Explain water injection

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I cant honestly remember how the conversation started but it was about the dome on locomotives and as a kid the expression "dry steam" was so curious it stuck in my mind. It could have been at the York railway museum where they have all types anyway.
 
Maybe for a very short time at full rattle ....

Seriously, I'm not sure if you can have water injection and Nitrous at the same time, and don't really see why anyone would try. But is IS a good question. I'd think the mixture would go seriously lean unless you had a separate solenoid or other mechanism to compensate when each one was activated.
 

Since I spent some years working on rebuilding one of David Tallichet's Thunderbolts; I read, studied, consumed every piece of knowledge about the P-47 as I could. Dang and I remembered right!

In the P-47D-25/-35 handbook you'll find the schematic of the water injection system. Yes there is a derichment valve that decreased the amount of fuel to the engine under Water Injection. When you pushed the power into water injection range the derichment valve came in effect.

Remember most WW2 US fighters had lean/rich mixture settings until auto-mixture came out. This was used to keep cylinder heads cooler yes? I know the 13:1 ratio is perfect, but they ran fighter engines rich at high power settings and running rich to a point doesn't cause nasty things to happen. Wasting fuel yes, but it won't put holes into piston crowns like running lean will.

Now derichment would mean when you went into water injection that the mixture would need to be changed from the rich mixture setting that would be used at normal maximum power.
 
Believe it or not, Mad Max, the Tallichet guys are still around at Chino, and have a different hagar (closer to Merrill Drive on the east side). Joe Yancey is now taking over David's old hangars and is having them considerably upgraded with power and amenities. Soin there will be new baby Allisons coming out of there.

Also, they are just starting another hangar expansion. Looks like Chino Airport is staying healthy.

Cheers.
 
agree

With either system you are pushing the engine (aircraft engines anyway) into a borderline area and flirting with disaster. Trying to use both at once might be possible but adds to the variables and any variation at this point leads to engine parts all over the landscape.
 
Thorlifter said:
How does water injection provide more horse power? Is water actually being injected into the cylinders because to me that would hinder the combustion process.
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Water is injected, usually before the supercharger. It does two things
1 cools the charge which increases its density and thereby allows more air/fuel mixture to be drawn in. This works even without a supercharger.
2 lowers the temperature which prevents preignition and knocking and thereby allows a increased boost pressure that allows more air/fuel mixture to be forced in.

There may be combustion chemistry effects as well and the the water itself adds mass that expands. An alcohol is usually added to prevent freezing because intake manifold is at negative pressure and thus colder.

Normal combustion is at a stoichiometric ratio of 14.2 parts air to 1 part gasoline by mass. By making the mixture "rich" with fuel a substantial charge cooling effect is created by some aromatic fuels that has a similar effect to water injection, it also changes the combustion balance effectively increasing Octane Number. To take advantage of this the fuel needs to be injected where it reduces the work of the supercharger ie ahead of it.

The allies I think referred to it as ADI anti detonation injection. There is a story of some P-47 destroying their engine when ADI was turned on. Whereas the Germans switched from MW30 to MW50 in winter the P-47 were supplied with something equal to 30% ethanol which didn't work in high altitude Europe. May also have been the USAAF using isopropyl or butyl alcohol which probably wasn't authorized by Pratt and Whitney. For a while anyway P-47 pilots were reluctant to test fate and turn on their water injection.

When German Green dyed C grade fuel went from about 93/115 to 96/130 about late 42 or early 1943 the direct fuel injected engines like the BMW 801 received a method of injecting fuel into the supercharger "rich mixture injection" inlet to take full advantage of this.

Initially only ground attack Fw 190F received this, the fighter versions the Fw 190A series received increased boost only. I think 1.57ata in part because they operated at higher altitude where the supercharger was unable to overboost.

Eventually the two systems were combined.

The BMW801 didn't receive water injection, the so called Ribbentrop system till late war. There are some stories of water injection splitting or corroding cylinder heads. That may be false rumors from experimental direct cylinder injection which yield such results. I think at some point BMW began casting their cylinder heads in a vacuum, which may have increased their strength. Rich mixture injection achieved the same with less hassle.

I think the V-1650 of the P-51H combined rich mixture with ADI water injection.

Water injection also works with jet engines. Probably why some 1970s jets had Smokey exhausts.
 
vikingBerserker said:
Out of curiosity, could you have an engine with a supercharger/turbocharger, water injection and Nitrous Oxide?
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Jumo 213E1 on Ta 152H did that and they were run simultaneously. Remember this wasn't about increasing power but maintaining power at allude so they weren't adding mechanical or thermal stress so long as the oil and water cooler were sized so could get rid of the normal heat load in the thinner air of high altitude. Generally water injection was used at low altitude and nitrous oxide at high (above critical or full throttle height altitude) but there are no hard rules. Late war Fw 190 and Me 109 had a rear tank of about 140 liters which could take MW50, Cryogenic nitrous oxide, or extra fuel depending on if the mission was low altitude, high altitude, long range or whether the high octane C3 fuel was available. Usually not installed for multi use because of a shortage of the plumbing and valve system required.

British Night Fighter Mosquitos used Nitous Oxide to catch Me 410 at low to medium altitude. The Me 410 was elusive because of its speed, bomb bay and tail warning radar. Some P51 sent to patrol Me 262 airfields had it to help catch Me 262 in a dive.

The planed up grade to the Jumo 213EB achieved the same performance as the Jumo 213E1 on the Ta 152H but without NOX and at 4000 ft lower altitude. No idea if they were going to keep the nitrous oxide injection. Ta 152H is unique in being simultaneously equipped with both water injection and nitrous oxide (called a ha ha system because it was dental anesthetic laughing gas also GM-1 or Goering Mischung 1 because of his role in promoting it)

I have a feeling that nitrous oxide was a superior system but a hassle from the point of view of handling, storage. Probably 50% evaporated during transport, standby.
 
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The MW and NO systems in German a/c were to be used at different altitudes.

The MW for lower altitudes and NO for higher altitudes with the transition altitude the FTH of the engine.
 
US WW2 aircraft jargon usually called water injection (MW50) ADI = Anti Detonant Injection. This is actually a better technical description also of what it does!

To talk my high school chemistry water injection is a catalyst not a reactant? apologies to chemistry teachers
 

GregP,

That's good to know. The one I worked on was located at Air Heritage in Beaver Falls, PA and was sold to Butch Schroeder after David went on to the Blue Skies. Hairless Joe is the paint job on her. Gawd did I drill alot of rivets out on that hulking airframe. 8-0 It also has the biggest dang turbo that I've seen! It's hard to believe they were turning that thing just shy of 20,000 rpm.

Koopernic,

There weren't any problems injecting water into the cylinder of the 801 that I read of, but doing that didn't cool the air charge and in effect didn't keep the engine out of detonation. I would imagine they realized that when detonation broke something when testing it like pistons (more probable) or maybe heads.

Rich mixture did work, but only when injected into the intake eye of the supercharger. A couple of added benefits were no additional tank for water needed so saved some weight and no problems with corrosion.

The problems they had in England were the use of Isopropyl alcohol. Only Methyl or Ethyl can be used for ADI.

Best Wishes
 
The alcohol is there as anti-freeze, on a day when it is 59 degrees F at sea level (standard day) at under 8,000ft the temperature drops to freezing and at around 16,500ft you are down to 0 degrees F or about -18 degrees C. No aircraft was sealed up totally so you have some sort of airflow over the storage tank and lines.

It only really works on supercharged engines because un-supercharged engines don't have the temperature rise in the intake system that supercharged engines do. Without the water flashing to steam in the supercharger you don't get anywhere near the heat absorption. It takes over 6 times the heat energy to change water at 100 degrees C to steam as it does to raise the same amount of water from 15 degrees C to 100 degrees C. If the air in your intake manifold is well under 100 Degrees you are going to see very little benefit.

Heat flows through an engine, that is raising or lowering the intake charge temperature by 50 degrees will see a 50 degree rise or lowering of the peak temperatures in the cylinder and a 50 degree rise or fall in the exhaust temperature. This is assuming you don't change the amount of fuel burned, which was pretty much the point of using ADI, but helps point out why it worked.
This heat absorption of water was so great that the quantity of water used was much less than trying to get the same effect using either gasoline or alcohol and so was more efficient from a weight stand point despite water being heavier than gasoline or alcohol, even when mixed with alcohol as anti-freeze.
I don't believe the water (or alcohol) was actually a catalyst in a chemical reaction. I think the explanation is much simpler. For instance on the Corsair the use of water injection allowed an increase in manifold pressure of 9-12 % which, if the mixture was at equal density, would give about a 9-12% increase in power. In practice they got about 12.5% more power at sea level and almost 20% more power in high gear at around 20,000ft. But please remember that a sea level the the auxiliary supercharger was bypassed and the air was being compressed 1.9 times, at 20,000ft the air was going through both supercharger impellers, the auxiliary supercharger was in high gear and the air was being compressed about 4.9 times. It was much hotter/less dense than the air at sea level even with the intercoolers.

Air cooled engines were almost always operating closer to the edge than liquid cooled engines near full power and even back in the 20s had been called sever duty engines in regards to fuel while liquid cooled engines were called moderate duty.
 

Source for the MW 50 and GM-1 allowed to work in the same time? Ditto for same fuel tank that can hold fuel also being able to hold GM-1. Availability of C3 fuel have had no bearing on what the extra tank on the Fw 190 or Bf 109 will carry.



Again - sources please for the use of NO on Allied A/C at low and mid altitudes, especially on the P-51s?

Erich said:
actually the MW 50 was used at high altitudes in the AS 109's according to former pilots....
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The rated altitude was at around 8-9 km (depending on the ram) on the AS engines, so indeed they could put the MW 50 to a good use there. The AS engine called ASM when MW 50 plus fixtures needed were outfitted.
 
Benefits of water injection not directly mentioned beforehand is the reduction of Exhaust Gas Temperature (EGT). I mention it now from the point of some jets (like early KC-135's) using water injection. One is able to gain more power though the use of more fuel and rich mixtures with water injection being able to manage what would otherwise be overly hot exhaust that would damage turbine blades.

In piston engines, aluminum pistons melt at about 1220* F. Some alloys slightly higher. High sustained in cylinder temps will melt these pistons. Water injection goes a long way in moderating these temps.

Use of methyl alcohol not only has the benefit of anti-freeze, it also adds power by virtue of the extra combustible energy being introduced. 30-50% alcohol content being the sweet spot. No more than 50% however.

Nitrous Oxide can be used in conjunction with water injection as they perform two very different functions. I cannot speak to it being used this way in aircraft in WWII. In order for Nos to work, you have to have a fuel rich condition so the extra oxidizer has fuel to mix with. Otherwise you have diminishing returns or damage from too lean conditions. In auto racing we colloquially speak of Nos as "a turbo in a bottle".
 
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soulezoo said:
Use of methyl alcohol not only has the benefit of anti-freeze, it also adds power by virtue of the extra combustible energy being introduced. 30-50% alcohol content being the sweet spot. No more than 50% however.
.
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we are over complicating things. You need about 2 gallons of alcohol to equal 1 gallon of gasoline (Very roughly) as far as BTUs of energy go. Alcohol works in racing engines because you can burn roughly twice as much alcohol using the same amount of air. actually the ratio/s are in alcohols favor but the limiting factor in the aircraft engines was the amount of air flowing through them. under rich mixture the engines were getting plenty of gas, more than they could actually burn. They were blowing unburned or partially burned fuel out the exhausts.
Most engines using water injection cut back on the amount of fuel being supplied when water injection was used. The Corsair by 30-55 gallons an hour depending on altitude and supercharger gear in engaged. Water was supplied at about 25% by volume and 30% by weight. The amount of alcohol was small in proportion to the amount of fuel cut. Somewhere around 25% in heat value compared to the fuel cut?
 
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The article on water injection in modern motorsport engines, that is injection into the cylinders on turbocharged engines states it is purely to prevent detonation. Within that it is logical that all methods of tuning for power increase the tendancy for detonation. The water therefore allows a higher state of tune without the high temperature exchanging heat energy for a volume/pressure increase as water turns to steam/ superheated steam.
 
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