Water injection in a jet engine increases performance in two ways. One is the reduction in compressor outlet temperature allows for more fuel to be burned without melting the turbine. Two, the increased mass flow from the weight of the water will boosts the thrust.

I was thinking it could go either way. I'm surprised that an air density twice normal would be more pressure than the heads could handle. Don't the pressures during combustion get pretty high? Of course, there's a piston waiting to be moved downwardly by those pressures whereas duing the compression stroke, the heads can only sit there and take it.

What is the ideal level of compressed air (turbo or super) that a 617 can take? This might be toughy to answer. Then again, it is no doubt known what sort of air pressure a 617 turbo is dispensing.

__________________
1986 300SDL, 362K
1984 300D, 138K

After thinking it over again, I believe you are correct. When the turbo is running, the absolute pressure in the cylinder can get up to 26.5 psi, which is very close to twice the normal density. I'm quite sure that you could dial up the boost to enable 29 psi without any consequences to the head gasket.

As for "ideal level" of compressed air, I don't think there is an answer to that.
The more air you give a diesel, the more fuel you can give it and the more power it will give you. The risk is too much heat and a melted piston.

So, the ideal level of air would be the amount of air that would be just shy of melting the piston when a proper amount of fuel is delivered to that air. It's a delicate balance, one that the manufacturer must stay safely away from, because the conditions are highly variable and he must protect the engine from the worst possible condition.

There are several fellows who have bumped up the boost and the fuel on the 617, without an intercooler, and have had no issues. Of course, watching the exhaust temperature becomes a vital task when maximum power is utilized.

Interesting stuff. Part of why I ask is that I have a fantasy invention that will provide cold, compressed air for combustion and the level of compression would have to be controlled of course. Since a cooler initial temp of the air being sent to the cylinder will lower combustion heat and protect the piston, I'm thinking that if you could deliver air at say 0 Fahrenheit that was also, say, double atmospheric pressure like we're talking about, you would have nifty power considering that air that cold is going to have more oxygen per cc than hotter compressed air.

It's an ambitious idea, maybe too ambitious, I don't know. If you want to hear more, I'll e-mail you. I don't want to let this million dollar idea out to the general public. (yeah, right)

__________________
1986 300SDL, 362K
1984 300D, 138K

It's a fabulous idea. The current crop of intercoolers will deliver air at temperatures that are about 40°F. above ambient, so the cylinder gets 120°F. air on an 80°F. day. The engine makes good power with this air.

Now, if you could deliver 0°F. air to the engine, you could really dial up the fuel and make some serious power.

But, short of taking dry ice on board with you, how are you going to get the air (lots of it) down to 0°F? Remember, it has to be useable for daily driving.
Runs at the racetrack for 1/4 mile don't count.

I believe it's conceivable for a liquid to air intercooler (L2A) to [under the correct circumstances, e.g. running in a bath of ice water] deliver ambient or slightly sub-ambient charge air temps, but that's not practical for daily driving, just the track.

Hey, you could always plumb an A/C evaporator into the intake manifold...

..........damn condenser can't even keep up with the air inside the cabin..............imagine trying to keep up with 4500 litres/minute.

Ain't it the troof?

A couple of years ago somebody (I thought it was Zeitgeist) posted a link to a website in which a vortex was used to separate hot gas molecules from cold ones. Darned if I can remember what it was called.

If somebody doesn't name that device, I'll have to resort to an internet search.

B

Twasn't me, I disavow all knowledge and discourse regarding such shameful alchemy and snakeoil.

Sorry H2O2, didn't mean to imply snake-oil-manship. It may not have been this Forum. May have been one of my kuh-razy brothers.


Bot

It's called the Hilsch Vortex. I remember a lab experiment when I was an undergraduate involving one.....many years ago.

__________________
Lawrence Coppari

2002 SLK32 AMG
2005 Acura TL
1987 328GTS
1986 944T

Hilsch Vortex, eh?

http://www.visi.com/~darus/hilsch/
http://www.montagar.com/~patj/hilmnu.htm
http://www.airtxinternational.com/how_vortex_tubes_work.php

I know it seems crazy -- that is, how could I possibly hope to get that much cold, compressed air on board and have it at the engine's beck and call? It would use a process different than an air conditioner, but also involving compression and expansion.

I'll put together a thumbnail sketch of the idea soon.

__________________
1986 300SDL, 362K
1984 300D, 138K

Bot,
Thanks for the links.
I remember a Popular Science cover story from the mid to late 1960s that trumpeted, " Air Conditioner with No Moving Parts".
The article went on to explain the obvious benefits of a such a simple mechanism, and predicted its universal use in auto air conditioners in a few years. Well, I'm still waiting.
Forget the R12 vs R134a controvery, just hook me up with a vortex tube!

OK, Carl, we all will be waiting. Try not to violate the laws of physics too badly.