In-Cylinder Equivalence Ratio Measurements in an EGR Equipped Engine

A single-cylinder natural gas fueled engine equipped with an exhaust gas recirculation (EGR) system was ignited using a laser. The broadband emission from the spark kernel was spectrally resolved, and the peaks corresponding to $Hα$⁠, N, and O atoms were measured for a range of conditions with global equivalence ratios ranging between 0.6 and 1.0 and for exhaust gas recirculation fractions up to 29%. The $(Hα/O)$ and $(Hα/N)$ peak intensity ratios from the spectral scans correlated extremely well $(R2>0.97)$ with local oxygen based equivalence ratios. Appropriate relations were developed to relate such values to global equivalence ratios and the EGR rate. For a homogeneous intake charge, the present laser induced breakdown spectroscopy diagnostic enables an estimation of one of the two values, global equivalence ratio or EGR rate, with the knowledge of the other.