dieseling a gasoline

[beef_bourito]

Would there be any benefit to diesel a gasoline? so run high compression, high boost, inject the gasoline when the engine is close to tdc. would there be any disadvantage?

Also, what about running the engine without spark plugs, basically run on knock?

For the second thing, i could see a problem with getting the fuel to ignite because of the different knock dentencies at different rpms and different throttle positions. with a variable compression system would it be possible to change the compression and boost so that you can have knock around tdc so that you could start the engine, then it would adjust the compression ratio and boost controller so that you could run part throttle (high boost, high compression) and run at full throttle ( low compression/boost).

I was just wondering because if you ran a gasoline like a diesel couldn't you get the gas to burn much faster because of the higher heat, also you could desing an engine to run for high torque if you lengthen the injection stage to get it to burn through the whole stroke.

Your oppinions and information will be greatly appreciated.

P.S. I'm mostly hoping for a comment from Curtis, our resident diesel expert/fanatic.

[Moppie]

I used to have an old Triumph that would run quite happily at about 500rpm with the ignition turned off.
But it was running very high compression (about 10.?:1), had a very lumpy cam and some very big ugly strombergs on it.
Forunatly it was a manual, or I would have never been able to shut it off, altough on a flat piece of ground it still produced enough power to drive the car forward.
(gotta love old British torque).

However as soon as you gave it some gas, while it was dieseling, it would start to knock almost imediatly, and Im sure would have destroyed itself very quickly if allowed to continue.


Be nice to get the technical reasons behind it, but I believe that petrol when ignited by compression burns to quickly and irraticly to provide a smooth burn at high rpm, resulting in knock, which will destroy an engine very quickly.

[asemstr]

Your kidding right? About turning a gas into a diesal? (Actually I think the original GM diesals were based on modified gas engines, but they sucked!) Before you go to the trouble I'de just get a diesal! As Moppie stated gas engines can run without ignition sys activity because of a condition known as diesalling. Diesalling in gas engines can occur in applications useing a carb and mechanical fuel pump so as long as combustion spontaneously occurs gas continues to flow. The spontaneous combustion is usually the result of hot spots in the combustion chamber igniteing the fuel\air mixture in the chambers. The hot spots can be caused by high heat rated plugs, overheating condition, and carbon deposits (increase comp ratio and retain heat). The hot spots act as combustion initiaters, but efficiency and power output is low compared to precisely timed ignition spark discharge initiated combustion. Now the fuel issue! When it comes to power diesal fuel beats gasoline hands down because it possesses a large quantity of potential energy that when it burns is released in a consistant, controlled manner, while gasoline is known to be more violent and errattic to a point where octane is required to tone it down! Now the base engine in question also needs to pumped up to handle the major increase of stress facters related to attempting to harness the hammering abuse from detonation that can reduce normal gassers to tin foil! I don't see the benefit of your venture, but thats just my opinion!

[beef_bourito]

Thanks for the info, i was wondering precisely that, whether the violent explosion of the gasoline would play a factor. i know that a diesel is alot better, i'm a diesel person myself(i dont own a car but i promote diesel as much as possible). the problem is that people don't know diesels as they are now so if you say a car is diesel they often think that means it's slow and such. I was wondering about other ways to use gasoline that would increase the gas mileage before everyone transfers to diesel.

As for the engine running on knock, i didn't think it would be very possible/feasable because of the stress on the engine and the difficulty involved in getting the fuel to ignite at precisely the right time, it was just a thought.

I think ill try to modify a diesel to run on gasoline anyways, just to see what i get. hopefully it will have better gas mileage and it might be able to be integrated into some cars, it probably wont but you never know. whatever we can do to increase gas mileage is a great thing so don't flame because im thinking outside of the box.

[MagicRat]

Originally Posted by beef_bourito

I think ill try to modify a diesel to run on gasoline anyways, just to see what i get. hopefully it will have better gas mileage and it might be able to be integrated into some cars, it probably wont but you never know. whatever we can do to increase gas mileage is a great thing so don't flame because im thinking outside of the box.

As stated above, the GM diesel car (5.7 liter and 4.3 liter) engines from about 25 years ago were based on gasoline engine designs.

Some racers used the 5.7 (Oldsmobile) engine as a basis for a high performance gas engine. The blocks and cranks were so strong that one could build huge power without breaking it. However, they were also very heavy.

What you suggest is good, in theory. Diesels are more thermodynamically efficient than gas engines due to their higher compression ratio.
However, gasoline will detonate (explode) long before a diesel engine piston will reach TDC, because of this high compression. This means that the engine will not run efficiently, if at all.

Theoretically, one could build a direct-injection gas engine, where the fuel is directly injected into the combustion chamber at the right time.

However, the gas would detonate and not burn. Such detonation is, for gasoline, less efficient than burning it, like in a normal gasoline engine. So power and efficiency will be reduced.

IMO its more efficient to boost a gas engines compression and use a gas with very high anti - knock properties (aviation gasoline), or run the engine on propane, which can tolerate higher compression than any gasoline fuel.

[curtis73]

+1 to all of the above You could make a diesel that ran on gasoline (ingest air and inject fuel as your timing) but gasoline burns so much faster that it would make for questionable reliability. It also burns a bit hotter and may make some exhaust gas temps really hot. Gas engines maintain their exhaust gas temps by burning a stoichiometric mixture, diesels always run leaner than stoich. Might make things hotter than the engine can handle.

I like the theory, but I think what keeps it out of the loop is the heat and the detonation problems associated with the faster-burning gasoline.

[YellowMaranello]

Audi's new 2.0 FSI engine works sort of like a diesel, but not quite. It injects fuel only a few miliseconds before combustion. I had a great link to info on this engine, but I can't find it now. I'll post it up later when I get home.

[asemstr]

While working as a diesal tech I encountered a fair share of driveability concerns related to the "wife" (at least thats who usually got blamed for it! ) filling the tank with 87 octane! A diesal will run on gas, but not very well. Power decreases considerably because of the lower potentiel of power stored in gasoline. This power is also released too abruptly for a shorter period of time so the piston gets a "swat" instead of the push from TDC to BDC provided by the slow consistent exspansion of gasses from burning diesal fuel. Also the octane that gasoline contains is meant to resist spontaneaous detonation from heat so the gas won't burn in the optimum time period, and the burn will be incomplete. So the aforementioned "swat" will come late, get little done, and become a pest ! Then there's the matter of turbo function! Turbochargers are driven by the exspansion of exhaust gasses, so the hotter the exhaust the higher the turbo's output. The weak combustion from gasoline results in lower exhaust temps, and low turbo function further decreasing the engine's power. Then there's the issue of unburned fuel washing down the cylinders causeing excessive wear and reduced compression from the increased ring blow-by, and mixing with the oil in the crankcase lowering its lubricity which can result in engine failure! Another danger of the fuel/oil mix is a runaway engine condition in which the engine starts running on the resulting HC cocktail with no way to shut it down, or stop it from reaching RPMs that will likely end in a big bang! Even in cases where the engine only ran for a short period on gasoline the injecters usually endure huge amounts of wear from the nearly nonexistant lubricity factor of gasoline and lock up! So the my point is..Diesal engine+ Gasoline=Bad news!