[revetec]

Originally Posted by hightower99

Yes that is right. But i would say that it is easier to notice knocking at low RPM and that you absolutely wouldn't want it to occur at high RPM (where you might have 5-10 heavy knocks happen before you can react and let up). My point was that the reason that engines run open-loop rich at WOT is to protect against knock (at all speeds).

To some degree you are correct. Basically a fuel map is set up to provide a mixture that is lean enough to provide the best performance while providing a level of emissions to an acceptable point. Compression ratio, fuel rating, combustion chamber design, fuel system, fuel mixture, ignition map, engine and combustion chamber temperature etc. all play a part in this scenario. Some engines are more prone to detonate due to their design, and also carbon build up is also a factor. A lower compression engine will not be as prone to detonation as a higher compression engine as well.

Maybe sweeping statements from either you or myself on this point will not be 100% correct, due to the amount of variables in this argument.

There is no doubt that a richer mixture will aid in reducing detonation, but also a higher octane fuel will also do the same thing. Get my point?

Basically you tune an engine to the highest performance with a reasonable level of emissions. Included in this process is not allowing the engine to detonate. A slightly leaner mixture than 14.7:1 usually gives the best power result, but a consideration has to be made to Nox as a leaner mixture usually produces higher Nox. Funny thing is that our engine produced less Nox at a leaner mixture, but this is probably a combustion chamber design issue.

Then the closed loop parameters are set to provide an air/fuel ratio that allows the Catalytic Converter to operate properly.

I suppose we were both looking at this the wrong way around. Open loop is usually the optimal power Vs emissions program, while closed loop is a fine tuning for the Cat and the lowest emissions, (instead of the argument that closed loop is the set mixture and a richer mixture in "Open Loop" is used to reduce detonation?) Correct?