Kinetic study of electron transport behaviors used for ion sensing technology in air/ EGR diluted methane flames

Abstract The real-time detection of the key combustion status such as combustion timing, misfire and knocking will be crucial for the future internal combustion engines. Ion sensing technology can be potentially applied to develop the ion current based combustion detecting sensor on mass-produced engines. However, the low signal to noise ratio (SNR) of the ion current signal still be a major obstacle for the large-scale application of this technology, especially when the lean mixtures or exhaust gas recirculation (EGR) is applied on the engines. In order to improve the SNR, a fundamental study on the ion current formatting process in air/EGR diluted methane flames in studied in this paper. A kinetics analysis of the electron transport behaviors in the electric field is conducted. By solving the Boltzmann’s equation, the electron transporting parameters can be predicted. The in-flame electron motion predicted through this method is more accurate than through the model based on thermal equilibrium assumption, especially when an external electric field is applied. Besides, a multi-physics CFD model of the methane flame coupling electrohydrodynamic of the flame plasma is established. Combined the numerical results and the experimental results achieved in a constant volume combustion chamber, the electron–ion diffusion process and their distributions with different diluting conditions is investigated. Consequently, the characteristics of the ion current signals in the excess air/ EGR diluted methane flames can be well predicted. A further improvement of the ion sensing technology could be achieved based on the above analyzing results.