Ugo, yes, I know what you are saying. I have done much research. I know I'm dealing with HCCI engines and the limitations. That is exactly the point I'm trying to make. Random guessing a fuel for an uncommon unknown engine design is probably not going to yield a superb engine. All of the research done with HCCI is pointing to complex systems involving exhaust gas recirculation by variuous means, inlet temperature control, and complex engine monitoring systems to predict HCCI combustion. And you are right, the best fuel for this type of engine is unknown. I just don't think this type of engine will be possible at the model level without any sort of auxiliary systems at all.

From the modeling aspect we started with fuel containing kerosene. The research shows that kerosene or diesel fuel is acceptable for combustion. I know it works in my engines. But it will not approach lambda ratios of 1 or greater. These small engine just won't run. I think the problem is vaporization. That is where I'm going to put my efforts for now.

I have no way of measuring in cylinder temperatures or pressures. I wish I did. I think pressure sensors will be easy to add. I don't know much about this sort of temperature sensor. I have a flow meter that I will use to measure the air consumed by the engine to get a better idea of air/fuel ratios. So far the little engines run very rich. Even D-Star's engines with the tiny bit of information I found run rich, but do make a good amount of power for the displacement.