A Comparison of Combustion Temperature Models for Ionization Current Modeling in an SI Engine

Combustion temperature models for spark ignited engines are investigated in this work. The temperature models are evaluated as sub-models of a model for the thermal part of ionization current.

Three different combustion temperature models were investigated; a single-zone model, a mixed two-zone model and an unmixed two-zone called a kernel-zone model. The combustion temperature is derived from cylinder pressure. The ionization current model structure also contain sub-models for formation of nitric oxide (NO) and its thermal ionization. The model output is compared to the measured ionization currents with respect to peak amplitude and position.

Also, two models for NO formation are evaluated. The first is a fixed NO molar fraction model and the second is a reaction rate controlled NO formation model based on the extended Zeldovich reaction scheme.

It is shown that a kernel-zone model shows better performance in both peak amplitude and peak position than both the single-zone model and the mixed two-zone model. Both NO formation models showed equal performance for high temperature combustion but the rate controlled NO model can make an important contribution in cases with lower combustion temperatures.