Steve, thanks for the insult.

I do understand the difference between a diesel cycle and a spark ignited
engine. While my thermodynamics classes were decades ago we did study the
matter.

I am sure that gasoline would also self-ignite quite well during a diesel
cycle. Maybe the compression ratio would have to be reduced thereby also
reducing stress on the engine parts.

Try me with your longer answer and see if I can comprehend.

Ivan Vegvary


What you are questioning involves two different petroleum distillate
products with entirely different properties. These properties are differing
densities, differing lower flammability levels, differing lower explosive
levels, different specific densities, and countless differences in
lubricating properties. The engines designed to burn these products are
designed metallurgically and mechanically to take advantage of the
properties of each fuel and to be able to handle their consumption through a
controlled explosion. While it is true that diesel engines can be started
with gasoline in some engines specifically designed to do so, the extra
design components are not present in the common engines of either variety.

One engine uses simple compression pressure to ignite the fuel (diesel) and
an impulse spray (or two sprays in some newer models) at the precise moment,
while the other one utilizes a spark at a precise moment that is calibrated
by the timing gears and connector, be they a chain, or common gears. The
fuel delivery systems vary considerably, even in the gasoline engines, with
common aspiration by suction through a carburetor to computer controlled
fuel injection being the common types. Carburetors may be either updraft or
downdraft. And then, the fuel mixtures may be given an additional boost in
pressure by a turbocharger powered by exhaust gases or a supercharger
powered by a mechanical connector ultimately ending up at the crankshaft but
possibly running through intermittent components. Superchargers are and
were commonly used for diesel engines, and fathered drag racing's
development through the 4-71. 6-71, and the grand daddy 8-71 superchargers
of the early engines, commonly called "blowers". They are still in use,
although the new ones are a few light years ahead of surplus superchargers
the early drag racers used.

The compression ratio on a diesel engine is higher than a gasoline engine.
This is a rating of XX:1 to rate how high a pressure is created by the
upstroke of the piston when compressing the fuel/air mixture when the piston
reaches top dead center, and full compression is achieved. Gasoline has
properties that cause it to ignite when exposed to sudden bursts of
pressure, and cannot be as predictably controlled as diesel fuel.
Therefore, if gasoline is run with high pressure as an ignition source,
detonation occurs before the piston has reached top dead center, much like
any gasoline engine, yet detonation occurs so far before the three or four
degrees before top dead center of the piston travel that the preignition
knock can cause damage to the piston, cylinder walls, rings, connecting rod,
connecting rod pins, or all the above. This has been a problem with
gasoline engines for decades, particularly when engines used a points system
on the distributors with a vacuum driven mechanical advance to adjust the
spark according to driving conditions and how much you pressed the gas
pedal. Preignition knock was the cause of catastrophic failure for an
untold number of gasoline engines, particularly in the era of the transition
from leaded to unleaded gasolines, and all the additives and fuel
concoctions and devices to help the public (and in some cases to merely
relieve them of cash) didn't really work very well.

If gasoline were to be able to be run in a diesel engine, even with the
addition of spark plugs, the operating temperatures would surely also cause
erosion of metal due to excessive pressures, and the piston rings would soon
lose their seal, making the engine stop running.. Excessive temperature may
cause melting of the components or simple seizure of the piston in the
cylinder. Your sureness that gas would run in a diesel engine is flawed.

Differences between gas and diesel engines are many. Fuel flow, fuel
delivery, piston rings, compression ratios, metallurgy, sulfur vs.
non-sulfur fuel, gas/ethanol mixes vs. diesel fuels, properties that could
cause detonation of gasoline in diesel injector systems before the fuel even
reaches the injector nozzle, vast differences between the explosive
volatility of diesel fumes and gasoline fumes, exhaust systems combined with
emissions controls devices, changing fuels and the effect of that on
anti-pollution devices sensors and systems, catalytic converters, computer
controlled sensors valves and gates that would be pushed outside their
operational parameters with the introduction of a foreign fuel that the
system was never intended or designed to burn ........ it goes on.

Diesel fuel in a gasoline engine would not work because the compression
ratio (remember that, we touched lightly on that in another paragraph) is
not high enough to make the diesel fuel ignite, and either with a fuel
injection system, or a carburetor, it just wouldn't work, or work for very
long even with the spark plug firing. If it DID fire and run, it would not
do so for very long before spark plug fouling. Sorry I can't give you a
longer answer than that.

I may be wrong on some of the small points, and I'm sure that people here
who know far more than I do will pick apart my mistakes. This is only a
feeble attempt to explain what you requested, and no claim of perfection is
made or implied.

But I do know my ass from a hole in the ground and not to put diesel in a
gas engine, or vice versa.

Hope this is a long enough answer. If not, go to Google. After that, if
you're still wondering, dazed, and confused, just go try it and report back
on how it goes.

Steve