the vital links between notions, appearances and full substantiation.
Meanwhile - I'll be off to look for the Bourke Cycle papers to educate myself some more about it's properties.
RE: The Bourke Engine
per patprimmer 8/31:
>>>>Re NOx emissions. I have been taught that lean mixture, high compression and too much advance all lead to NOx emissions. The high compression and/or excessive advance generates more peak pressure, and therefore more heat. In the presence of free oxygen (from lean mixture) and nitrogen, NOx is then formed. I have never seen evidence to the contrary on this point.<<<<
I think there might be some explanation of the low NOx claim if we consider the Bourke engine to be a “knock engine,” or “detonation engine.” I’m pretty sure that’s what it is – how else can you run an 18:1 compression ratio at lean mixture, and start things out with a spark plug? So, I’m gonna posit the thing is a knock engine, or what I think most people would call a homogeneous charge compression ignition (HCCI) engine. Hallmarks of such an engine seem to be, to date, really poor power density, inability to handle much of a range in loads and speeds, and real trouble controlling the moment of combustion (if you’re too rich, you knock really hard, and if you’re too lean, you don’t fire at all). They also tend to run unevenly, and wear and durability are problems due to the sudden impact of detonation.
But there does seem to be at least one redeeming quality – HCCI engines are being found by pretty reputable outfits, across the board, to have really, really low NOx emissions (see below).
I THINK the explanation given is that it's not exactly the heat that leads to NOx, but the duration of peak temperatures. HCCI engines have a very fast "burn" rate, as mentioned earlier in this thread, so the temperature and pressure peaks, although actually higher than in diesel or spark engines, end up not being sustained long enough for NOx to develop. That’s what I’ve heard – does that make any sense?
And if it does, how does that compute with what I'm reading in another thread that running lean makes things really hot? One would think if cylinder walls and piston heads got really hot during HCCI combustion, which I think is usually pretty lean, that high temperatures would be sustained and thus NOx would still be a problem???
http://www.windsorworkshop.ca/downloads/TomRyan.PD...
(p. 6 and p. 19)
http://www.gmrc.org/gmrc/pdf/gmc03/23-HighPowerFou...
(p.14)
http://www.eere.energy.gov/hydrogenandfuelcells/pd...
(p. 5, bottom; p. 11 - end?, my computer's too slow)
http://www-personal.engin.umich.edu/~mswool/public...
(p.2)
RE: The Bourke Engine
I think the higher exhaust temperature when lean, is more an indicator that when rich, there is excess fuel to help cool the charge by latent heat of vaporisation, but when the mixture is optimum for economy, there is no excess fuel to cool the charge, then when leaner still, there is less fuel to burn, thereby generating less heat.
A HCCI engine might meet some of the claims made by the Bourke engine, but there is nothing about the Bourke engine that suggests it is more suitable to HCCI than a convectional crankshaft and connecting rod engine might be.
Regards
pat pprimmer@acay.com.au
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RE: The Bourke Engine
The only thing I can see that gives it an advantage as an HCCI engine over a conventional crank and conrod is that the rigid coupling between the opposed pistons might mean that the compression forces are transmitted directly from the firing cylinder to the compressing cylinder without loading the scotch yoke mechanism. This might be how such a flimsy looking mechanism does not wear out quickly.
Still doesn't make it balanced.
Still haven't seen any power or fuel consumption figures.
Jeff
RE: The Bourke Engine
Somewhere along the way I must have missed the discussion about why the scotch yoke helps this thing. It doesn't seem to me that trading a couple of piston skirts for a scotch yoke helps to reduce friction. The piston motion isn't going to be tremendously different either (sinusoidal vs sinusoidal+higher orders)...
RE: The Bourke Engine
I can't see the advantage of a scotch yoke arrangement, either, unless it does in fact let the piston spend a longer time at TDC. And if it does, what advantage would this provide -- better approximation of constant volume combustion?
Is there any reason not to consider the action of this thing simply that of a standard non-turbocharged, ported 2-stroke, short of the (possibly) HCCI combustion?
And -- what makes this different than a two-cylinder 2-stroke or 4-stroke opposed with a conventional crank setup? Or are conventional opposed engines balanced (firing from both sides simultaneously)?
RE: The Bourke Engine
I believe that the planes that used these old 2-cyl shakers were called Petenpols or something similar. There was also the "penguin?" trainer aircraft.
RE: The Bourke Engine
The data on this site shows exhaust gas temperatures at 700°C while the another site indicates much lower temperatures.
But note: two of the sites apparently reate to the original Bourke engine or to modern manufactured copies while the Constant Pressure Engine site relates to the later version and to R&D on this later version with ongoing development.
(One of the sites is pretty miffed at the third site...)
I am intrigued to see that the engine has sufficient going for it, apparently, that at least two companies are embarked on R&D with plans to manufacture.
It is interesting to note how novel engine ideas are received and there are plenty of examples in these threads. I wonder how well the Wankel Engine compares for novelty to benefit ratio? and how well it would have been received here at a similar level of development.
JMW
www.viscoanalyser.com
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RE: The Bourke Engine
The Bourke engine website mentions that the engine could "...run in super lean detonation mode...". This sounds like it operates like Honda's "active radicals" engine ( the charge autoignites or self-ignites without aid from the spark plug). Honda's engine only operates in "active radicals" mode at relatively light load. Honda's engine is a two-stroke, and it is available to the public in Japan. I don't think that Honda's engine is sold in the US.
The Bourke engine could indeed operate as lean as claimed if it is operating in the same combustion mode as the Honda engine. The Honda engine does have some emissions but the emissions are relatively low. Hence, the claim that the Bouke engine has no emissions is not reasonable.
Power density would be low for any engine operating that lean. So a very large engine would be required to produce a large amount of power.
Their claim of "Fuel Consumption: 1/4 pound or less of fuel per horse power hour " is vague (they don't say what kind of fuel). Assuming that the fuel is gasoline, that would mean that the engine achieves 53 % brake thermal efficiency --- very high (large diesel engines can reach this level of efficiency). This is much higher than the efficiency achieved by the Honda engine, which operates in a similar mode. This makes the claim of "1/4 pound or less of fuel per horse power hour" a bit suspect.
All in all, the website does not seem to me to be very reliable.
RE: The Bourke Engine
JMW
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RE: The Bourke Engine
http://www.constant-pressure.com/RD.htm
"As the piston reaches the bottom of it's [sic] stroke, the exhaust port is uncovered and the remaining gases are exhausted into the atmosphere. The exhaust gas temperature is much lower than normal engines, due to the fact that as the piston is traveling down on the power stroke, the volume in the cylinder in expanding . . ."
Uh??? I think this means that exhaust gas temp is low because the charge has already completed its [there we go] burning while there was a pause at TDC. So no burning as cylinder volume expands, so lower exhaust temps and better emissions (because closer to constant volume combustion) (this might also have something to do with a faster burn rate?).
The above makes sense for the "Vaux" engine, which appears to be identical to the Bourke except perhaps that it is spark instead of HCCI. But by no stretch of the imagination do I understand the free piston claim. It's not a free piston engine as I conceive of it. Maybe only free in the sense that the scotch yoke allows a dwell at TDC instead of being tied to a standard articulated crank setup, with no dwell. I'd love to see the reciprocal motion of the scotch yoke plotted -- it could be that it reduces reciprocal loads by accelerating and decelerating more gradually than a traditional setup.
RE: The Bourke Engine
<http://bourkeengine.net> site.
This forum was listed after searching "Bourke engine", and I thought that adding my experiences with real running models would be helpful. I think we have gone past saying that it "might" run. I have shown that it will run smoothly and produce cooler exhaust temps. Ten units are being prepared for testing by outside labs. I'm afraid that even with certified results, there will still be those who say it cannot run at all. Such is the plight of those of us who see that Russ Bourke was "on" to something about internal combustion that has been avoided since the beginning. If this were not the case, we would not have to "doctor" fuels to keep the burn rate within limits.
Internet postings are a little long, but clarity and quality were more important than download speed. Careful study of the Solid Works animation will reveal a reason for the smallest detail.
If a hobbiest with more successful running Bourke Engine hours than all the others combined is of no importance to this discussion, I will retire to my garage and put some more hours on the 15 Kw generator test bed.
RE: The Bourke Engine
But the combustion and exhaust gas temperature are quite low, and they have quite low particulate matter and nitrous oxides level.
Another characteristic of HCCI engines is ignition control can be quite a challenge.
RE: The Bourke Engine
That is all that was ever asked for.
I did not say your claims were fraudulent, but either misconceived or fraudulent. I will always say that of claims that are not supported by data or evidence. I now withdraw that statement in the light of some evidence.
I agree, there are several advantages to keeping the forces in line, not the least being virtually eliminating side forces on the piston and bore, and also greatly reduced bending forces on the rods, and removal of lateral acceleration and deceleration.
I agree that most of what we hear as knock is piston slap which will be greatly reduced with a Scotch Yolk, but the instantaneous peak loads on the piston crowns will still be very high, unless the power density is very low.
If the piston loads are very high, diesel engine type pistons will be required.
Both Scotch Yolk and conventional con rod engines instantaneously stop the piston at TDC and BDC, but in both cases this is an infinitely short time. Whether one infinitely short time is shorter than another infinitely short time. The rates of acceleration before and after that instant are lowest for the Scotch Yolk, and increase in conventional con rod engines with decrease in rod to stroke ratio, but at reasonable rod ratios, the difference between the piston acceleration rates is of little practical importance.
I still don't see a supercharging effect unless there are valves that don't show in the drawing.
I guess I will once again try to download the Solid Works animation, that is when I am about to leave the computer unattended for an hour or so. Maybe it will become clearer.
I certainly do not want to stifle nor criticise invention, but I certainly like to see claims supported with credible data, logic and evidence.
Regards
pat pprimmer@acay.com.au
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RE: The Bourke Engine
The transition to "cycle" is clearly audible in the "proto" video posted on
<http://bourkeengine.net>
Again, please forgive the long download time. I wanted to preserve as much detail as possible.
During start-up, the familiar two-srtoke "bum-ba-bum-bum" is followed by the distinct "jump" to detonation mode, where the engine smoothes-out and the exhaust pulses are uniform. All exhaust smoke stops. I actually have to lean the fuel screw to get this to happen. I use a Matrix air clutch and variable regulator to engage the motor-generator A.C.and D.C armatures. The engine responds better to fuel flow adjustment than to throttle adjustment. As far as dynamic balance, slight oscillations decrease as RPM increases. This is also clearly visible on the video.
patprimmer
"Both Scotch Yolk and conventional con rod engines instantaneously stop the piston at TDC and BDC, but in both cases this is an infinitely short time. Whether one infinitely short time is shorter than another infinitely short time. The rates of acceleration before and after that instant are lowest for the Scotch Yolk, and increase in conventional con rod engines with decrease in rod to stroke ratio, but at reasonable rod ratios, the difference between the piston acceleration rates is of little practical importance,"
Bourke 30
These "infinately short" times are extremely important. I would use milliseconds per reversal, Since the I/C formula calls for "fixed volume", and since Bourke flame rates exceed 5000'/sec., the additional time at confinement can make a huge difference. Bourke chose the Scotch yoke mechanism for this measurable diffrence, to maintain volume, avoid pressure drop, and provide mechanical advantage during pressure maximum. Mother nature dictates that in order for a reaction to go to completion, it must be violent. Bourke is better positioned to absorb these detonations by virtue of the straight line solid connection between the pistons, provided by the yoke.
For Proto video and Solid Works animation;
<http://bourkeengine.net>
For historical photos and Proto model:
<http://bourke-engine-project.com>
Technical information contained in the "Bourke Engine Documentary", by Lois Bourke and Elwin Coutant, is available elsewhere on the web. Graphs and plots along with many magazine articles and references give good reason to listen to what Bourke preached.
I'd like to thank all of you for the fair hearing.
<roger@rogerrichard.com" TARGET="_blank">http://roger@rogerrichard.com
RE: The Bourke Engine
Can you provide the bore, stroke, and volume over the piston at TDC, then one of the younger whizz kids who still remembers the math or who has the appropriate software, can run the numbers re comparative changes in volume over the piston during the burn time, for a convectional engine of same dimensions with say a 1.5:1 and a 2:1 rod to stroke ratio, as this range should cover most production motors.
A second note. If that is you in the video, who is feeling the exhaust, adjusting the carby and putting your head down near the rotating parts, I would caution you as to the possibility of serious injury if anything goes seriously wrong with this experimental engine while you are so close to the moving and stressed parts.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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RE: The Bourke Engine
Unless I lost a decimal place or 2, a quick calculation says that an engine rotates through 36 deg in a millisecond if the engine is doing 6000 rpm. A millisecond is a long time compared to infinitely short time or instantaneous.
36 deg does involve a significant change in the volume over the piston, and the percentage increase is higher for a high compression engine as the original volume is smaller.
As I say, with actual dimensions this can all be calculated accurately
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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RE: The Bourke Engine
I have what you request on floppy disc- Microsoft spreadsheet. It will be posted as soon as we can get it to our site manager.
Thanks for the heads-up on safety. Early-on it was a little scary, but as I gained confidence that it wasn't going to explode, I got a little closer to it.
RE: The Bourke Engine
Here is my take on the Bourke Engine concept, as shown in the linked website:
1. The high efficiency claim may result from the fact that as a detonation engine, the P-V cycle is the theoretical otto cycle. Since the compression ration is 18:1 and the heat injection is near instantaneous, the peak pressure will far exceed anything seen in a diesel.
2. The total balance results from the crank having a balancer equal to the total piston/con-rod mass. This leaves a vertical component to balance. In the case of the engine shown, the main "scotch yoke" bearing has an offset mass, also equal to the total piston/con-rod mass. Due to contact driven rotation the vertical balance mass effectively moves in a vertical line. An epicycloidal mechanism is suggested as a better solution, however.
3. In order for the balance mechanism above to work, yoke bearing contact against the piston nearer TDC must be maintained. Since the engine runs at high compression ratios, and has 2-stroke detonation combustion, this can be maintained up to higher than expected RPM.
4. The engine is apparently 2-stroke in layout, with yoke mechanism providing a sealed lower chamber. This allows the engine to scavenge effectively, and is sometimes misquoted as supercharging.
5. The ideal fuel for the engine is the subject of debate. The ideal fuel allows the detonation point to be maintained at TDC, regardless of load and rpm.
6. By running very lean, this engine has much of the cooling in the active gas stream. In this way cylinder walls may be kept cool in the same way that a gas turbine combustion chamber temperature is controlled.
7. Since the detonation occurs throughout the mixture near instantaneously, no NOx may form. Since the working fluid is far below stoichiometric throughout the cylinder, there are no regions of high temperature. This gives a very favourable combustion environment for emissions.
Hopefully this (brief) analysis of the evidence presented in this thread, and on the site will rekindle this discussion. I promise not to bit anyone's head off if they don't quite understand any of my points above...
Sincerely,
Mart
RE: The Bourke Engine
Bourke is Otto cycle taken to its' extreme.
The roller cam assembly spins as a flywheel, independent of the rod-yoke assembly. Counterweights correct only for the mass of the journal bearing. It is strobe balanced to 10k by removing small amounts of material from the counterweights.
For every action, there is an equal and opposite reaction. In the case of the Bourke, the action of the rod-yoke assembly (which includes pistons, rings, pins, rods, and yoke plates being one mass), is thrown down the bore, causing the engine casing to want to go in the opposite direction. Within milliseconds, depending on RPM, the opposing cylinder fires, and the rod-yoke assembly is thrown in the oposite direction, causing the casing to try to fly outward. This is why I call it exchange of momentum. The engine casing transfers momentum to the opposite cylinder where it almost instantly reversed, again. The time between reversals is the frequency of vibration. This can only be accomplished if the cylinders are in a straight line, horizontally opposed, common pin. This is why the Bourke gets smoother with RPM increase. Less time between reversals. This dynamic balancing scheme is absolutely elegant, as no percent balance factor is necessary. With a little mental gymnastics, this should become clearer. I got a much better handle on it after I got the proto to fire-up and observed the oscillations. Any misfire translates into shaking and vibration. This pits the Bourke against established practice. It was stated further up in the replies that cylinder pressure has little effect on dynamic balance. Bourke changed the rules. What I have described is visible in the proto video engine start-up.
Bourke is definitely a two-stroke. The scavebge chambers below the pistons induct the charge, which does not have to carry oil for bottom end lubrication, since the bottom end case is sealed. An added benefit is that oil never sees the carbon from combustion and does not get contaminated.
Although the rod assembly is not fixed to the reverse roller cam, I still don't think it can be called a free piston design. The reverse roller cam serves as a PTO, converting the oscillating motion of the rod assembly into rotational motion, and limiting rod travel in case of misfire. The gas dynamic is a fundamental part of the workings, as, apparently, is not the case in conventional articulateds.
There is only so much energy in the inducted charge and Bourke is not reinventing thermodymics. His mechanism converts a larger percentage of this available heat into useful work by eliminating dead strokes and other "power thieves", as he describes it. He is not squeezing more energy from the charges, just more useful work.
Bourke's fuel curve is linear. Fuel demand is determined by load and not RPM, being similar to current demand of an electric motor.
Although I have not tried for the claimed 20k RPM, it appears possible due to the lack of tensile forces. At this level, induction stall would seem a real possibility. My model was intended to do 4K, and induction was sized accordingly, limiting RPM to 8k tops. Larger intake tracts can be installed for more breath. Bourke parts are hard to come by, so the reason for being conservative.
The large cam roller rotates unidirectionally, a round bearing rolling in a circle in a square box. Why the Collins design opted for a square rubbing block is beyond me. Why slide when you can roll? They have also defeated many of the Bourke benefits by going with a conventional four-stroke cycle top end, with its' aditional complexity and expense. One comment called the rod-yoke assembly flimsy. It is adequately sized, constructed, and constrained. Rods are hollow for side wall strength and minimum heat transfer. All torsional moments are borne by the guide bushings. Obviously, minimal mass is beneficial. Less power required to operate the mechanism means more power out.
Even if Bourke were on par with conventional outputs, its' simplicity and relative ease of manufacture makes it an ideal alternative engine candidate. Hopefully, upcoming water brake testing will put hard figures on its' true character. Let the chips fall where they will.
Again, thanks to the forum for allowing me to present the case for Bourke. My goal was to reproduce Bourke's work and get to the bottom of it- one way or the other.
RE: The Bourke Engine
I take it you mean the crank balance by this?
"...the action of the rod-yoke assembly ... is thrown down the bore, causing the engine casing to want to go in the opposite direction."
Hmmm, technically this is actually using the engine as an inertial absorber. I understand your point, but the ideal is that the block remains absolutely static. Put your hand on a Jaguar V12 to see what I mean.
"Any misfire translates into shaking and vibration. This pits the Bourke against established practice."
I read this as the roller cam assy goes out of synch, since it momentarily loses contact. This means it cannot produce the required vertical balance component.
"The scavebge chambers below the pistons induct the charge, which does not have to carry oil for bottom end lubrication, since the bottom end case is sealed"
Yes, I like this feature. It is another reason I personally favour epicycloidal big end 2-strokes...
"The gas dynamic is a fundamental part of the workings, as, apparently, is not the case in conventional articulateds."
Again, I think this is due to the need to keep roller cam in contact with the yoke.
"His mechanism converts a larger percentage of this available heat into useful work by eliminating dead strokes and other "power thieves", as he describes it."
Well, lets just say that it is a high compression ratio otto. Most here will accept that. 4-strokes do suffer some pumping losses, but 2-strokes also suffer scavenging losses.
"Fuel demand is determined by load and not RPM, being similar to current demand of an electric motor."
Basically this means the thing has very good volumetric efficiency across the rpm band. It does not "come on cam" so to speak.
"Although I have not tried for the claimed 20k RPM, it appears possible due to the lack of tensile forces."
Well balanced motorbike racing 2-strokes regularly get 20k...
"The large cam roller rotates unidirectionally, a round bearing rolling in a circle in a square box."
I don't see how it could balance any other way.
"Again, thanks to the forum for allowing me to present the case for Bourke..."
Anyone that has put this much effort into a project, hobbyist or not, will have a great deal of practical experience to offer...
Mart
RE: The Bourke Engine
I don't see how it could balance any other way.
I still don't see how the engine shown could balance this way either... wouldn't the "roller" have to complete one revolution for each engine revolution? Wouldn't this require that the roller diameter be approximately (2/pi) times the stroke of the engine (about 2/3)? In other words, wouldn't the roller radius have to be precisely 2/3.14 the crank radius (instead of ~1/1 as shown)? If the roller diameter is even the tiniest bit too big or too small, then the weights will go "out of sync, right?
Also, for this to work the way you describe, wouldn't the firing pressure halfway through the firing stroke have to be precisely equal to the compression pressure halfway through the compression stroke (so that the roller switches from one side to the other at exactly 1/2 stroke, every single time)? (no inertia load at 1/2 stroke, right?) If it switched a little late or a little early, the roller would skid and the engine would go "out of sync," right?
Don't yokes like these work much better with very little clearance? If you used teeth to "sync" the roller, you could get around roller size problems, but wouldn't that require excessive clearance?
RE: The Bourke Engine
RE: The Bourke Engine
Roger,
How are the piston and rings lubricated?
RE: The Bourke Engine
If the rings seal as well as a convectional engine, they would need lube pretty much as per a normal 2 or 4 stroke, but the piston skirts could survive on significantly less oil as they have minimal side loading.
As the engine would not be so prone losses due to blow-by, maybe the ring seal is not so critical.
The pistons and bores would be cooled to some extent by the incoming charge, so the cooling effect of the oil might not be required.
It only needs compression rings, not oil control rings.
The rings are always square in the bore as the pistons don't rock over top dead centre, this should allow for a very low tension compression ring.
Just maybe, with the right bore material, coating and finish, the right ring material and tension, and very slight leakage past the oil seal, it might just get by.
Just a few random thoughts, not fully considered nor thought through.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
Good point. I assume the cad model takes some liberties with the actual design, but I could be wrong.
"...wouldn't the firing pressure halfway through the firing stroke have to be precisely equal to the compression pressure halfway through the compression stroke...If it switched a little late or a little early, the roller would skid and the engine would go "out of sync," right?"
Yeah, this is why I assume that Bourke30 has had so much trouble getting the thing to balance. I imagine that since the bearing assy acts as a flywheel, the inertia minimises this tendancy to go out of synch.
"If you used teeth to "sync" the roller, you could get around roller size problems, but wouldn't that require excessive clearance?"
Hmmm, I've seen involute teeth designed to work inside epicycloidal mechs. They are "inverted" in form, but are still compact. Don't get me wrong, I still greatly prefer epicycloidal design over this particular yoke mechanism, but am trying to understand the balance claim.
BTW, apologies that I seemed to be having a go at you in particular the other day. It was more frustration that more scoffing seemed to be prevelant than lateral thought, but was not directed at anyone in particular...
Mart
RE: The Bourke Engine
I don't see why you are talking about the roller being synched to the motion. From my viewing of the solid works animation, it is just a cylindrical roller and plays no part in any balancing. It could be replaced with a slide (which would eliminate the single line of contact between the roller and the yoke). The balance masses are on the crank webs and will be synchronised because they are part of the crank. Is there something I am missing here?
Jeff
RE: The Bourke Engine
JMW
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RE: The Bourke Engine
I don't think it is, personally, but I thought I'd go along with the idea and see where it ends up. My current thinking is more along the lines of "could it? how?" than "does it?".
RE: The Bourke Engine
RE: The Bourke Engine
Any pure hydrocarbon or carbohydrate when burnt in the presence of an excess of air will form CO2 and H2O, so long as the temperatures are not high enough to form oxides of nitrogen.
All commercial chemicals contain some level of impurity, and low grades generally implies more impurities, but for fuel might also imply low octane or low energy per unit.
Impurities can form all sorts of by products when burnt.
Common byproducts from impurities in fuels are oxides of sulphur, but they can be a vast array of chemicals depending on what is in the fuel, like residual pesticides in vegetable matter used to produce ethanol for instance.
I have no data at hand, but I would expect that the addition of water might actually raise the octane level of ethanol
Regards
pat pprimmer@acay.com.au
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RE: The Bourke Engine
RE: The Bourke Engine
OK, but there seem to be lots of Bourke engine developments out there. If there is an effective 2xpiston_mass offset crank diam from bearing axis, and bearing/flywheel radius is 2/pi then balance is possible. In the real world for packaging the mass would need to be higher to compensate for reduced distance, since rpm must be precisely matched.
"One of the web sites I referred to ... showed one engine with "teeth"."
Interesting...
"Regarding emissions....."
Basically with detonation, anything that is well mixed with air will combust well. This includes coal dust and even custard powder, hence the occasional food processing plant explosion!
Mart
RE: The Bourke Engine
http://www.devauxengines.com/forum/showthread.php?...
and here is a link to the engine with "teeth"
http://www.powerengine.com/an001masterani1l.htm
JMW
www.viscoanalyser.com
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RE: The Bourke Engine
If you put a ladder on a one foot box, the top of the ladder will lean against the wall one foot higher, ragardless of the incline of the ladder.
If you pull the bottom of a ladder a foot further away from the wall, the top of the ladder will come down a few inches.
As the crankshaft rotates, the piston moves up and down for both of these reasons, both effects being active all the time. But if you think about it a little, around TDC and BDC, the piston rises and falls with noticable bottom of the ladder moving effect. At around 90°, the piston is rising or falling almost completely due to the ladder on a box effect.
Now if we look at the scotch yoke in the Bourke engine, you can see that at TDC and BDC there is no vertical piston movement due to bottom of the ladder moving effect.
I think that should help people to see how the Bourke engine is 'spending longer at TDC'.
Since work equals force times distance, the merits of moving smaller distances with the higher force from the greater pressures don't seem at all clear. At present it looks to me like HCCI similarites would be better explanations of efficiency rather than the idea that the flame front is not chasing the piston down so much.
RE: The Bourke Engine
Me likey!
"and here is a link to the engine with "teeth""
Clever, although lots of friction. I'll stick with epicycloidal mechanisms - 'cos it rolls off the tongue
"But if you think about it a little, around TDC and BDC, the piston rises and falls with noticable bottom of the ladder moving effect"
Nice explanation. Yoke mechanisms avoid the 2nd order piston movement, so piston motion is sinusoidal...
"Since work equals force times distance, the merits of moving smaller distances with the higher force from the greater pressures don't seem at all clear."
In spark ignition engines, and particularly with compression ignition engines the combustion takes time. An increased TDC dwell time helps keep the BMEP pressure higher, since pressure gets higher before the expansion stroke gets really going.
Mart
RE: The Bourke Engine
define "TDC dwell time" as the amount of time that the piston spends within 1% of the stroke of TDC (so within 1.2mm of TDC for a 120mm stroke)
pick a "short" rod / stroke ratio of 1.5:1
TDC dwell is 19.98deg for a conventional configuration
TDC dwell is 22.94deg for a yoke configuration
pick a "long" rod/stroke of 2:1
TDC dwell is 20.54deg for a conventional configuration
TDC dwell is 22.94deg for a yoke configuration
RE: The Bourke Engine
Mart
RE: The Bourke Engine
I'm saying that the maximum additional "tdc dwell time" is about 13%, depending on how you define dwell.
RE: The Bourke Engine
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
Well worth having for high rpm engine then. Admitedly it will have a reduced efficiency benefit in a detonation engine, since combustion time is "small".
Does anyone have any info on detonation times, or even a P-V curve? I'm curious how it compares with S.I. and C.I.
Mart
RE: The Bourke Engine
B/S 74.5 x 68 B/S 74.5x 68 upper B/S 54x22
TDC 4 stroke TDC 6 cycle Beare
30.4cc 30.4cc combustion chamber volume
3.04E-05 3.04E-05 360 TDC
3.07E-05 3.06E-05
3.10E-05 3.09E-05
3.14E-05 3.12E-05
3.18E-05 3.16E-05
3.23E-05 3.21E-05
3.28E-05 3.26E-05
3.34E-05 3.32E-05
3.40E-05 3.38E-05
3.47E-05 3.45E-05
3.55E-05 3.52E-05
3.63E-05 3.60E-05
3.71E-05 3.68E-05
3.80E-05 3.77E-05
3.90E-05 3.87E-05
4.00E-05 3.97E-05
4.11E-05 4.08E-05
4.22E-05 4.19E-05
4.34E-05 4.31E-05
4.46E-05 4.43E-05
4.58E-05 4.56E-05
4.72E-05 4.69E-05
4.85E-05 4.83E-05
4.99E-05 4.97E-05
5.14E-05 5.11E-05
5.29E-05 5.27E-05
5.44E-05 5.42E-05
5.60E-05 5.59E-05
5.77E-05 5.75E-05
5.94E-05 5.92E-05
6.11E-05 6.10E-05
6.29E-05 6.28E-05
6.47E-05 6.46E-05
6.65E-05 6.65E-05 393 degrees ATDC
The rate of change in volume of the combustion chamber of the beare head is less than the rate of change of the fourstroke. with the upper piston retarded in its relationship by 20 degrees.
malbeare http://www.jack-brabham-engines.com/
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
RE: The Bourke Engine
Mart
RE: The Bourke Engine
you are right in that you get very high volumetric efficiency with very low pumping losses especially at low rpm low throttle settings. we setup a good stratification with the ignitable mixture swirling towards the outside close to the spark plugs in the combustion chamber side wall.
The head actually produces power this is fundimental to a gain in mechanical efficiency aprox 8 to 10%.
The rate of change in combustion chamber volume is less than a fourstroke during combustion so that it is closer to the ideal of constant volume during combustion. but the rate of change in volume during the rest of the expansion stroke is faster and larger than a fourstroke. so there is a gain similar to the atkins or miller cycle.
Coupled with our air assisted fuel injector that produces dropplet sizes of 5 micron and the ability to induce a premix of 20% intake volume thruogh the injector. we efectivly have all the advantages of direct injection without the nozzle being in the combustion chamber and subject to cylinder temps and pressure.
It is still very much work in progress so I cannot diclose all . But I hope this gives you an overview of the advantages
http://www.jack-brabham-engines.com/
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
RE: The Bourke Engine
OK, so the flame starts from outside in? Does this produce any flame quenching?
"The rate of change in combustion chamber volume is less than a fourstroke during combustion so that it is closer to the ideal of constant volume during combustion."
And you avoid cams and valves...
"Coupled with our air assisted fuel injector that produces dropplet sizes of 5 micron and the ability to induce a premix of 20% intake volume thruogh the injector."
This alone is a nice line of endeavor. Can this be fitted to other engines, or is it part of the Beare package?
Mart
RE: The Bourke Engine
Can anybody measure the fuel consumption of their engine, under a load (say, a generator operating a bank of light bulbs) and report it?
If there is some confusion about how to rig such a test, post your query here and we can all kick some ideas around.
RE: The Bourke Engine
nick
RE: The Bourke Engine
RE: The Bourke Engine
30 159 216 2000 35.8%
35 138 184 2500 33%
40 107 134 3000 25.2%
45 89 101 3500 13%
YAMAHA TT 500cc
Test by Malcolm Beare, Elliot Munro, Grant Guy, July 1995
The dyno used was an old motorbike dyno with the rear wheel driving a large fan with a speed readout dial. The throttle was opend enough to maintain the designated speed.
The sixstroke head was designed to as closely match the fourstroke as possible compression ratio , valve timing , port sizes.
The sixstroke would run happily at lower revs(1000) than the fourstroke in 5th gear. The fourstroke would pull 4000 RPM at full throttle the sixstroke 3500.I think that the maximum horsepower is in the region of 18 HP for the sixstroke and 22HP for the fourstroke
Same gearing same carburetor.
Fuel was gravity fed to the carb from a long clear tube with two level marks to indicate 100cc
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare
RE: The Bourke Engine
THANK YOU! That's a nice, brief, concise test report. It's nice to see somebody making the effort, taking the time, measuring some data, and having the guts to report it.
Now - I'm impressed by the numbers, but I'm not sure if we aren't looking at two different engine "sizes"... i.e. I wonder what happens when each engine is run at near-stall conditions. I'd expect the 4-banger is actually giving more peak h.p. and probably has a higher top end. Having a way to modulate and measure the output power, to run the motor up against its stall limit, would allow a better comparison than just the run time at a fixed power setting. What I'm saying is that the BSFC of the 6-stroke motor may or may not be better than the 4-banger at reduced throttle settings, without measuring power we just don't know (but your numbers certainly look good, and make me curious to find out!) Could you not couple the motor's output shaft to a generator, or a brake, and vary the load to map the power-specific fuel consumption?
RE: The Bourke Engine
Would you like to start a new thread on this as it is technically off subject, not being a Bourke engine, but more to the point, this thread has become VERY long and it takes quite a time for the page to load and allow me to scroll to the end.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: The Bourke Engine
The laod or power output is the same for each engine at the designated speed because the fan is absorbing the same X horspower or requires the same torque to turn it at the same speed . only the throttle settings must have been different.
It would be a good debating point whether the reed valves alone accounted for the superior performance by not allowing any spittback and therefore making carburation cleaner and more precise. Or how much the mechanical construction added to the gain in fuel efficiency. I suspect a little of both.
I have come to the conclusion that to obtain good gas flow at higher RPM the a combination of reed and rotary disk is needed on the intake. Reeds tend to fall over above 6000 and flutter.
If you look at the change in volumes for each engine then the 4 stroke is 500cc for each stroke , but the sixstroke is smaller on the intake and larger on the compression and expansion but smaller again on the exhaust. This varies depending on the phasing relationship between the upper and lower main crankshaft.
At 2000 rpm the 4 banger is at its stall limit in 5 gear
The practical result is that on the road the sixstroke would save fuel.
http://www.jack-brabham-engines.com/
A tidy mind not intelligent as it ignors the random opportunities of total chaos. Thats my excuse anyway
Malbeare