Seems like they would require a lower compression ratio than diesels to ignite, and the engines would be less complex.
Why can't gasoline engines be compression ignited?
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Evadman
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Because it wouldn't be a gasoline engine. it would be diesel. Gasoline combusts too easily and explodes to redily at the tempeatures involed with compression ignition.
You have heard of engine knock? that is copmpression ignition. It is bad in a gasoline engine.
Fuel must burn evenly, not explode to get the most power from it. In a diesel, that means compression ignition. In a gasoline engine, that means using a spark plug to create an even moving flame front.
You have heard of engine knock? that is copmpression ignition. It is bad in a gasoline engine.
Fuel must burn evenly, not explode to get the most power from it. In a diesel, that means compression ignition. In a gasoline engine, that means using a spark plug to create an even moving flame front.
I think it has to do with the consistency of when & how quickly it burns. A Diesel engine has insanely high compression, something like 25:1. A modern gasoline engine has anywhere from 8.5:1 to 11:1.
I think that you'd need to make the cylinders thicker, heads stronger, etc. I've never been in a car that pre-detonated to my knowledge but from what I understand it doesn't feel normal. Maybe you could do this with a smaller displacement engine in the same size block as a normal spark ignited normal block engine....Hrmmm i dont know
somebody smart please?
somebody smart please?
A diesel engine that ran on gasoline wouldn't be a diesel engine. Plus, if you injected at TDC or a bit earlier you wouldn't have knock, you would have useful work.
So are you saying the gasoline would explode because of the uniform heat?
Evadman
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Not that high. Usually the high teens. The Cummins Diesel has a 17:1 ratio.
Basicly, it would burn too fast, and not be controled at all. It goes boom instead of burning in a controled manor.
It sounds like someone hits the engine with a hammer. Which is actually what is happening. 2 flame fronts colide over the piston, and the resulting shockwave slams into the piston like a hammer. There are many words for this occourance. Pre ignition, Ping, detonation, etc. but it is all the same thign. 2 flame fronts form and colide. it is more than possible to knock a hole into the enter of the piston.
Yes, it would be. Diesel does not refer to the fuel used, it refers to the guy who invented the compression ignited engine, Mr. Diesel.
Zenmervolt
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Then, Evadman, to counteract that, why not inject the fuel AFTER TDC? The high pressures would then be put to use more effectively, because the force has a longer lever arm to work on, right?
If a gas engine is really hot and not good repair, they can and do diesel after you shut the key off. Thats what happening when a car doesn't shut off right away with carburated engines.
Demon-Xanth
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- Feb 15, 2000
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It's also known as "Dieseling" in the case of a carburated engine that sputters after being turned off.
It CAN be done, but the fuel is too volitile to be used well. And in the case of modern diesels, 17:1 is a static ratio, you have to add in a 15PSI turbo.
It CAN be done, but the fuel is too volitile to be used well. And in the case of modern diesels, 17:1 is a static ratio, you have to add in a 15PSI turbo.
Originally posted by: geno
can you elaborate? I'm not sure what you're tryin to say there
i think he means usually a diesel engine is accompanied by a turbo, which increases the effective compression of air. the 17:1 ratio is that in the engine cylinders itself, but don't forget that air is being compressed by the turbo at the same time and is then fed into the chamber.
Evadman
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a 15 PSI turbo is actualy doubling the amount of air the engine can take if NA. (14.7 psi at sea level + 15psi)Originally posted by: geno
can you elaborate? I'm not sure what you're tryin to say there
So the perceieved CR is closer to 34:1 because there is 2x the NA amount of air in the Cyl. 30+ PSI is not out of the question. an off the shelf kit from Banks will up the PSI to 34.
When this is done, the engine can actualy last LONGER because the extra air has a cooling effect, so the EGT's are lower. Unlike a gas engine, it is impossible to run a diesel too lean.
This is why some people have been experementing running nitrous on diesels.
Propane?Originally posted by: Evadman
a 15 PSI turbo is actualy doubling the amount of air the engine can take if NA. (14.7 psi at sea level + 15psi)Originally posted by: geno
can you elaborate? I'm not sure what you're tryin to say there
So the perceieved CR is closer to 34:1 because there is 2x the NA amount of air in the Cyl. 30+ PSI is not out of the question. an off the shelf kit from Banks will up the PSI to 24.
When this is done, the engine can actualy last LONGER because the extra air has a cooling effect, so the EGT's are lower. Unlike a gas engine, it is impossible to run a diesel too lean.
This is why some people have been experementing running nitrous on diesels.
The intake charge would have cooled down a bit, plus the pressure would be lower because of the increased volume. What is it, exactly, do you mean by "not controlled"?
Evadman
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Propane addition acts as a catalist to burn more of the diesel fuel. little power is gained from the actual burning of the propane. It is used in very minute amounts.
Please see my first post. I don't know I can make it any easier to understand. *shrug*
1. Gasoline is deliberately formulated to not ignite with compression.
2. Diesel is formulated to have low volatility and easily ignite upon compression.
Diesel have lower auto-ignition temperature than gasoline, but takes more joules per molecule to initiate the chemical reaction. If you filled a diesel engine with gasoline, it won't run, because while compression won't bring gasoline up to auto-ignition temperature.
2. Diesel is formulated to have low volatility and easily ignite upon compression.
Diesel have lower auto-ignition temperature than gasoline, but takes more joules per molecule to initiate the chemical reaction. If you filled a diesel engine with gasoline, it won't run, because while compression won't bring gasoline up to auto-ignition temperature.
It is difficult to explain without a lengthy post, but gasoline is too volotile and burns too quickly to make an efficient diesel. If you have the balls, you can put out a match in a can of diesel, try doing that with gasoline...boooom.
This is also the reason that you cannot have a high RPM diesel engine, the diesel does not burn fast enough to keep up with the speed of the engine. Easy to make big torque on a diesel, not so easy to make big HP.
This is also the reason that you cannot have a high RPM diesel engine, the diesel does not burn fast enough to keep up with the speed of the engine. Easy to make big torque on a diesel, not so easy to make big HP.
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