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btu's per hp

btu's per hp

btu's per hp

(OP)
Is there a formula for figuring out how many btu's are consumed per horsepower. In other words, gas has 125,000 btu's per gallon, theoretically at 100 percent effiency how far would this take a 3500 vehicle rated at 200 hp. I realize friction among many other varibles come into play, just looking for ballpark, thanks

RE: btu's per hp

Your biggest loss is thermodynamic efficiency.

About 1/3 the total heat released by the fuel goes to the cooling system, about 1/3 to the flywheel and about 1/3 out the exhaust pipe.

Friction is relatively small with most being in the rings.

There is also a bit through windage in the crankcase and through driving the oil pump.

A little is lost in pumping air.

A little is lost to accelerating and decelerating reciprocating weight.

Other very variable losses are through ancillaries like alternator, power steering, air conditioning, water pump etc.

All of the above vary a lot with different engine size and fuel type.

Also, comparable products from various manufacturers vary to a lesser degree  from individual design details.

For comparable engines, the main factors effecting thermodynamic efficiency are compression ratio, expansion ratio, cam timing, surface area to volume ratio of the surfaces contacting the charge during the compression and power strokes, coolant temperature and conductivity of the materials.

Regards

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: btu's per hp

high effiency units run 7500 LHV (lower heating value) BTU/hp-hr older engines 10,000 btu/hr-hr.  Turbines run 9000 to 13000 btu/HP-hr.

A 3500 lb vehicle would only use 200Hp runnig at 150+ miles/hr if it has a low drag coefficient.

200HP is 1,500,000 BTU/hr  If Gasoline has 125,000 BTU/gal, 12 gallons/hr.  In 1 hour, you could travel 150 miles on 12 gallons, 12+ miles/gallon.

RE: btu's per hp

But, a 3500 lb vehicle at 65 mph with a drag CF of around .32 on level ground may only require 40 bhp, and that is through wind resistance and to a lesser extent road friction.  The rest is lost through pumping losses and engine thermodynamic loss (re: Patprimmer).

A 120 cid engine at WOT will pump about the same theoretic CFM as a 350 cid engine at 1/3 throttle opening, with only half the internal friction.

Just guessing the vehicle mileage through fuel BTU's is only a small fraction of the total equation.

Franz

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: btu's per hp

(OP)
Thanks guys for the replys, I see I was a little brief in my question. dcasto answer seems to be based on me using a substained 200 hp (which is how I ask the question) per gallon of gas. This would have most four cylinders and some six cylinders at wot, so I can see why only 12 mpg. franzh answer is closer to what I was really asking.

  My real question is, is it mathematically possible for the likes of Charles Pogue, Fisher, Smokey Yunich to get over 100mpg. Is there enough energy in a gallon of gas to carry a vehicle that distance?

RE: btu's per hp

Smokey Yunick's nickname of Smokey came from two sources:  One of which was his everpresent cigar, the other from what he blew up others nethers!  He was indeed a genius and his 100 mpg Chevy of the 1980's was pretty ingenious but never worked the same way twice.  I saw it during one of my SAE workshops in Daytona in the late 80's, all it was is a sawed in half 2.8 liter GM V-6 (3 cyls), a turbocharger, and a real small carburetor with superheated gasoline (he called the process a homogenizer!).

Reality:
For a conventional vehicle to get 100 mpg, it would barely run over idle, a real tiny engine (swept area), stripped of all inertia bound weight, coasting downhill with a strong tail wind, and a huge flywheel.  I don’t really see how.  

Pogue and the Fish carburetor guru groups are nothing but charlatans and never proven outside of questionable unsubstantiated non verifiable third party anecdotes.

They were never bought out by the oil companies, the government didn’t "lose the patents", they didn’t magically "disappear".  Take one of these units plus their most vocal advocate and install it under recognized emission laboratory conditions with third party non-biased witnesses and lets see the actual results.

Our engines today are approaching their limits for thermal efficiency, dont expect any significant improvements over what they are currently.  Any improvements will be in parallel energy storage (hybrid, kinetic, etc).

Franz

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RE: btu's per hp

Fuel economy comes from optimised engine design (pretty well much already there), reduced weight and reduced drag.

If you want 100 mpg, buy a moped. If you want 50 mpg, buy a Japanese micro car like a very small Dihatsu or Suzuki

Regards

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: btu's per hp

I worked on a car that got a genuine 80 mpg on highway, although to be honest it would not have passed modern crash regs or emissions.

Inside it was about as roomy as a Focus.

It was very light, had a high efficiency 3 cylinder, manual trans, and great aero.

Performance was pretty good due to the light weight and aero.

http://www.austin-rover.co.uk/index.htm?researchecvf.htm



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: btu's per hp

Let me use metric units initially as it's easier.

There is a force resisting motion due to friction and air resistance, which is so and so many Newtons. Multiplying top and bottom by metres, the resistive force is so many N*m/m and N*m is an energy unit called Joules. So the resistive force can be measured in J/m or kJ/km.

What that means is the resistive force is just telling us the energy required to go a distance, and taking its reciprocal, the resistive force tells us how many km/kJ the vehicle is capable of.

In imperial units that is saying the (reciprocal of) the resistive force is just a measure of how many miles/BTU you can get.

So to get an MPG figure, now isn't difficult

Miles per gallon = miles per BTU * BTUs per gallon.

As others have said, the BTUs per gallon require some assumption of engine efficieny, eg BTUs per gallon for the vehicle might be 30% of the figure you gave for BTUs in the fuel.

I'm not going to do any calculations for force resisting motion, as what one person finds an acceptable vehicle might be considered a joke to somebody else. However its easy to estimate from frontal area, coefficient of drag, etc.

Volkswagen created a street legal prototype (the so called cigar car) which consumed 1 litre per 100 km, which is 235 MPG US. 100 MPG is achievable by combining
(1) an efficient engine
(2) a low coefficient of drag
(3) a low frontal area
(4) driving well

RE: btu's per hp



I came across a calculation I have done some time ago, assuming a more efficient engine put in a Loremo and travelling at constant speed.

For all I know, it could be full of mistakes, but something in it might be useful to somebody.

CODE

Engine
0.35 lbs of fuel per horsepower hour
equals 0.21 kg per kilowatt hour
which gives 4.69870971 kWh / kg of fuel used.

Rolling resistance
Mass               450 kilograms
Add Driver and multipy by gravity
Weight             5297.4 Newtons
Use Coefficient of rolling resistance just over 1%
Roll Force         55.6227 Newtons

Air resistance
Wind resistance  (1/2) * airdensity * velocity * velocity * frontalarea * coefficientofdrag
 eg Loremo       (1/2) *    1.2     *   27     *   27     * 1.1           * 0.20
Air force          94.9662307 Newtons

Add air resistance and rolling resistance together

Air force          94.9662307 Newtons
Roll force         55.6227 Newtons
Total force        150.588931 Newtons
                 = 0.0418302585 kWh / km
       which gives 23.9061396 km per kWh

Finally, let's assume a compact fuel, eg diesel, rather than a less dense fuel like petrol.

Fuel Density    0.86 kg / litre

Fuel economy

Now we just need to multiply things together:
How good the car is at getting miles from energy
how good the engine is at getting energy from a mass of fuel
and how dense the fuel is.

                23.9061396 km per kilowatt hour
              * 4.69870971 kWh / kg
              * 0.86 kg / litre
Fuel economy  = 96.6020889 km / litre
             ie 272.272246 UK miles per gallon

RE: btu's per hp

That's an incredibly efficient engine.

Also Loremo won't achieve that Cd in practice. A looks low as well - draw a box 3.3 feet square and sit two people side by side in it.

Crr is a tad optimistic, for grooved tires.

And your final drive would appear to be at least 15 % less inefficient than any I've seen.


But yes, that's the way to do it.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: btu's per hp

An excellent link to BL Greg.

Pat, I think that references to 50mpg (Imperial gallons?) only being achievable in 'micro cars' aren't all that fair.
The latest crop of diesel vehicles from Peugeot and Ford of Europe are proving that (shared engine technologies).
A c-class vehicle will achive 50mpg, no problem and CD class are approachng these levels.

As for petrol engine technology development, what about the introduction of direct injection and the possibility of increasing the performance of pistons and combustion chambers by ceramic coatings?

Bill

RE: btu's per hp

I am continually reminded that the trick is not to get the guys who are doing 40 mpg, to do 60 mpg, but the neat trick would be to get the guys who are doing 10, to do 20.

And that is, to be honest, easy.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: btu's per hp

Sorry Bill

I forgot about the recent developments of light weight high speed diesels in Europe. We don't see many of them here.

Last time I was in Europe (about 10 years ago) I had a Reno 2 litre diesel. It was a quite slow of the mark, a bit noisy, but performed OK on the autobahn. It seemed to use as much fuel of a more expensive fuel as something like a Suzuki Swift of the era.

I guess things have changed.

Regards

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: btu's per hp

The odd thing is that fuel tank sizes seem to be fairly standard across all engine types.  This means that a modern small diesel vehicle has an awesome range between refuels.  

I often think that the best way to market diesel vehicles in the USA would be to focus on this attribute.  If the weather is nice, fill your car up.  If it's really cold, wait until a warm day.

RE: btu's per hp

A bit off-topic now, but, the big change in diesel vehicle acceptability has really come since the Fiat/Bosch introcution of small-engine common-rail diesel injection.

Calibrators are now able, using electronic control of turbo and fuel injection & timing, to dial-in fat torque curve, giving the driver a big-engine feel. These torques are also enabling quite high gearing for cruising. A 30mph/1000rpm top gear is not uncommon; accel is still capable due to the torques.
Check this, the writer notes a top speed of 124mph and 47mpg imperial:
http://uk.cars.yahoo.com/car-reviews/car-and-driving/ford-mondeo-tdci-diesel-euro-iv-range-1003354.html

Bill

RE: btu's per hp



Hi Greg

I used the manufacturers quoted figures for the mass, area and drag for the Loremo, vieable at http://www.loremo.com/daten_en.php. If you cannot get two people side by side in that area, try putting them one behind the other like in a Jetcar (pictured above), and the area might still be achievable.

Point taken that there are no transmission losses in the calculation.

I used engine figures from a press article by John Mortimer.
A google search on
"lb/hp-hr" "city car" mortimer
will throw up a link for verification, but I think the article itself is pay-to-view.

The coefficient of rolling resistance was from a thread on eng-tips - if I remember rightly. I tried to take the lowest street legal figure achievable, so the figure is intended to be low: if the aim is best milage one has to push the limits of area, drag, mass, etc.

If I redo a similar calculation sometime I'll put some transmission losses in: gearbox and final drive. I guess I should find a reference for the rolling restiance or change the figures too, as you're given a hard time on eng-tips if you cannot support what you are saying, l.o.l!

RE: btu's per hp

(OP)
Thanks again guys. I've been reading alot on vaporizing gas for fuel mileage and in theory this sounds good. Also there are many patents vaporizing gas suggesting this works. Knowing how inefficent a carburator is and how much fuel is wasted out the exhaust I thought there might be something to it.

   On the other hand I knew propane had less btu's, but it is vaporized before it reaches the engine and these people sure aren't getting great milage. Looks like I'll be building that Joe cell after all, just kidding.

RE: btu's per hp

Prius tires Crr is .011. Other car tires up to 0.015

Prius engine efficiency average 33%, max 37%. You should be able to beat that with a diesel.

yes, I know Loremo are making some amazing claims. I like the idea, and even with more realistic numbers in it still makes sense. The Cd is achievable on a prototype, but will need a fair bit of stuff that is not realistic in a light production machine.

You have reminded me that Cd and A is a bit of a misnomer. In cars the surface area is really what matters, frontal area is not the most important parameter on a well deisgned car. That is, I can get lower overall aero with a larger A sometimes.



 

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: btu's per hp

All you Deisel fans, remember, diesel has 15% more BTU's gallon.  For fuel vaporizers, switch to propane, its already vapor if carburated into an engine. and it has 20% less energy than gasoline per gallon.

RE: btu's per hp

We're talking about thermodynamic efficiency, not gallons per bhp hour.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: btu's per hp

Well, Greglocock, you are talking thermo, but most people like WGJ are on MPG.  The fad is switching to diesel, but it isn't a one for one competition, its emotional and a mines better discussion.  The biggest thing we can all do to lower energy used is DROP the weight.

As a side note, the US EPA has set a new standard for running the MPG tests that are posted on vehicles.  The new test more closely mimics how people drive.  The results are most cars will have a 8% reduction in MPG for city and 12% for highway.  The high effiency vehicles ove 30 mpg will be hit 15% / 20%.  The hybreds will get wacked 20%/30%.  Again, hybreds are just a fad, you can't add 500 pounds of motors and batteries and get that much farther ahead.

RE: btu's per hp

The OP asked a Thermodynamic efficiency question with a hint that it related to fuel efficiency of his car.

He considered weight only, and considered maximum power. This indicates he knows very little about the subject, or meant to be very specific in looking at thermodynamics.

He did quote a BTU value for the fuel, so that should exclude all fuels not of that value.

Regards

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: btu's per hp

Just for the record Henry "Smokey" Yunick (yes I borrowed my screen name from him) got the nick name from a track announcer reffering to a motorcycle he had raced that blew a lot of smoke from the exhaust. Regarding the hot vapor engine I saw two working examples of this method both were sawed off from a buick v-6 3.8liter. A 2cylinder version is in a vw rabbit that is in the storage area behind the pet store his daughter operates in Holly Hill FL. The other one is a 3cylinder version that he had in a Ford Fiesta for many years. That engine is in a storage warehouse for the Smithsonian institute. Smokey's grandaughter was still driving it around (original engine was put back in) as of may of last year. I had the privledge to speak at legnth with  2 gentleman who worked along with Smokey on some of his projects. One was an engineer who's career started at GM on the original rochester mechanical fuel injection system, worked for holley carburetor( major contributor to the deign and developement of the holley 4160) and recently retired from an R+D position at Crane cams. The other was a more hands on employee. Both of them along with several friends and family who drove vehicles with one of these engines in place report gasoline fuel milage figures in the 60 mpg range. The 3 cylinder version was capable of 200 hp. The intelectual property rights to the proccess were licensed to the Delorean Motor Co. and after the demise of that company Crane cams along with Smokey formed a company named Motor Tech that was going to develope and market it in kit form for retrofit in the aftermarket. Most of this information is public and fairly easy to obtain. In answer to the original question from this post I do believe the technology exists today for a gasoline fueled 3,500 lb vehicle with a drag coefficient of .40 to achieve 100mpg. I believe the biggest obstacle is that fuel prices are still low enough that it is not cost affective to offset the higher cost needed to manufacture such a vehicle.----Phil

RE: btu's per hp

SMOKEY, your car would have to use less than 40 HP and the engine be better than 50% efficient, so its max speed would be 40 mph, it would not go up a hill to save its life.  As for fuel price dictating car design, fuel in europe is $5.00/gallon and they are not at the level you predict, close, but not quite there.  
Its not the fuel price, its, not anything we have control over.  The US public wants a car that is bigger than their neighbors so if they collide, the neighbor will die and not him.  Second, we want cars that will pull a 12,000 pound trailer (just in case we need to tow away or nieghbors car from a crash site), go 0 to 60 in under 6 seconds (just in case we have to evade our neighbors car), have every electric gadget known to man (because our neighbor does, at a cost of fuel), AC to chill us to the bone (never see the neighbors window down, heck the AC drops my milage by 10% when I run it).  Its not the fuel, its peoples perception of what they think they need.

RE: btu's per hp

I think a 3500 lbs car could get 100 mpg if you could regenerate 80%+ of the braking energy at 80%+ total efficiency, and you use multiple 4 stroke linear engines and are city driving in a city without many hills.
The reason for many linear engines is to have a longer power stroke than intake, then only operate the number required to propel the vehicle. No crankshaft engine will have the same efficiency at different loads and speeds. The power to the wheel varies from little to a lot depending on terrain, speed and if you are accelerating.

RE: btu's per hp

Vapourising the fuel might get greater combustion efficiency, preventing unburned fuel going out the exhaust.

That would help if that were a major source of engine inefficiency, however it is not. Virtually all the fuel is burned and turned into heat well before the end of the power stroke. This means that any improvement can only be small as there is not much room for improvement. Like I said earlier, in a modern petrol engine, about 1/3 goes to the cooling system. Vapourising the fuel won't change that very much. About 1/3 goes out the exhaust. Vapourising fuel won't change that at all.

Vapourising fuel might give a slightly faster burn rate. This will require less timing advance to avoid detonation. This later ignition will give less time at higher cylinder pressures, so a little less will go to the cooling system, also less power will be consumed pushing against cylinder pressure on the late compression stroke and all available heat will be generated earlier in the power stroke so more work can be extracted, but at this stage it will also put more heat into the cooling system. There might be one or two percent in it. A long way short of 100 miles per US gallon.

Smokey might have obtained very high MPG figures, but it was not down to the fuel heating. He had many other significant mods, not the least of which was half an engine. I strongly suspect he used smoke and mirrors as a diversion from the real causes. While everyone focused on the fuel heater, no one noticed other features that do work.

State of the art very small engine, light weight, good aero, hard small tyres, constant low speed, simple light weight transmission are the secrets to low fuel consumption

Regards

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: btu's per hp

The heat of vaporization for hydrocarbons is about 130 BTU/lb, The heat of combustion with the total recovery of heat back to 60 F, including the condensing of the water vapor formed is 21,000 BTU/lb, so vaporizing the fuel first will incease effiency by 130/21000 by .6%, can't argue thermochemistry.  The recondensing of the water in the exhaust is about 2000 BTU/lb of fuel burned, so the water vapor alone has 9% of the thermal energy available. The exnaust it's self is where the majority of the energy goes.  At a 700 F exhaust temperature, there is another 30% of the efficency lost.

I have a home heater that is 92% effcient, the exhaust of the heater leaves the house just 30 degrees warmer than the air intake to the burner, it condeses the water by preheating the air.  So if we want cars that can achieve this kind of efficency, lets go back to the steam car, or put a combined cycle system where the exhaust gases are make steam that drives turbines to get energy.......

RE: btu's per hp

Which is perfectly feasible, technically, it just isn't worth doing financially. (yet)

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: btu's per hp

GregLocock, agreed.  Can anyone agree that a 80% efficient internal combustion engine isn't possible unless we get "waste heat recovery" and that this type of recovery isn't practable unless we find some way to use it in a vehicle?

RE: btu's per hp

dcasto I agree with you that waste heat recovery is the path to achieve that objective. I think turbo compounding will get about 60% of what's available from the exhaust but it will only be optimum at a specific rpm and load. I also think that steam driving a second turbine using heat from the cooling system and whatever is left over in the exhaust is the best method to do that. Packaging is somewhat cumbersome but doable. I have spent most of my spare time in the last 4 years and mega$$$ retro fitting an existing vehicle with the methods decribed. It works but I won't live long enough to offset the cost in fuel savings. Throw  the economy of mass production into the mix and your probably looking at a ten year break even payback. I am not much of a profit but I believe that fuel prices will rise enough in about 5 years to make it economically viable.-----------Phil

RE: btu's per hp

A 10 year payback in an environment with 10% interest means the capital is never reduced let alone paid back.

Regards

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: btu's per hp

How about a thermal generator to make electricity out of the exhaust, that might get 5% or so.  Switch from compression AC to thermal AC, like a propane refrigerator.

RE: btu's per hp

Yup. Peltier devices after the cat have been demonstrated.

The trouble is that Carnot tells you what the max efficiency of the entire system is going to be, so until we can figure out how to extract all of the enrgy at high temperature, we are never going to see much better than 60%.

Of course, the reduction in fuel consumption is much greater in going from 20% to 40%, than 40% to 60%.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: btu's per hp

Years ago I believed in the 200 mpg carburetor.  Then I got into propane.  I realized that burning propane was accomplishing the same goal; to burn fully vaporized gas.  Propane has 30% less btus than gasoline.  But I found that I didn't get any outstanding mileage with lp, in fact it was worse than with gasoline.  On a modern engine with feedback electronics, lp power will get 20% less mileage than gasoline.  That tells me that there is only about 10% room for improvement for gasoline mileage by vaporizing the fuel, not 500 or 1000%.  Last year Bruce Crower of Crower Cam fame came up with a 6 stroke engine that I think is revolutionary.  Instead of opening the exhaust valve on the 4th stroke, it compresses the exhaust gas.  Around TDC, an injector injects water.  The water hits the hot gases and vaporizes, providing a second power stroke.  It exhausts on the 6th stroke.  The engine needs no cooling system, and he says it provides around a 30% efficiency gain.  He is able to recover almost all energy from the exhaust.  A downside is that you now have to carry water as well as fuel as a consumable, and the water has to be distilled.  Keeping moisture out of the oil would be a challenge on a cool running engine.  Crower developed this on a one cyl diesel engine that he fitted with an ignition system and carburetor, then used the injection system to do the water.  Of course he had to completely change the cam setup to run at 1/3 speed instead of 1/2.  

RE: btu's per hp

I'm not much of a thermodynamicist, but the Crower 6 stroke cycle p-V diagram doesn't look like a winner to me.  Anyone want to comment on the T-s diagram?

RE: btu's per hp

Here is actual data with effiency from a spark ignition engine

Caterpillar G16CM34
     6100 bkW @720 RPM
     7671 BTU/bkW-Hr
     7909 BTU/ekW-Hr*
     44% Efficiency
     0.5 Gm/BHP-Hr NOx
power output       5.9    MWe
 cylinders &      arrangement    16Vee    
 cylinder output 380    kW/cyl
 bore       340        mm
 stroke       420        mm
 speed       720/750    rpm
 fuel       Natural Gas            Methane > 70    
 Fuel Cons        7909        BTU/ekW

RE: btu's per hp

A rough estimation for brake specific horspower per imperial gallon is 45hp/gallon/hour

RE: btu's per hp

my friend, professional chip tuner was experimenting with 3 cyl.diesel vw lupo last year.He was driving at "ecology rallye" wich happens every year in Lithuania ant took second place.His lupo at 105 km/hour eats average 2.5 liter diesel no highway - country asfalt road.Car with all guts - full interior and ordinary tire pressures,driver alone.

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