I May Be Wrong About Water Injection WRT Improving Fuel Economy

[teoman]

Hnm. Then how to easily approach those conditions? Without serious engine modifications?

Add diesel to gasoline to increase energy content? (And over here it costs less 4/5 ratio to gasoline) and then tame it with water?


Please correct me if i am wrong, these are my assumptions:

Warm air is less dense as the molecules have more energy they move faster, bump in to eachoter so take up more space. As ther is less o2, engine injects less fuel. So you reduce your effective engine size relative to howmuch fuel you can burn.

Warm air molecules, especially o2 move faster. So the chance that they bump in to fuel and combust is more likely. This increases burn speed. Burn speed is important for lean burn, because during lean burn when there is less fuel it burns much slower and you end up ejecting still slowly burning fuel from the piston which can burn the valves.

Warm air can also cause combustion of the fuel before the spark, this is not good at all beacuse the piston tries to move against the other pistons and something breaks.

Water gas has a much better expansion rate when they receive energy, this way they can generate more usable mechanical power from the combustion heat.

Water droplets when they evaporate with the combustion heat will cool the piston. This means lower combustion temperatures, so less energy is lost to the coolant.

During the compression stroke the water condenses in to droplets and the later evaporates. Some say that while they transform in to steam, they help the fuel vaporize and increase combustion efficiency.

The presence of water in the cylinder prevents detonation (or retards it). It also slows down the burn speed. The first thing is an advantage as mentioned previously, you can use lower quality or more energetic fuels, or increase compression to gain efficiency. The second part may not be so good as fuel may not have enough time to burn before exiting the piston. This has to be controlled or monitored so in my opinion a cylinder pressure monitoring system is interesting.

Steam injection. Not sure what to think of this. It will take more volume than water droplet injection that is for sure. It carries a lot of energy. When steam encounter cooler fuel, it will transfer its heat to fuel helping it vaporize. What will it do to detonation? No idea...


Please correct my assumptions if i am wrong. (These are for gasoline engines, not diesel, as they can run very very lean).

[seifrob]

This page: Aircraft Carburetors and Fuel Systems: A Brief History - 09 states water injection is for detonation controll.

(i had anecdotal evidence it was used in WW2 Spitfires for temporary boost, but so far no luck in search. So far it seems that water injection only controlls knocking??)

Ahh, posting too late. Never mind.

[oil pan 4]

That's just my hypothesis based on reading the only creditable sources I could find (reading about U.S. army air core ww2 piston driven engines in fighters and bombers).
I'm just trying to reapply what they were doing 60 to 70 years ago to on road use. Make a high compression engine, that uses water to control detonation under high load. Then lean out the air fuel mixture going into the engine to cruise along and get as far as possible on a load of fuel, not using water while cruising along, because water is heavy and takes up room.
That is how I'm going to try to do it. But I'm using a high compression engine, large but not insane cam, file fit rings. I have built the engine around this idea that should work. If it doesn't work I'm stuck burning premium gasoline all the time.
But if you apply what I'm doing to a production engine I don't think it will do anything. Of you have one of those hot euro, jap, or domestic engines that requires premium gas and won't run on regular it could work.
Hopefully t vargo can find something that works on production engies. If anyone can legitimately make it work or prove that it doesn't on milder mass produced engines he is our guy.

[cRiPpLe_rOoStEr]

Originally Posted by teoman

Warm air can also cause combustion of the fuel before the spark, this is not good at all beacuse the piston tries to move against the other pistons and something breaks.

Air temperature might be already more than "warm" once it starts leading to pre-ignition.

Water gas has a much better expansion rate when they receive energy, this way they can generate more usable mechanical power from the combustion heat.

Not sure if the expansion rate of steam would improve the conversion of the energy contained in the fuel to heat so much at all, since it ends up decreasing the dynamic compression.

The presence of water in the cylinder prevents detonation (or retards it). It also slows down the burn speed. The first thing is an advantage as mentioned previously, you can use lower quality or more energetic fuels, or increase compression to gain efficiency. The second part may not be so good as fuel may not have enough time to burn before exiting the piston. This has to be controlled or monitored so in my opinion a cylinder pressure monitoring system is interesting.

Ethanol has a lower energy content than gasoline, but it does have a greater resistence to detonation. So, would you consider it to be of a lower quality?

Anyway, since a lower amount of both the fuel and the supplementary water injection takes less latent heat from the intake stream, it doesn't sound so impossible at all to keep the temperature at a reasonable level in order to not disturb the flame spread

Steam injection. Not sure what to think of this. It will take more volume than water droplet injection that is for sure. It carries a lot of energy. When steam encounter cooler fuel, it will transfer its heat to fuel helping it vaporize. What will it do to detonation? No idea...

Steam carries a lot of energy that had already been turned into heat. But it might be beneficial only as long as both the temperature and air relative humidity are low Otherwise it would be more of a trouble.

[t vago]

While trying to model the final temperature of the intake manifold after hot water is injected, I came across this paper. Interesting read.

Osaka City University, Dept. of Urban Engineering, Osaka, Japan: EFFECT OF WATER TEMPERATURE ON EVAPORATION OF MIST SPRAYED FROM A NOZZLE

[teoman]

That was an interesting read, thanks for the link.

Those systems have started to appear over here as well. Best to stay clear of them if there is a risk of legionella.

[t vago]

I think I found the mechanism by which the hot-air intake works.

I am going to push forward with my testing. If my hypothesis is correct, I should see an FE gain of about 4% to 5% due to the addition of heated water.

[teoman]

What parameters will you be heating the water to?

And how do you plan on injecting it?

[t vago]

Originally Posted by teoman

What parameters will you be heating the water to?

And how do you plan on injecting it?

I plan to pressurize my water to about 45 psig, then heat it up to around 200 F. After that, I plan to inject it into the intake, probably after the throttle body.

[teoman]

With an injector or orifice?