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Name: Tony
Status: Student
Grade: 9-12
Location: FL
Country: United States
Date: August 2006


Question:
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?



Replies:
Hi Tony,

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 at once.

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!

Regards,

Bob Wilson


Tony,

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.

Ryan Belscamper



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