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Originally Posted by sperry
Fuel does not provide the power in a combustion engine, oxygen does. The fuel is just a catalyst to make the oxygen burn more easily.
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This is not correct.
Fuel does provide the majority of the energy in combustion, that is why it is called fuel. Fuel is also not a catalyst as it is consumed in the reaction. Catalysts aid in a chemical reaction, but do not get changed as part of the reaction
Oxygen does not burn. If it did, lighting a match would cause the atmosphere to explode! Oxygen is an oxidizer, as is hydrogen peroxide, and most anything that ends in "ites", or "ates". Technically, oxidizers don't even have to have oxygen, just the ability to accept electrons. Halogens such as chlorine, bromine, etc are also oxidizing agents.
Combustion (the combining of fuel and oxidizer) produces energy in the form of heat, water(for oxygen based oxidizers), and byproducts (whatever is left of the fuel that did not combine with oxygen)
Under normal engine conditions, the flame initiated by the spark progresses across the chamber in a "controlled" fashion producing heat and pressure the later of which moves the piston. Detonation is "uncontrolled" combustion that is effectively multiple flame fronts crashing into each other at very high speed. That crashing is the sound you hear as a knock, or ping. The extreme heat and pressure associated with detonation can literally blow up your engine either over time, or possibly even all at once.
There is an optimal fuel/oxidizer mixture that produces the maximum energy without detonation. With modern combustion chambers and fuel, the optimal ratio is around 13:1, but most cars run around 14:1 which generates fewer emissions.
So if you add a little more air, you car may get closer to 13:1.
The problem is that if you go to far, (lean), detonation becomes more likely due to the increased heat and pressure.
There is a ton more we could talk about detonation, and A/F mixtures, but that is enough for now.