OK, I might be asking a big dummy question here - so I'll stand back as the responses come in.

Would it be possible to have a high compression gasoline engine with no spark plugs? If diesel is heavier and can ignite under high pressure, why not spark plug free gas engines? Am I missing a fundamental principle of engine building?

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Barker

I believe that I read recently that such compression ignition gasoline engines are being developed and that they are more efficient than the spark plug type. I think it is a consortium that is working on it.

DS
87 300D

found an article:
japanese study

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Barker

I've seen these quite a few times before. Usually way out of tune pieces of junk that continue to diesel (run) after being shut off.

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85 300CD
83 300TD
78 240D (daughter)

The problem is preignition, by and large. If the compression is high enough for good autoignition, the mixture will inevetibly burn before TDC. Diesels don't have this problem because the fuel is injected at the correct time for proper combustion. A side note, if you use propane "fumigation" you can get this problem if you use too much and the mixture is actually ignitable during compression. Usually blows the head off.

Don't mistake this for direct injection, used by Benz on some early injected engines in a directy "ripoff" of the Daimler "upside down" V12 aircraft engine. In that case, fuel is injected directly into the combustion chamber just like a diesel, but earlier and there is still a spark plug to initiate combustion. Very powerful, but prone to severe carbon buildup and "reverse" effects from excessive pressure on the pintles in the injectors (that is, combustion gasses in the injectors). Benz and Bosch solved that problem on the direct injection engines by putting the injector in the block aimed upwards, so that the piston covered it during ignition.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!