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water injection to gas engines
7

water injection to gas engines

water injection to gas engines

(OP)
Some time ago I was looking for options to inject water to a gasoline engine to improve power and milage and read several of the opinions. I got discouraged because the practicality of it was not there to compensate for the trouble, but I was surprised nobody could explain why the water injected into the combustion air would improve eficiency.

Opinions ranged from no benefit to confirmation that on wet days the engine seems to run better. The point is why?

In my opinion the explanation is that of adiahbatic cooling, that is cooling without heat transfer, the better known exaple of this is to cool air through humidification in hot dry climates.

If you inject water to combustion air the air will cool off thus reducing it volume and therefore increasing the oxhigen concentration, much the same way an afterccoler does.

Does it make sense?

Pisto

RE: water injection to gas engines

" nobody could explain why the water injected into the combustion air would improve eficiency"

You sure about that?

SAE paper 1999-01-0568   Water injection effects in a single-cylinder CFR engine
     
    Author(s): Lanzafame, R.,

Cheers

Greg Locock

RE: water injection to gas engines

(OP)
To Greg Locock:

Greg, whay I am sure about is that if to dry hot air you add water the air cools significantly and following the law of gases, if you cool a gas it reduces its volume and if the oxygen content remains the same that means you actually put more oxygen per cubic feet of air to the engine.

I would say then that if you leave in a hot dry area (Las Vegas for instance) your engine would improve eficiency more by injecting water than if you live in Portland where the temperature drop would not be significant, so it depends on the intake air conditions also.

PISTO

RE: water injection to gas engines

PISTO

I think you are right about the latent heat of vaporisation af the water and volume and climate, however a running engine is a dynamic situation and it gets a bit more complex. ie if you reduce the volume after the air is in the cylinder, and the valves are closed, no more oxygen can enter the closed system. Iwould suspect that a significant amount of the water evaporates on the compression stroke and dureing combustion.

The main benifit of this is to prevent detonation by effectivly reducing peak cylinder pressures before and just after ignition.

This in itself will probably reduce power if no detonation would have occured without the water. It only improves power by allowing a higher compression ratio, or more boost in a forced induction engine.

I think this was covered in great detail in several previous threads

Regards
pat

RE: water injection to gas engines

(OP)
Pat:

I think the clue is not what happens inside the cylinder but on how much oxygen enters the system and I think more oxygen enters as a result of the reduced volume by cooling the air before entering the chamber. What happens afterwards, inside the cylinder is another system.

I think, for practiacl reasons, what counts is how much benefit you get under normal conditions and how much does it cost in money and troubles to have a system that adds moisture to the air, as for me I decided it is not worthwhile, even though I live in a dry area for eight months a year.

PISTO

RE: water injection to gas engines

Several different combustion variables are affected by water injection.

1st. charge cooling.

2nd. slowing of flame front speed, improving combustion completion.

3rd. additive effect expansion, when water changes state from a liquid to a gas in the heat of combustion.  the ratio of expansion of water from a liquid to a gas(steam) is about 600 to 1.

While any one variable may not be significant; the sum of the three do have a positive impact on engine performance.

REDMANE  

RE: water injection to gas engines

(OP)
REDMANE

Good point, I overlooked the expansion factor of the water in the combustion.

But still the issue is if it would be practical to install a water inyection system on passenger cars for intance or diesel truck engines. The volume of water would need to be controled in proportion to the volume of air either electronically or vacum which is proportional to the air volume in a way.

If somebody knows of a system that is simple, simple to install and inexpensive let me know.

PISTO

RE: water injection to gas engines

Spearco make an electronic and vacuume controlled unit

Regards
pat

RE: water injection to gas engines

Read previous threads for details

Regards
pat

RE: water injection to gas engines

If water evaporates in the manifold, it cools the aie, but also displaces a substantial part of it, so yuo end up with a denser charge containing a lot of water vapour and less oxygen.

To get the benifit of high expansion ratio, you need to turn the water to gas IN THE COMBUSTION CHAMBER.

If you ever had a chance to look at an engine running with a transparent manifold, I am told by those who have, you will be amazed at how much liquid fuel is thrashing around in there. Greg Locock has done this, and is my source of that information.

Water has a much slower evaporation rate than petrol. Just leave a cup full of each in a safe open area and see the difference

You will find some research papers on this site http://naca.larc.nasa.gov/
It's part of NASA's site and is an archive of research into aircraft technology. Water injection was a topic of interest before and dureing WW11

Regards
pat

RE: water injection to gas engines

Correct me if I am wrong - but won't the water only evaporate to 100% RH and then the vapor and liquid water will stay in equilibrium?  And as the charge cools the ability to maintain water in vapor becomes increasingly difficult resulting in much of it condensing back into liquid.

Experience and many papers have illustrated that the density of oxygen is not reduced by the injection of the levels of water normally used which are almost always less than 1.5% water to air and frequently less than 1%.

Additionally injection in the combustion chamber does not provide the cooling of the intake valves that provides improved VE.

You will lose the expansion ratio benefit to the extent of water that does vaporizes but only to 100% RH.  The liquid and present water in the charge will remain effective.

Also the expansion of the small amounts of water we are talking about are not as significant as the role water plays in the completion of the C0 -> CO2 oxidation which is where substantial amounts of energy is released and which can only effectively be achieved by the presence of water - the more water there is in the mixture the faster this powerful part of the combustion process will occur.  BMEP is increased by water injection primarily increasing the rate of this otherwise slow step in combustion.

RE: water injection to gas engines

That's pretty well my point

Earlier in the thread, it was stated that the power gains from water injection were due to the cooling effect increasing the VE. I stated that most of the improvement came what happened inside the combustion chamber.

This wasn't accepted, so I let it go.

This deal has been covered in great detail in earlier threads.

I can't see a lot of point in repeating it all again.

The real quantifiable benifit of water injection is that it stops detonation in engines where the fuel is inadequate for their compression ratio

The real fringe benifit is that it decokes the engine.

The real dissadvantage is that you might destroy an engine if the water injection system fails

You can also destroy an engine by hydraulic lock if the water ever syphons back into the inlet when the car is parked on a steep slope.

I have never seen any evidence to suggest that a well tuned car leaves a lot of CO after the power stroke is complete, unless the car is deliberately rich to cool the charge and help avoid detonation. Water is certainly the better solution to avoiding detonation, when compared to extremely rich mixture.

You are absolutely correct re the relative humidity thing and temperatures. Little water will evaporate until the temperature is raised substantially, like dureing the later part of the compression stroke, and even more so at the point in the power stroke where the flame really gets going.

Regards
pat

RE: water injection to gas engines

Remain open to possibilities.

The Graneau-Graneau exploding water experiments show a sudden reduction in H2O-H2O cohesion. No steam is generated.

How many labs are currently studying this phenomena? I know of at least four.

Could an internal combustion engine act as a catalyst for the process?

RE: water injection to gas engines

Very interesting thread for me.  Short anecdote.  I was present for a dyno tuning session on a 1.3L 2V race engine.  CR was over 13:1.  Weber carbs on an IR setup.  We had made quite a few pulls when the engine builder running the dyno suddenly shut it down.  We asked why and his response was that the engine had suddenly started "making too much power".

We pulled plugs and looked at crowns.  #2 cyl was far too clean.  Pressurised the coolant and found a trickle in the #2 intake runner.  I've been interested in water injection ever since.

RE: water injection to gas engines

Correct me if I'm wrong, but I believe that general combustion theory states that the power an engine can produce is proportional to mass flow.  Increasing the density of your combustion mixture by adding water should do this.

One may also want to check the expansion rates of H2O vapor vs. air.

Previously discussed theories should also prove true.


Also, I live in a particularily dry climate.  Driving in the rain shows marked improvements in both milage (up to 20%) and power.

RE: water injection to gas engines

How can the density in the cylinder change due to flow, after the inlet valve closes.

The mass flow only normally applies to air, and the oxygen it contains. It may also apply to other oxidising agents such as nitrous oxide, but that is a whole different set of circumstances.

If the water evaporates in the manifold, it cools the air, but also displaces it with water vapour, having a net reduction in air density, consequently also reducing the mass of oxygen in the charge in the manifold.

Actually, very little water evaporates in the inlet tract, or in the cylinder before the valve closes.

Re your fuel economy gains, you probably slow down a little in the rain, even if it feels faster because the car is slideing about and spinning wheels.

The auto company engineers do know about water injection. It was used by engineers in aircraft dureing WW11, and if I remember corectly, there are research papers dating back to WW1. I really can't be bothered repeating the research again, so you will need to do it yourself if you really want to know.

I have already given links to sources of research papers, as has Greglocock and Turboice, if anyone wants to read real data.

This subject has been covered extensively in previous threads.

I for one will not further waste my time trying to explain simple facts again and again to those who do not look up the previous posts or threads, or links.

Regards
pat

RE: water injection to gas engines

Pat wrote: If the water evaporates in the manifold, it cools the air, but also displaces it with water vapour, having a net reduction in air density...

Well, I always wondered if that were true so I did the math.  It turns out that the net effect is an increase in O2 density, albeit quite small for NA charge temperatures (and, of course, taking into account various assumptions).  Here's a link to my results:

http://not2fast.wryday.com/thermo/water_...

RE: water injection to gas engines

3
Another consideration:

It requires less work to compress cool air than hot air.

I did the calculations comparing the amount of work it takes to do a 10:1 compression on air at 70 deg F and 110 deg F.

At 70 deg F: 88.7 BTU
At 110 deg F: 94.9 BTU

For an engine running 20 pounds of air a minute (roughly the amount of air a 5.9 liter "Ram Diesel" with a turbocharged engine runs at 1800 rpm), the horsepower the engine uses compressing air during the compression stroke is as follows:

At 70 deg F: 88.7 hp
At 110 deg F: 94.9 hp

Using some engine simulation software I compared the engine brake cylinder efficiency at the two temperatures. At 70 deg F the efficiency was 43.27%; at 110 deg F it was 42.65%. For a diesel engine flowing at 20 lbs/min this would work out to about 2.5 hp.

It appears to me that another effect of water injection may be to decrease the charge temperature and therefore decrease the amount of work the engine has to do during the compression stroke.

RE: water injection to gas engines

SBBlue - that is an excellent insight - I am going to need to add that to my write up on WI.

RE: water injection to gas engines

(OP)
ErickFahlgreen.- Very good work, I will study the charts.

SBBlue.- That is a good point and one more reason to consider water as an option to increase power and efficiency.

Patprimer.- I think the clue is that what you are modifying is the relative humidity of the air while entering the manifold that produces an adhiabatic cooling (temperature reduction without heat transfer) same as those new room humidifiers, with the subsecuent reduction in volume and increase in O2 concentration. There is no point in adding so much water that water vapor (in case temaperature makes it boil)will displace O2.

I think the point is to relate the benefit at diferent relative humidity of the intake air, then evaluate other forms of using water injection DIRECTLY into the chamber to take advantage of the expansion factor.

So one thing is to air moisture to the air before entering the chamber to increase O2 and another system is water expansion inside the chamber. If both are used then add up the benefits.

Looks to me this is something worthwhile taking by someone that has a laboratory and could run lots of tests under diferent conditions to evaluate the practical and economic impact before a serius application is considered.

PISTO

RE: water injection to gas engines

Re Patprimmers comment about slowing down in the rain casusing apparent fuel consumption improvement and BHP gains has a hole in it - many drivers have said that cars pull noticeably better on damp days i.e. those where the there is high humidity but no standing water on the road.  Why would you drive slower because there are low lying clouds, and why would 'the car is slideing about and spinning wheels'under these conditions?

Sorry, but damp days REALLY DO improve performance.

I managed to mimic this with a latex microbore hose fed into the carb intake.  The other end of the hose was sitting in a jar of water.  The engine vacuum drew water through the hose in proportion to the rpm it was turning.
Result?  A small but noticeable increase in response.

Surely someone with more time and the appropriate measuring equipment could rig up something to reproduce that in a professional capacity.

RE: water injection to gas engines

(OP)
Andybee:

I agree with you about better performance on wet days, I happened to notice that a lot when I had a small VESPA scooter with a 150cc two stroke engine.

Of course someone living in Vancouver may not notice a diference year round, while someone in Las Vegas might.

Just one coment about the way you injected water. If you injected water directly into the carb you probably benefited only from the expansion of water in the combustion chamber, but I doubt you got the effect of cooling the air before entering the chamber with its corresponding volume reduction increase of O2 concentration, I think, for that you would need a device that produces a light mist to rise humidity and probably some time before it enters the chamber.

Yes, I wish someone with the means could go into this and come up with a simple device that controls this.

PISTO

RE: water injection to gas engines

I have an Autogas system on my Rover V8 (3500cc) which runs twin SU carbs.  The gas is fed from an aspirator / vaporiser unit (several names for it) as the vacuum demands it.  There is a diaphragm system acting here, as the intake vacuum increases, more gas is delivered. So couldn't the same method be used to deliver a mist?

Patprimmer (above) said Spearco make an electronic and vacuume controlled unit  - is this the solution?

Yes, my latex pipe was primitive, but it proved the point, and improved the performance.

RE: water injection to gas engines

I think the Aquamist 2s would do what you are suggesting.  It would take a bit of of a different approach to do it with an N/A motor since one of the matrix loads is MAP and meant for forced induction.  If you could provide another signal indicating load such as vacuum or throttle position the 2s will meter the amount of atomized water you desire at any location that you place the jet based on RPM and your chosen load reference.

Ed.

RE: water injection to gas engines

I don't think that adding water to a stock engine is a good idea. The high temperature steam will probably cause more corrosion problems in the cylinders and the exhaust system than you will save on gas. If you have ceramic cylinder and stainless steel exhaust, maybe

RE: water injection to gas engines

Glueontop... are you aware of the by products of combustion?

RE: water injection to gas engines

Andybee, your simple system is not at all primitive, but very practical.  Small engine manufacturers are still using vacuum/syphon venturi carburators and although simple, they do work well with little trouble.  I had been thinking of trying to incorporate a sonic humidifier, this may be easier.

I'm not so sure the injection of water causing a COOLING effect to the charge has much merit in the investigation of why water injection works.  

If COOLING the charge results in an increase in power/efficiency, then operating an engine in severe cold should be optimum.  Anyone who lives in a cold climate can verify that as false.  We also know colder air is drier.

Also, it would make false the fact humidity plays a very real effect on efficiency and power.  Humidity provides NO COOLING effect at the intake of an engine.

However, we do know intercoolers do work.

I also looked back into a text I have and elementary Otto cycle theory does state mass flow is important in regards to power and efficiency. (think... if a lean A/F mixture provides optimum power and efficiency-->burns hotter, why does adding more fuel also work?-->burns cooler)

The conclusion I draw from these few statements (without attempting the math behind them - I'd like to see it verified for disproved)

Water injection into the intake of an engine should do two things.  It should provide evaporative cooling (same effect as intercooling) and it should raise the water vapor content of the charge (same effect as humid air).

That's my 2 bits.

RE: water injection to gas engines

Injection of water definitely will cool the charge if the relative humidity of the charge is less than 100% relative humidity.  The evaporation of liquid water up to 100% relative humidity will reduce the charge temperature.  The ability of the water to do that is very dependent on the charger temperature and the induction length after the injection.  Clearly on most NA systems the induction is short and there may not be enough time to reach 100% RH before the valve.  The cooling effect to the extent it exists is much more noticeable in dry climates than humid climates.  See this link: http://not2fast.wryday.com/thermo/water_injection/opt_m...

Humidity provides no cooling effect because water vapor has much less latent heat than liquid water.

Cold air is denser and will be more efficient and powerful.  The difficulty in extreme cold climates is getting the motor to operating temperature not that the induction charge is too cold.

Efficiency AFR and Power AFR are on opposite sides of stoich.  Otto motors max efficiency is slightly leaner than stoich and max power is slightly richer than stoich - http://www.turboice.net/?documents/turbowhitepaper/tuni...

Ed.
www.turboice.net

RE: water injection to gas engines

OK
I will comment further as a few guys who have some understanding, and thinking capacity have contributed.

Thank you Canadatech, SBBlue, EricFahlgren, Greg Locock, Redmane, and turboice

Eric, thanks, I never actually did the math. Bottom line is, that's not where the real improvement comes from, it comes from supression of detonation, and the expansion characteristics of water to water vapour IN THE COMBUSTION CHAMBER.

792003, As I understand it, WW11 aircraft had a throttle stop with seals. The pilot was allowed to push the throttle past the stop and break the seals for EMERGENCY WAR POWER. It is extra boost that gave the supercharged engines in the WW11 planes their extra power, and the water injection was used to avoid detonation when useing this extra boost. Once thre throttle stop seals were broken, the engine had to be dissaembled, checked for damage and rebuilt. It is a good way to remove carbon deposites in anything from a Mack truck to a Vespa.

PISTO, Adhiabatic cooling is not all that new, it was used prehistory by man, as they sat by the river, pond or whatever because it was cooler, or wet themselves down to cool off. It was first deliberate controlled by the ancient Romans when the built fountains in their courtyards over 2000 years ago. There is a point to adding more than enough water than required to reach 100% RH in the manifold, as RH changes with temp and pressure, therefore more water evaporates as the temp increases on the compression stroke and dureing combustion. Normally the easiest place to add all the water is near the carby or inlet to the plenum. A lot of work has already been done in some really serious laboratories like Rolls Royce, Packhard and Allison aero engine departments, the SAE, and NACA (who just happen to be the precursor to NASA, but what would they know)

SBBlue, A very interesting insight, but you only looked at halfthe reaction. As the water evaporates, it absorbs latent of vaporisation and thus cools the charge, thereby reducing it's volume, and concequently it's pressure, but it also adds water vapour to the charge, increasing its volume and pressure, I have not done the sums for the net result. Maybe Eric still has his calculator out.

Andybee, Yes the Spearco system does work, so long as you use some alcohol in the water to kill algee, and preferably filter the water between the pump and the jets, to remove potential blockages.

Andybee, I don't care what some drivers say, DYNO'S say engines make more power on cold days, but less power on humid days. This is because cold air is more dense, but a molecule of water vapour will displace oxygen in the air. Dyno's provide objective data, drivers only provide subjective data.

I have used this "theory" to tune my race car. It has a supercharged 350 Chev, with constant flow mechanical injection and runs alcohol. It has 11:1 compression and 30 pounds boost. As this type of injection has no means to correct itself for air density changes, I need to tune it to the weather by changing jets before every run. I calculate air density from pressure and temperature figures, and the higher the density, the more fuel I give the motor, BUT, THE HIGHER THE HUMIDITY, THE LESS FUEL I GIVE THE MOTOR.

We recently ran the 1/4 mile in 8.33 sec at 161 mph in a 2600 pound street registered car, and won our class at a national meet. I have never had a problem caused by incorrect mixture when useing this methodology.

READ THE PREVIOUS THREADS AND THE LINKED SITES AND PAPERS
         

Regards
pat

RE: water injection to gas engines

CANADATECH...

I am well aware of the combustion process. But the reaction is not instantaneous. in fact, at the speed most recent engine revs, the water will not have the time to vaporise and react before it is pushed out of the cylinder. So there will be steam for a significant amount of time in the cylinder.

Some petroleum companies are starting to sell water/diesel emulsion to solve the problem. the water is emulsified with the fuel and not injected as two components. and this is for slow reving large diesel engine.

RE: water injection to gas engines

The point he was making is that steam is a substantial byproduct of carbon combustion - the steam is in the exhaust anyway.  The amount contributed by water injection is small by comparison to the already existing steam byproducts.  The idea that injecting 2% and less water into the induction charge is going to contribute to corrosion is flawed at best - motors in high humidity climates would corrode just as fast in that case.

Glassman's work shows that water is very active in the combustion process - the reactions it plays a part in are plenty fast enough.  Evaporation and combustion are not instantaneous but under compression it is much faster than you are giving it consideration for.

RE: water injection to gas engines

the thing is that the humidity present in the air at the intake is already in the gaseous phase, so it doesn't have to vaporise.

the second point is that the gasoline that you take at the pump contains a certain amount of rust inhibitor additive that is based on the average climate where it will be used. So it already takes into account a certain amount of water present in the mixture.

I think that adding water to the intake mixture is a good idea, but not in a conventional engine. Keep in mind that most people want an engine that last for at least 200K Km, without any major problem.

finaly, a large portion of those who own a car live in a place where there is a risk of freezing. So good luck with your water tank in the trunk, and your first starting in the morning when the valves and the pistons are frozen! If you realy want to save on gas, buy a smaller car.

RE: water injection to gas engines

As for the testimonies, the obvious flaw with the "more power on rainy days" anectdote is they are missing the fact that most rainy days are also COLD days. That's where any power increase came from

RE: water injection to gas engines

If you add some ethyl alcohol to the water, it will substantially lower it's freezing point.

There is often free condensed water laying in the exhaust system of cars that are only used for short, low speed trips.

This water is a major byproduct of the combustion of hydrocarbons. The extra added by a water injection system, that is designed to only activate at low manifold pressures, will be insignificant, and will mostly only be added in circumstances where enough heat is being generated to clear out the water in the exhaust.

The ways to stop exhaust corrosion in cars with water retention problems are:-
  use the car harder and longer. This might not be acceptable to the owner.
  Drill a small hole at the lowest point of any puddles of water. This might generate a small but anoying noise, but the muffler will last a lot longer.
  Locate the muffler closer to the engine.
  Use stainless steel in problem areas.
  

Regards
pat

RE: water injection to gas engines

Methyl alcohol is a bit easier to obtain for water injection since it is a primary component of windshield antifreeze solutions and gas anti-freeze like the yellow bottles of heet.

Additionally at least one study has shown that methyl alcohol mixed with water provides more knock suppression than water alone.  Good mixture testing reference: http://naca.larc.nasa.gov/reports/1945/naca-report-812/

Also methyl alcohol is a fuel.

I use 50/50 mixtures year around.

Lastly some pumps and other components are negatively affected by ethyl but not methyl.

And you are dead on about the true source of exhaust rust (retention of liquid condensation rather than the passage of steam) and the solutions.

Ed.

RE: water injection to gas engines

Methyl and ethyl alcohols have VERY similar properties, as they both have the same functional groups, and basic structure. Methanol being the smaller molecule tends to react in the same way as ethanol, but a little more aggresivly

Over here (Australia) ethyl alcohol is easier to buy. We don't normaly encounter freezing conditions, so antifreeze is not always avaliable, other than glycol based coolant that is.

Ethanol is avaliable from supermarkets, garages, corner stores etc as Methylated Spirits, or in some countries I think it is called denatured alcohol.

Both work fine, both are fuels, both increase octane, but methanol does it a little more, both mix well with water, both can cause corrosion problems with aluminium fittings, but methanol is substantially more reactive in this regard. Ethanol requires a weaker A/F ratio than methanol, so it will nor enrich your mixture quite so much. Both burn very clean.

Also, ethanol is somewhat less toxic, in fact many people deliberately drink it regularly. It is actually more toxic than many realise.

It really comes down to whats easiest and cheapest to get.

I hope I havn't rambled on to much.

Regards
pat

RE: water injection to gas engines

Nope you are right that we (or at least I) need to appreciate the availability of alcohol types in other regions.

The pumps I use can take 50% methanol but no more than a few percent of enthanol or isopropyl.  Other pumps can take much more concentrations of alcohols.  The issue is the seal material and how it reacts to the particular alcohol.  While ethanol and methanol have many similarities just like heptane and octane have very different characteristics from a couple molecules so do ethanol and methanol.

And yes methanol is highly toxic if ingested - but is safe to handle in the manners being discussed here.  Ethanol is highly controlled in the States exactly because it can be ingested - toxins are freely available though. :)

RE: water injection to gas engines

If you surf the net you will find at least a hundred pages of people who claim they have built a thousand HP engine running on water, or the story of a guy who was killed by petroleum companies because he invented a water running engine. In fact water contains no energy and cannot be burned. This is a dream!

What is one of the first thing they do with crude oil at a rafinery? they remove water. What is one of the last thing they do with gas before it leaves the rafinery? They put corrosion inhibitor and anti-coalescer addithives. These steps cost hundreds of millions of dollar a year to the petroleum industry. If water in an engine was not an issue, they would keep there money.

There is two laws of thermodynamic that explain what appends in a combustion engine. The first is the ideal-gas law   PV=nrT. It says that in order to increase the pressure in a vessel, you have to increase the temperature. So at any point in time after the explosion, you want to have the highest temperature in the cylinder to get the maximum power. If you add water, a part of the explosion energy will be used to heat the water, this will reduce the temperature of the reaction and thus, the pressure in the cylinder.

The second law is the Otto cycle. It says that in order to increase the efficiency of an engine, you must increase the temperature difference between the time before and after the explosion and/or increase the compression ratio. Both are limited by the gas quality available. Water doesn't contribute in any way to the achievement of these goals.

These laws have been proven time after time for at least a hundred year. No one has ever prove them wrong, and no one ever will.

RE: water injection to gas engines

Andy330hp,
You must have missed my earlier post.  We were on a Stuska water brake dyno.  An aberration caused a unexpected increase in torue.  Same day, same air temp, same everything except we found a leak in an intake runner.  The builder was sharp enough to shut down and was not really surprised when we reported the leak to him.  Water temp was probably right around 195F.  Maybe 10% antifreeze with a little water pump lube added.

The caveats here are that we were dealing with an engine on the edge of detonation and that a 2% gain would have been big news.  Fuel was 114 octane gas and air temp was above 90F.  The leak only would have affected one cylinder, and yet the torque increase was noticed and reacted to by the builder.

Isn’t humidity one of the correction factors for normalizing dyno figures?

RE: water injection to gas engines

Glueontop discussed the ideal gas laws and Otto cycle thermodynamics, and concluded:

"These laws have been proven time after time for at least a hundred year. No one has ever prove them wrong, and no one ever will."

What you say is true. . . .but, as Paul Harvey would say, there's the "rest of the story" that needs to be told.

First, what you said about the ideal gas law and the Otto cycle could also be said of the open Brayton cycle, i.e., the Gas Turbine. Yet there is no question at all that water injection into the compressor of a gas turbine increases turbine efficiency. Here are some websites of companies that specialize in gas turbine "inlet fogging":

http://www.amco.com/power_generation.htm

http://www.air-process.com/inlet_fogging.htm

http://www.realfog.com/turbine/gtps-ifbc.html

Second, your comments about the ideal gas law and the Otto cycle only apply to single substance systems.

Consider the following;

Take one pound of air at an atmospheric pressure of 14.7 psi and a temperature of 1000 deg F. Mix this with one pound of steam at a pressure of 14.7 psi and a temperature of 212 deg F. What do you get?

Clearly heat will be transferred from the hot air to the steam, and the temperature of the steam will obviously be equal to the temperature of the hot air. If you work out the problem with the steam tables and ideal gas tables, you will discover that the resulting mixture has a temperature of about 490 deg F and a pressure of about 15.3 psi.

Note that the temperature of the hot gas dropped after we added the steam to it, yet the pressure of the mixture increased. Obviously, if we couldn't get any work from either the steam or the hot air prior to mixture because they were already at atmospheric pressure, and there wouldn't be pressure difference. But we could get some work from the mixture, because the pressure of the mixture is above atmospheric pressure.

The ideal gas laws and otto cycle thermodynamic laws are certainly quite solid. However, if you start mixing different substances, some of the implications will be different.

Third ---

You must consider that there are other implications to efficiency then just pressure and temperature. You must consider the efficiency of the compressor and expander devices. If adding water to the compressor makes it more efficient, it may more than offset any peak temperature considerations. If you can make the compression isothermal by adding water, than the efficiency of the overall system may improve.




RE: water injection to gas engines

glueontop:

Yes the laws are poven and hold in the controlled conditions in which they describe.  I don't have a NASA budget so my cars have to operate in the real world where the conditions that predicate the laws rarely exist.  In that case I trust empirical results and then seek explanations.  The presence of water at the wrong time is destructive (i.e. in the gas tank at the pickup) at the right time in the right quantities the presence of water mixtures have been shown time and again to be beneficial to intercooling and combustion - without negating any laws.

Studies have shown that while water injection will beneficially reduce maximum pressure it will increase BMEP and it is BMEP that matters in an Otto engine - not the max pressure - max pressure at the wrong point destroys engines.

RE: water injection to gas engines

Being pedantic here...
water actually contains an awful lot or energy.

e=mc^2

The trick is liberating that energy without the unpleasant side effects of nuclear bombs.

But, I'll grant you that water doesn't burn very well.

Sorry for the interuption everyone.
Please do continue, I'm finding this very interesting, (even if a lot of it is over my head)....

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

RE: water injection to gas engines

Hint:
The water droplet size at time of fuel ignition is my area of study. If in a pure vapor or large droplet form the effect will not occur. Power loss and emissions go up per the SAE tests. Possibly a water in oil emulsion with droplet size corrected is key. I am banking on getting it right in the intake plenum.

RE: water injection to gas engines

glueontop

The flaw in the combined gas laws and otto cycle theories as applied here, are not flaws in the laws, but rather the interpretation that they apply absolutely to the caes of water injection.

The flaw is that you are interpreting this as gas only. The water is injected in a liquid phase, and changes to the gas phase. Latent heat of vaporisation and expansion from liquid to gas are both involved, and not covered by the gas laws nor the otto cycle.

Also, no one is argueing that the water should be added to the tank, as this will cause corrosion, will be erratic in it's supply unless a very stable emulsion is formed, and will lean off the mixture by the amount of fuel it displaces, unless the fuel calibrating system is ajusted to compensate.

The water injection systems being discussed are the type that adds water to the airstream, independantly of the fuel supply system.

As already stated (by SBBlue I think), the water does not increase the peak preassure, but it tncreases the mean effective pressure. If the peak pressure is to high it destroys engines. As I keep saying, the main benifit of water injection, is that it helps to stop preignition and detonation (the results of excessive cylinder cylinder pressure and or temperatures). It can help to control the pressure build up rate to better match volume increase or piston speed as the piston travels over TDC and down the stroke.

bvicknair

I expect that water partical size, airspeed (shear), relative humidity, compression ratio, temperature changes within the manifold, and time between water discharge point and ignition will all impact somewhat on how much water evaporates and where it happens.

Regards
pat

RE: water injection to gas engines

obviously the ideal-gas law doesn't apply on the compression stroke, where we have a liquid/gas mixture but after the explosion on the power stroke.

SBBlue.. I don't have my tables at hand, but I can see a mistake in your calculation. You consider the water to be in the steam phase at the start. You don't take into account the heat needed to bring your water from about 50C to the boiling point and the heat of vaporisation wich will bring your mixture much below the temperature  you have calculated. That needed energy will be taken from your air and will probably lower its temperature a couple hundred degrees. Then you can use your table to make your calculations. If you remove a margin for the lost of temperature trough the engine block, you will end up with less energy then you had at the beginning.

It is not true that the otto engine can be compared to a gas turbine. There is a major difference that makes it possible in a turbine but not in a Otto engine. The gas turbine is a continuous process where the water as the required time to expand before it reaches the expander. In the Otto cycle, the power cycle appends so fast that the fuel/air mixture barely as time to finish to burn, in fact it continues to burn in the exhaust manifold. Any water you add won't have time to vaporise and expand before the begining of the exhaust cycle, it will then create back pressure and reduce power.

RE: water injection to gas engines

Glueontop. . . .

I purposely did the calculations that way to disprove your hypothesis about the ideal gas laws and otto cycle and show that it is possible to decrease temperature but improve efficiency.

I think if you do your calculations comparing equivalent power Otto or Diesel cycle engines to Brayton cycle engines you will find that air moves much faster through the Diesel and Brayton engines then it does a same power output Otto engine.

The proof is simple; the Otto cycle engine is essentially stoichometric; all the oxygen is used to combust the fuel. The diesel and Brayton cycle engines both run quite lean; there is much more oxygen than is needed for combustion. Hence, much more air is pumped through a diesel or Brayton cycle engine than a corresponding Otto cycle engine.

One other thing you are neglecting in your calculations is the effect of raising the temperature of the air during the compression stroke. Water is always steam above 700 deg F. Air reaches that temperature during a 7:1 compression stroke (I think -- I need to check the tables) and has a significantly higher temperature with higher compression ratios.

You may argue that there isn't time for water droplets to change to vapor, but I don't think you have any actual studies to support that assertation. There is certainly time for all sorts of chemical reactions to occur during the combustion stroke, so I don't believe that there isn't enough time for the water liquid phase to be changed to the vapor phase.

RE: water injection to gas engines

I have a book written in 1952 by a German engineer that used "exploding water" to hydroform precision pieces during WW2.

A more current publication dealing with the subject is 'Newtonian Electrodynamics' Peter and Neal Graneau. See Ch. 6-7.

Pressures routinely reach 20,000 ATM in water explosions.(290,000psi) The source or the anomalous pressure is currently under debate.

bv

RE: water injection to gas engines

I just got referred to this thread by a friend and being a long time user of water injection thought you all may be interested in what I have personally seen over the years.  I run a twin turbo, now EFI (was carb), twin turbo 340 Mopar in a 70 Cahllenger, strictly street, 14 psi boost, intercooled.

I use an old Edelbrock Varijection system that has been altered for instant on under boost conditions at 7 psi. It varies the amount of water based on rpm and absolute manifold pressure. It does not have adequate pressure to spray directly into a pressurized intake manifold, so I spray directly on the turbine blades. The turbos are lower than the inlet ducting to the throttle body, so even if I have a valve failure, I cannot water slug the engine.  I have run this system for over 15 years on carbed and EFI turbo engines, and would not go without water injection. I can run 8 to 1 compression at 14 psi on 92 octane all day without worrying about detonation.

I find the talk about atomization, hummidty, where the water evaporates, etc to be very interesting, as I have watched my system extensively over the years.  When I spray on the turbine blades, the water (with 50% isopropyl) vaporizes instantly, before it even touches the blades.  I have 50K mile turbos that show no erosion at all, and even the intercooler does not get any significant amount of moisture in it.  The ductwork all stays dry.  The low pressure area at the turbine inlet easliy evaporates the water spray.  I found no difference with EFI or blow thru carb in this respect.

When I was running a suck through carb setup, I was spraying directly into the carb throat with the water, and found that the carb venturi would vaporize the water right along with the fuel from the venturi.  Subsequent running through the turbo also further atomized both elements.  All was good unless the inlet ducting was cold enough to condense out the fuel and slug the engine.

In an N/A engine, you would spray straight into the carb with most systems like a Spearco. An Aquamist you could go into the manifold below the carb as they atomize better, but most folks don't do that. Unless you are dumping very large amounts of water into the carb, it will atomize, if it did not, it would build up in the intake and give a big slug to the engine when you turned, etc, and probably thermal shock or hydraulic the engine to distruction.  I think it would be a very risky business to try to get, or count on getting unvaporized water into the cylinder.

As far as the power is concerned.  As I mentioned before, my setup is instant on, off a pressure switch, or an override switch in the cockpit.  I have done lots of testing at boost levels to 12 psi (max without detonation without water) with the water on and off.  I give people rides and turn the water on and off, then off and on to see if they can feel the accelleration rate change.  I can tell you that no one has ever not been able to tell that the water came on and the accelleration rate increased.  It is very significant.  I would be surprised, however, if you would be able to readily feel the difference in an N/A engine, as when I turn the water on and off while holding the boost down with the throttle, I cannot feel a difference at all, in my low compression engine.

My net conclusion is that on a boosted car above 10 psi, water injection is necessary if you want to be able to run decent compression, timing, and mixtures, plus you will get more power do to charge cooling, even if you are intercooled.  On an N/A car, I would use water only if you need it to kill detonation because of high compression, bad gas, etc.  I don't believe it would give you enough more power to notice.

RE: water injection to gas engines

At 12:1 CR water injection I found makes a big difference on with high compression N/A on load.

From a direct causal effect - water injection is solely for suppression of knock.

The following is predicated on an properly implemented water injection system.

The great part of WI is the freedom you have tuning once the knock is effectively suppressed.  You are now free to run maximum power AFR on performance engines and maximum economy AFR on commuter engines.  Additionally whereas even when ineffecient fuel dumping was being used to suppress knock it was still difficult advance timing to MBT prior to overcoming the excess fuel and getting knock anyway, with water injection at optimal AFR levels you are able to always advance to MBT.

I am aware of only one other person who has injected prior to the turbo and he found that the wheel was pitted as a result - though he admits his jets likely were not sufficiently atomizing the water.

There is a discussion at www.turobice.net/forum/ (a noncommercial forum) and this very question is being asked - can water be safely injected prior to a turbo and it would seem your experience would indicate yes.  If you don't mind passing your story along there, it would be of benefit to those discussing that topic.

Ed.

RE: water injection to gas engines

Thank you Turbododge
It's good to see another contributor who actually knows what he is talking about

Regards
pat

RE: water injection to gas engines

Pat!

What you said about the water injection system used on aircraft engines is true. It is called an anti detonation injection system (ADI) and that is exactly what it is. At take-off power settings, particularly in hot weather, a richer than best power A/F mixture must be used to prevent detonation, with the excess fuel used as a coolant. With ADI the water and alcohol mixture is injected into the air stream and act as a coolant. The alcohol is added to prevent freezing. As the mixture is injected a de-enrichment valve opens and leans the mixture to best power setting.

This system is mostly used on larger radial engines - 2000 BHP and greater. On one chart I have there has to be a reduction of 30 BMEP and 5”Hg of manifold pressure with system off, so it makes quite a difference. Overall as much as 15% may be gained by this system on these engines, but they are air cooled with aluminium cylinders.  

Using water injection does give other benefits to engines, particularly from a cleansing point. Even the compressors on turbines are sometimes washed by spraying water into them while they are turning. As far as using this system in a street car I think you would might end up with a net loss in power because you have no means to adjust the mixture and detonation is not that much of a problem.
.
As to the question of which is heavier, dry vs humid air, you are correct in saying that you get more power in dry air. It shows up on piston engine power charts (up to 3%) and must be corrected for, although for an engine in a vehicle being driven you get lower drag and will cancel part of engine power loss. The reason is that water vapour is a gas, which has more hydrogen molecules (which are lighter) than air does, and these hydrogen molecules replace some of the molecules in the air. By Dalton’s law of partial pressures the measured total pressure is the sum of the pressure of dry alone and the pressure of the water vapour alone, and because the average density of air with water vapour is less than that of dry air, at the same pressure and pressure. Hot air can hold more water vapour and therefore a hot humid day has the most effect. I have a formula to determine the reduction in density with increase in humidity it you need it.

Cheers

RE: water injection to gas engines

Turboice:  You are absolutely correct in that one big factor with water injection is killing the detonation to allow you optimize other conditions.  It is very common in the turbo crowd to try to drown the detonation with extra fuel, even down to 10 to 1 A/F. All it does is cost power and give minimal results.  The is a very good chart in the Hugh MacInnis book Turbochargers on the affects of water on detonation, boost level and air fuel ratio.  One look at the chart and you can become a water booster for life.

Concerning the non erosion of my blades, it may have to do with the fact that my water only comes on when I really need it, so it is on a very small % of the time, but I am also very carefull to send the nozzle stream (it is not atomized) at the CENTER of the compressor shaft so that any impact is on a slower speed, less critical area, and the water flow moves out the blade rather than impacting it. Also, with Varijection, there is less water at lower rpms and boost levels and more at higher speeds and boost.  A single output volume, set to deliver enough water at full load, like a Spearco, can easily overwhelm a turbo spinning at lower rpm and impact the blades harder.  With the EFI controlling spark and A/F (12.5 A/F under boost)and careful tuning of the water we normally will only use a gallon of water per 1 to 2K miles of street driving, as we are good to 10 psi very safely without any water, (and 12 if the gas is good).  So putting is enough water to get to 14 psi is pretty easy.

RE: water injection to gas engines

Aviat - the benefits in tuning performance automotive engines is very similar.  Knock is a very large problem for forced induction and high compression normally aspirated engines.  The OEM solution is usually to throw fuel at the problem - which first is a very inefficient coolant low specific heat and secondly as Glassman proved excessive fuel (rich settings) inhibits the oxidation of CO which releases a large amount of the energy released in hydrocarbon combustion.  Now on your average commuter car you are generally running leaner than optimum power anyway - but here water injection can be used to run at optimum consumption instead.  There are many methods available to automobile tuners to modify the OEM fuel and timing settings to take advantage of water injection - for my car alone there are no less than a half dozen tools I can use to adjust fueling and timing.

turbododge - I need to get the MacInnis book since it is a new reference and I have collected a dozen or so other books for even the smallest reference to water injection.  Sir Ricardo also has a great chart that is very telling as to why water injection is the optimal tuning tool as opposed to what Corky might throw out there in pop literature with no basis and no peer review.  Sir Ricardo's chart is in my paper on water injection which I referenced above on October 1st (http://www.turboice.net/?documents/turbowhitepaper/titl...) and also linked in the FAQ I have written on WI.

RE: water injection to gas engines

In the 70's and 80's, I saw a number of suck through turbo combo's that injected before the turbo.

I have seen a system where the boost pressure was fed back to the water bottle, to boost the pump pressure under boost.

The idea of water damaging the blades was not considered in wet or suck through systems, as the fuel also impacted the blades, so the turbo was robust enough and slow enough to not have a problem. In those days hotrodders adapted turbos originally designed and built fot diesel truck engines. These were very HD with no real consideration for lag.

I was advised against useing a before turbo injection system on a turbo system which was OEM on modern EFI, high performance sports coupe (Toyota 7M-GTE). The advice given by some turbo tuneing specialists was that in their experience the water did impact on the blades and as the Turbo was a modern high speed lightweight high performance design, the blades would be lightweight and not robust enough to withstand the constant water impacts.

I took the advice, but also discovered that knock was not the limiting factor re boost levels with the stock engine, as fuel cut limited boost to about 9 to 10 lbs. It did not knock, even on normal unleaded at this boost.

As I took the advice, I cannot comment on it's accuracy.

Regards
pat

RE: water injection to gas engines

I have no evidence of this but my other concern besides the lower mass of today's blades is their balance.  If you have ever seen a turbo balanced you know that at 20,000 rpm very small changes in mass can alter it.  I would be concerned that any inconsistency in the spread of the liquid mass would throw the cartridge out of balance and cause undue stress on the bearings.  With so much success injecting after the turbo, I have never felt compelled to test out the blade damage theories or my own dreamt up issue of balance - which I hope has at least some merit.

Ed.
www.turboice.net

RE: water injection to gas engines

Turboice:  I can't seem to get off the home page on the reference site to Sir Ricardo's information.  Don't know why.  It very well could be the same information as MacInnis, as many of these guys reference each others work, except Corky who just spouts unfounded and often untrue opinions (my opinion of his info).

The erosion of the blades discussion is very interesting, and may apply to others differently than me.  I am running plain old T04, oil cooled turbos, and have been for many years. The newer turbos with the aforementioned lighter blades and perhaps more brittle alloys may be more of a problem.  With those I have no experience.  There was a post that mentioned someone who had a friend who did get blade erosion (post probably gotted whacked because it referenced another site).  Was this person, by any chance, running a water/methanol mix in his system?  From what I have seen and heard, methanol will take out turbine blades, throttle body plates and bearings, and can even corrode the tips of fuel injectors enough to cause pattern problems.  That is why I use Isopropyl in mine.

RE: water injection to gas engines

That Ricardo graph is very interesting. If you look at the sfc trend it /seems/ to be decreasing at very high bmeps.

Does anyone have a good explanation for this? Is this the steam engine effect, where the expansion of the additional gas (steam) late in the stroke is thermodynamically better than raising a smaller mass of gas to a higher pressure, earlier in the stroke?

If this is a real and useable property then it could give a motor whose efficiency graph has two sweet spots, which might be very useful for an economy car.
 

Cheers

Greg Locock

RE: water injection to gas engines

Wow, this is great, the discussion reminds me of the german WW2 aircraft that uses water mixed with alcohol to enable the engine to have higher boost during take off.

The water cools the charge and thus making the engine less likely to detonate. The alcohol on the other hand supplies more fuel (with higher RON rating) and maybe oxygen (correct me if I am wrong) for the combustion.

RE: water injection to gas engines

Methanol may be used instead of water. It supplies additional oxygen and also have higher octane rating.

RE: water injection to gas engines

Not exactly water injection, but Gunnarman (sic?) claimed significant dissociation of the water with his A-21/A-55 Naptha/Water emulsion fueled SI engines, thereby reducing the amount of air required to achieve stoichiometry.  

I find this a little hard to credit but any can anyone clarify (preferably someone with hands-on expereince with the technology)?  

RE: water injection to gas engines

By way of introduction this is my first post over here. I am the hotrod turboice mentions in credit on his web site, but had to change my handle slightly as it was already in use here.

Turboice: In ref to your comment.

The erosion of the blades discussion is very interesting, and may apply to others differently than me.  I am running plain old T04, oil cooled turbos, and have been for many years.


Seems I recall a reference I think in the NACA papers that mentions that blade erosion is not a concern provided the water mist does not exceed 10% of the mass flow. In the military fighter aircraft they injected some of the water on some configuration directly into the "eye" of the compressor.

Given the effectiveness of high pressure water cutting jets it makes perfect sense that it would be highly dependent on droplet size. If you've ever been on a motorcycle in a rain storm you have an intuitive feel for the effect.

I will look around and see if I can find that ref and double check the configuration.

Years ago we used to trickle water directly into the carburator primaries at a fast idle to blow out some of the carbon and as mentioned above when the water passed through the venturi you could see the shear forces tear it apart.

Turbododges experience makes perfect sense with hub injection.
You could maximize his technique with a small modification (may not even be necessary). Years ago I worked in a ceramics operation machining raw ceramics prior to firing. They made extensive use of carbide tooling and we sharpened it on diamond imbedded wheels. The wheels were shaped like a shallow cup with the grit on the outer face of the cylinder. To provide cooling water a very small drip of water was applied to the interior of the cup. Centrifugal force spread the water to a very thin film and it followed the front face and the was slung off as a microfine mist. I presume the same effect is taking place on turbododges compressor hub. The radial velocity of the center shaft and nut is probably slow enough you get no erosion but simply blast the water into ultra fine drops with brute force.

On researching water injection I also stumbled on another reason why methanol (or any alcohol) mixed with the water will help performance of a plain water injection system.

If you go to the major spray nozzle vendors and look through their catalogs you will see that droplet size of spray nozzles depend in part on the surface tension and viscosity of the fluid. Alcohol has a significantly lower viscosity than water and lowers the surface tension so all else being equal a spray nozzle running a Alcohol/water mix should produce a smaller mist droplet.


The spray droplet size also depends on the density of the fluid the spray is being injected into. The mist from a nozzle into a supercharged intake at 2 BAR pressure would be significantly finer than the same nozzle sprayed at ambient pressure. In effect the nozzle effeciency should go up as boost pressure increases.

Larry

RE: water injection to gas engines

After searching around a bit I found the reference I was thinking about. It was not in the NACA reports (although they may also contain the same info)

These refs all pretty much say the same thing, that the WWII  aircraft engines in many cases injected both fuel and ADI fluid into the "eye" of the supercharger compressor. The first three have some interesting additional info in them as well.

Here's a brief extract from the first.

http://www.unlimitedexcitement.com/Griffon%20Budweiser/Rolls-Royce%20Griffon%20Engine.htm
Induction was by through a huge Bendix-Stromberg PR100B4 injection carburetor, originally used on the Pratt and Whitney R-4360 radial engines that powered planes like the B-36 bomber.  The carburetor measured the air entering the engine, and provided metered fuel which went to fuel injectors directed into the eye's of the intake impellers.  ADI injectors were also co-located with the fuel injectors.


A control increases maximum boost when ADI is active.  The automatic boost control also incorporates an additional control which energizes ADI when a predetermined boost pressure is reached.  The ADI injector is incorporated into the throttle body, ADI being directed into the eye of the supercharger.  Finally, an injector incorporated in the throttle body directs fuel into the eye of the supercharger.



Turbocharging the Griffon:

Rolls-Royce carried our research into a turbocharged Griffon under a contract from the British Air-ministry in 1948.  The RGT.30.SM Griffon used a GEC turbo-supercharger, and was intended for a projected Supermarine long-range flying boat and as an upgrade for the Avro Shackleton.  At sea-level the engine had similar performance to the Griffon 57/58, since a wastegate was partially opened, limiting SL boost to 25 psig when used with ADI and preventing detonation.   Altitude the wastegate closed however, routing all exhaust through the turbine.   The interesting thing about this engine was the turbo was not staged with the supercharger, but instead the air pumped was used to cool the exhaust pipes and turbine, with the turbine also driving the supercharger through a free-wheeling (one-way) reduction drive.  This engine configuration is really a compound engine -- the turbine is used to recover exhaust heat energy and deliver that power to the crankshaft.  It was not used to increase the pressure ratio of the induction system.

http://www.unlimitedexcitement.com/Pride%20of%20Pay%20n%20Pak/Rolls-Royce%20Merlin%20V-1650%20Engine.htm
http://homepage.ntlworld.com/jimbonet/blowing.html

http://user.tninet.se/~ytm843e/engines.htm
http://www.home.aone.net.au/shack_one/rolls.htm
http://216.239.39.104/search?q=cache:BQ7YtGdb8A0J:www.fourthfightergroup.com/eagles/ma648.html
http://www.fuelcat.co.uk/history.html
http://www.worldhistory.com/wiki/W/Wright-R-3350-32W.htm        <-------- Bendix Stromberg PR-100 Injection Carburettor

Larry

RE: water injection to gas engines

I didn't read through all of these posts.  But as far as I always understood, water injection's main purpose is to lower combustion temps.  In doing so it allows you to advance timing and compression ratio which produces more hp. Water injection can replace EGR with a similar result.  thats the simple explaination as I understand it.  Molecularly, your dilluting the amount of oxygen in the air kinda like EGR does.  Water is fairly stable and doesn't add to combustion temps.....just takes away... therefore giving you lower combustion temps.. I dont know if Im way off here, but its what ive been taught at an engine builders level, not an ME level.  

RE: water injection to gas engines

JRW261

Your partly right, but there is more to it.

The liquid water displaces very little oxygen, so does not really act like EGR in that regard.

The water evaporating during compression and combustion will absorb some heat.

The steam generated during combustion will produce some pressure, and thereby heat. The guys good enough on thermodynamics tell me it gives a net increase in cylinder pressure.

At elevated temps during combustion, the water dissociates into hydrogen ions and hydroxyl ions.

These hydroxyl ions catalyse the reaction of carbon monoxide and oxygen into carbon dioxide, so accelerating the final phase of the conversion of hydrocarbon fuel into carbon dioxide and water.

A lot of this is from Turboice's website. I think he has a FAQ on the subject as well.

Regards
pat

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: water injection to gas engines

In the induction section of http://waterinjection.info/documents/turbowhitepaper/waterinjection.htm

"As the water absorbs heat the droplet sizes will decrease and the surface area of the water droplets will increase"
quoted from
 
This doesn't really make sense to me.  As a substance absorbs heat, its internal energy increases causing higher vibration and expansion.  that supports the surface area increase. I guess what I am saying is that the sentence contradics itself, or am I miss understanding it?

does it mean, the amount of droplets will increase, thus surface area increases, but individual droplet size decreases.... i guess that makes sense, is this what is ment?

I see where my explaination faltered.... water displaces air in the induction... which it does... however the water absorbs intake air heat causing a more dense intake charge, which overcomes any displacement the water originally cause and actually increasing intake air volume.

I know understand better, thanks.  Did I figure out the answer to my first question regarding droplet size and area changes?

RE: water injection to gas engines

water vaporizes in the the cylinder. I'm not sure you can talk about surface area of a vapor.
The vapor certainly dilutes the charge, exactly as egr does.
The only issue there is reletive amounts.
The catalyzation? no idea.

jay

Jay Maechtlen

RE: water injection to gas engines

JRW261

All other factors being equal, as the water evaporates, it will form smaller drops, but I expect no more drops, therefore the surface area of the drops will decrease in absolute terms, but will increase in relative to mass of water terms. The outside factor will be shear on the drops due to motion in the inlet tract and compression and early parts of the power stroke. Also, water will collect on the walls and floor, making very large drops or puddles, so who knows the net result.

The cooling increases the density of the air, not the volume. The volume is virtually constant as it is defined by the dimension of the manifold, which only changes a few thou due to temperature changes of the metal. As you have higher density and similar volume, you have greater mass.

Water has a significantly lower evaporation rate than petrol, therefore, I would expect most of the evaporation to take place as the heat rises during the early stages of combustion, with very little occurring before the inlet valve closes.

The volume of liquid fuel and water vs volume of air is insignificant re volumetric efficiency, unless you are using nitro methane in high proportions.

JayMaechtlen

I agree pretty well with what you say, and any water vapour in the inlet tract will displace oxygen, but I feel there is very little volume in the liquid form, and only a small amount of evaporation before the inlet valve closes, then it cannot displace any oxygen.

Regards
pat

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: water injection to gas engines

The velocity of the induction charge makes it not only unlikely but improbable that there would be any accumulation on the surfaces worth mentioning.  When you start talking about 150 g/sec of air on the low end it is unlikely that a few percent by mass of water will accumulate in the induction track.  Keep in mind that water injection is not a spicket of water sprayed into the intake tract it is a couple or a few percent of the induction charge by mass or volume.

I would expect water droplets to change in size and number as they under go shear and also balance out in equilibrium temperature and humidity.

I would not be surprised if several sentences are not worded entirely correctly - something I will seek to correct in edits.

As for mass displacement here is a good link that goes over that topic - http://not2fast.wryday.com/thermo/water_injection/opt_mass.shtml

Net/net you should not expect any "displacement" of air or oxygen from your induction charge.

Also due to other improvements that the cooling of the charge and valves brings to VE there is likely more oxygen available at spark ignition than there would otherwise be.

While water in combustion will enter and leave other phases it is water on the way in and water on the way out.  Other than lower EGTs I would not expect the water to have any other effect on the energy release of combustion.  The real benefit of water in combustion is that it helps complete the combustion process by improving the oxidation of CO, the complete oxidation of the CO will release more energy during combustion translating into increased torque.

Sorry that my language is not always technical as I am not an engineer by training and my recollection of physics and chemical terminology is not complete.  Though I am pretty confident I have a grasp of the concepts behind the terms and that is what I try to communicate.

Ed.
www.turboice.net

RE: water injection to gas engines

Pat:
"... and any water vapour in the inlet tract will displace oxygen, but I feel there is very little volume in the liquid form, and only a small amount of evaporation before the inlet valve closes, then it cannot displace any oxygen."

In terms of limiting the amount of air-fuel mix, that sounds right. We can probably assume that the water is mostly liquid (in small droplets) untill it gets into the cylinder and the compression stroke starts.
As the mix is compressed and the water finally vaporizes, then it will act to dilute the charge (like EGR), won't it?

regards

Jay Maechtlen

RE: water injection to gas engines

JayMaechtlen

Good point, it will dilute, but not displace. I was presumeing you were useing dilution for displacement, as this is a very common missuse of dilution.

I still don't think that the water vapor dilution has the same effect as EGR dilution, as wth water disociates and takes part in propagating some of the oxidation of the fuel, but then again, exhaust contains a fairly large portion of water. I need to think about what the carbon dipoxide in the exhaust will do to the reaction. I expect that it just gets in the way at a molecule to molecule level, and slows the reaction a little.

Exhaust gas will not undergo a phase change, where as injected water will, and the heat absorbed and the potential volume increase will both affect the temperatures and pressures.

Regards
pat

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RE: water injection to gas engines

A couple of questions:

Why is the simulation performed at atmospheric pressure as opposed to some elecated pressure? What effect would that have on it's results?

Just how optimistic is 100% vaporization? This thread makes it sound quite unlikely, yet that link is highly dependant on that.

RE: water injection to gas engines

I am working on the same problem and would appreciate it if you could share your findings. I have a patent regarding pintle-regulated fuel and water injection that I am trying to model.

RE: water injection to gas engines

For most applications, water is injected to cool the intake charge, and thus, aid in increasing power. Water is used to suppress detonation caused by high temperature and pressure developed within the combustion chamber (usually) when the effective compression ratio has been taken beyond the auto-ignition point by either a turbo or a supercharger.
Water, with its high latent heat content, is extremely effective for controlling not only the onset of detonation but also the production of oxides of nitrogen in the modern leanburn engines.

RE: water injection to gas engines

I've read this thread with great interest and would like to add my tuppence-worth.
My late father was a big fan of water injection on his Mk1 Honda Prelude track cars. One of these ran a turbocharged 2.2 Accord engine (very expensive to build and damned unreliable) and the other a supercharged 2L that he got from the breakers and bolted an Eaton Blower straight on without much in the way of anything else. (Much more fun to drive than the turbo, pulled like a train from idle)
Both were fitted with modified Edelbrock Vario water systems, though I can't specifically remember what we did to them at this point.
The turbo knocked like hell if the water tank ever ran dry, leading us to believe that we had a touch too much compression for the boost we were using, but was spot on with (about) 1.8% water/methanol.
The supercharged one didn't seem to care knock wise, but definitely pulled a little more strongly with the water on.
I've also had a 2.3l Saab 9000 Turbo (someone set fire to it when I was working away!!!) which is controlled by an Automatic Performance Computer - APC, that limits the boost with reference to a knock sensor (and other stuff.) I had a Spearco setup on this and can definitely attest that the electronics would give you 1-2 Ibs more boost with the water on than without.
Although I agree with Patprimmer that the real benefit of water injection is to make up for lack of fuel octane and excessive compression, based on my experience with the turbos, I do wonder whether there might not be some other factor at work based on the supercharged engine. I'm building a hotrod at present with a Supercharged Mitsubishi 4G63 2.0, so I intend to slap on a Spearco or similar and check the effect on that.

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