Combustion timing in HCCI engines determined by ion-sensor: Experimental and kinetic modeling

The ion current signal in homogenous charge compression ignition (HCCI) engines is studied to show that a measurable ion current exists even in the very lean combustion in an HCCI engine. An ion sensor signal is observed in a propane-fueled HCCI engine, which can be used in place of the expensive pressure transducers currently used in research engines. The ion sensor is equally capable of capturing cycle-to-cycle variations in HCCI combustion. A numerical model using detailed chemistry was developed for HCCI combustion and used to predict the ion concentration in the cylinder. The model results agree with experimental findings. The ion signal becomes stronger with increases in equivalence ratio and intake temperature. Due to the low temperature and high pressure HCCI combustion, the N₂O mechanism contributes significantly to the total NO_x production. In some cases, the N₂O route produces more NO_x than the Zeldovich route. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).