Oxygen in Engines
Country: United States
Date: August 2006
I have read about the proposed use of pure oxygen
(or controlled amounts of it) in spark-ignition engines. As I
understand, many flammable materials becomes several times more
combustible in a pure oxygen environment. Gasoline could probably
detonate and only slightly elevated temperatures and pressures,
making it mostly useless in a spark ignition engine.
However, in a compression ignition engine, where such explosive
detonation in normal, wouldn't pure, or above normal oxygen levels
increase performance and efficiency (if for example a belt driven
oxygen distiller was installed in a diesel) by allowing more fuel to be
burned per engine size and by allowing more efficient and clean
combustion of fuel?
Replacing the air used in any internal combustion engine with
oxygen, is more or less the same thing as supercharging it.
The use of oxygen requires additional fuel to burn with it,
resulting in greater cylinder pressures and greater power.
A spark ignition engine works perfectly well with the use of
pure oxygen. A typical post WWII torpedo consisted of a small
V8 motor, a large tank of pure, very high pressure oxygen and
a small tank of gasoline or similar fuel. The motor ran on
pure oxygen and the above fuel, and produced an extremely
high specific power output.
The octane rating of gasoline is essentially unchanged by
burning it with pure oxygen, although the greater rise in
cylinder pressure during combustion (as a result of more fuel
being burned in the same enclosed space), may require the use
of higher octane fuel.
Explosive detonation is definitely not normal in any engine,
whether spark ignition or diesel, and in fact is destructive
to either type of engine. In the case of a diesel, explosive
detonation is essentially impossible, since the fuel burns
progressively as it is injected, and thus cannot explode all
One advantage of burning pure oxygen, would be the
elimination of NOx (nitrogen oxides) emissions, since even
though the higher combustion temperatures would normally
result in dramatically increased NOx, there is no nitrogen
drawn into the motor to react with oxygen to produce any NOx.
As for the use of a "belt-driven oxygen distiller", I know of
no such device. The closest thing to it is a pressure-swing
oxygen concentrator, but such a device would have to be
extremely large to be able to supply the needs of an engine
in real time, and in any event it only increases the oxygen
concentration; it does not produce pure oxygen. Pure oxygen
is generally produced by the fractional distillation of
liquid air, and liquid air is produced by cryogenic
refrigeration... not the sort of thing you want under the
hood of a car!
While I am not aware of what the 'ideal' oxygen content would be,
there is advantage to having other gasses present in the engine.
An internal combustion engine is a heat engine, it relies on the
heat of its burning fuel to produce an effect. That effect is to
heat the (already) compressed air in the piston, causing an increase
in its pressure. This pressure is transferred through the piston
and crankshaft to be the power you think of an engine
producing. Using a pure oxygen injection system would minimize the
amount of gas being heated in the chamber.
On the other hand, acquiring and carrying around sufficient pure
oxygen to fuel a typical motor vehicle would probably be more effort
and be more impractical than the over all gain in efficiency could
justify in the first place.
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Update: June 2012