Is Oxygen All That Engines Need Atmospheric Air For?

Hi,

So I was just going through the air density part of efi tuning fundamentals and it was mentioned that oxygen was the only thing that we are really interested in, which makes sense when making calculations for tuning purposes. However, I was told that it is actually the nitrogen, which is inert, that actually does the expanding to create cylinder pressure as a result of being heated by the burning of the oxygen and the fuel. I am basically just wondering if this is true or not.

Your understanding is correct but, remember, they are two different things.

The engine works by the heating of the gases in the combustion chamber, by burning the fuel, and using the resulting pressure increase to push down on the piston. As such the nitrogen, and other trace gases in the air are an important part of this expansion and/or pressure increase, the resulting CO2 and H2O (as steam) play the other part as they are also gases formed from the burning fuel and oxygen.

For EFI tuning considerations, the nitrogen, etc, isn't really a concern because we only want to know how much oxygen is entering the cylinder, so we can supply the correct amount of fuel (for the desired lambda).

I hope that helps.

That is very helpful. I actually hadn't considered the CO2 and H2O and am glad you pointed that out. Thanks for your time and knowledge.