Spark plug-based diagnostics for fuel-air ratio determination

Experiments were performed in a simulated combustion chamber with non-combustible and combustible mixtures to study the feasibility of spark plug based diagnostics for fuel-air ratio determination in the spark plug gap of a Spark Ignition (SI) engine at ignition. During the experiments, the breakdown voltage (V{dollar}rmsb{lcub}s{rcub}{dollar}) as well as the spark light emission were measured to correlate to the characteristics of the gas mixture. A simulated combustion chamber was used rather than an actual engine to obtain better control of mixture composition and other experimental parameters.; The dependence of V{dollar}rmsb{lcub}s{rcub}{dollar} on the pressure, the temperature, the gas composition and the gap size was tested in non-combustible mixtures by measuring the true values of V{dollar}rmsb{lcub}s{rcub}{dollar} and the agreement between the experimental results and Paschen's Law was studied. In addition, the correlation between V{dollar}rmsb{lcub}s{rcub}{dollar} and the fuel-air equivalence ratio ({dollar}phi{dollar}), as well as the residual gas fraction (RGF) was tested in combustible mixtures.; In the measurements of spark light intensities, relative intensity (the spectral intensity of a particular molecule normalized by the shot or broadband intensity) was studied to reduce the effect of the variations of orientation of the spark initiation. The relative intensity of the CN radical, centered at 385 nm, was tested to have the strongest intensity 5 {dollar}mu{dollar}s after the spark ignition compared to those of the other radicals, such as CH and NH. It has also been found that the relative intensity of CN has great dependence on {dollar}phi{dollar} as well as RGF.; The study of this spark plug based diagnostics provides a feasible method for determination of mixture composition in the spark plug gap at ignition.