Diesel fumigation in the air intake

[Begle1]

I remember Loch over there on DFSDGRTTYRYERTY (can't say it) talking about how he installed a cold-start Diesel intake-injection system off of an older Mercedes in his truck.

How's that work? Anybody know how it's working for him?

If one could avoid preignition, wouldn't that effectivly counterbalance the VE's lack of fuel delivery at high RPM's?

How could one avoid preignition?

[meby]

Could you explain what diesel fumigation is ? thanks

[Begle1]

A member of another forum said that he had a Diesel mister spraying fuel straight into his air intake, before the turbocharger.

Considering that the limitation of our injection pumps is fuel at high RPM, if you can "carburate" fuel and bypass the injection, you could get around that weakness.

I would imagine that the major problem is preignition; having the fuel light up while the cylinder's still going up on compression. Which I do not know how is best to avoid.

[oldestof11]

A member of another forum said that he had a Diesel mister spraying fuel straight into his air intake, before the turbocharger.

Considering that the limitation of our injection pumps is fuel at high RPM, if you can "carburate" fuel and bypass the injection, you could get around that weakness.

I would imagine that the major problem is preignition; having the fuel light up while the cylinder's still going up on compression. Which I do not know how is best to avoid.

I think it would be dangerous in winter as the fuel passes over the grid heaters. Then you would need grids and anything else it destroys.

Jon

[Begle1]

That's a granted problem, but not too hard to bypass if you just didn't use the fumigation while it's warming up in the winter. Or if you just installed a manual switch on the heater grid solenoids.

[mhuppertz]

You don't want a coat of oil inside your intercooler because it KILLS the heat transfer ability. Diesel is a bad choice anyway because of the pre-ignition problems mentioned above. That's one of the reasons people fumigate with propane, because it is a high octane fuel and more resistant to pre-ignition.

[Begle1]

Oh man, my poor intercooler would never forgive me.

Propane would have the same effect, but it has crap for BTU content. And it's really dry, altough I'm sure Diesel wouldn't be too good on valves either. Not that big of an issue.

Propane's the equivalent of advancing timing. Under light load it's possible to go too far, but with some sloppy injecters at high RPM, I wonder how much you could get away with...

So the question is, what has high BTU content and really low cetane value... What about high octane?

[mhuppertz]

So the question is, what has high BTU content and really low cetane value... What about high octane?

Higher BTU=Lower Cetane value in most cases in hydrocarbon fuels.

The next higher BTU hydrocarbon is a WAX at room temperature! Parafin is a very high BTU/Low cetane fuel, just ask a candle!

[Begle1]

I think that cetane is correlated to auto-ignition temperature.

http://www.engineeringtoolbox.com/fuels ... d_171.html

#2 Diesel fuel auto-ignites without any open flame or spark at 494 degrees. Propane goes at 842, methanol at 725, gasoline at 536 (higher octane would probably be a higher temp; I don't know how much higher).

So the idea of propane and methanol fumigation is that they both have high enough autoignition temperatures to not light off on the combustion stroke; they only light off after the Diesel fuel is injected, burns and provides a flame source.

It isn't supposed to start the combustion any sooner on the degree wheel. When the fuel is fumigated, it disperses evenly amongst the entire combustion chamber. Typically, injected Diesel all burns in a stream focused in a bowl on the piston; the dense mist of fuel doesn't burn as thoroughly or quickly as a distributed mist. But if the Diesel fuel ignites something like propane, then the entire chamber combusts, aiding the burning of the Diesel fuel and adding some extra energy to the mix in the process.

I think gasoline's a bit too low on the autoigntion side to be safe. But if Loch really did fumigate Diesel fuel, and it didn't ignite so far before TDC that he beat his engine all to Hell, who knows what gasoline would do?

Well heck, they tell us to turn off our engines at the gas pump in order to avoid sucking gasoline fumes and going into runaway. When you such gas fumes, does it hurt the engine through massive timing knock and preignition, or does it hurt the engine through over-rev's?

It's possible to get timing knock with propane, too... I guess that's because the Diesel is injected slightly before TDC?

So ya'll know what the ideal fuel seems to be... Hydrogen has one of the highest autoignition temperatures around, has the highest BTU content of any fuel available and burns like a dream...

[mhuppertz]

Actually Hydrogen has a ver low auto-ignition temp, re: Hindenburg!

[Begle1]

No. The Hindenburg was set off when static electricity produced a spark.

Without a spark or open flame, hydrogen won't ignite until 932 degrees Fahreinheit. Diesel ignites without spark or flame at 494 degrees.

Since compression temperature is between the auto-ignition points for Diesel and hydrogen, the hydrogen will never burn until it is set off by the burning Diesel. The burning hydrogen then ensures the complete burning of the injected Diesel.

Anybody know the exact temperature that the combustion chambers get to during compression stroke?

[mhuppertz]

I stand corrected, you are right.

[meby]

so why not just do a water/meth setup? wouldnt this accomplish the same thing?

[Begle1]

Yes, as far as I can tell propane and methanol fumigations do the same thing, but methanol adds more power per volume. Theoretically, hydrogen and high octane would also do the same thing, but add even more power per volume.


The goal is to fumigate something with a high enough autoignition temperature, so it won't light off until the Diesel fuel is injected. The fumigated substance will evenly spread itself amongst the cylinder; as it combusts, it more efficiently burns air in the cylinder and ensures the burning of the Diesel fuel.

The reason you are limited in the amount of fuel you can fumigate into an engine has to do with the timing of the injectors; our engines inject fuel 5-20 degrees before top dead center in order to give the fuel enough time to burn. However, since the fuel starts burning on the compression stroke, the engine fights itself to reach top dead center, resulting in lost power and higher combustion chamber pressures (which leads to blown gaskets). Of course, if you were to wait until TDC or after to inject the fuel, it would make excessive EGT's due to afterburning in the manifold, smoke blue, waste fuel and even misses at high RPM's.

So, since we fire fuel before TDC, if too much fumigated fuel is present in the compression stroke, it will ignite too early; in addition to the inefficiency from fighting to turn over the engine, you will be causing excessive head gasket pressures as well as timing knock or preignition, which can be fatal to cylinders or hydrolock the engine.


So, the question is: what if we were to fumigate unprecedented levels of methanol, propane or high octane, and set the injector timing at TDC or close to it? Would the fumigated fuel be sufficient to alleviate the problems traditionally associated with such retarded timing?

[meby]

ok...I think I follow you now.