Ignition Diagnostics in EGR- and Air-diluted Methane/Air Mixtures Using Spark Induced Breakdown Spectroscopy

A diagnostic tool based on Spark Induced Breakdown Spectroscopy (SIBS), designed and developed for providing information on the mixture composition at the spark plug location, was successfully used in diluted methane/air mixtures at engine relevant conditions. The INSIDE technique (INduced Spectroscopy for Ignition Diagnostics in Engines) allows deriving information on the local fuel to air equivalence ratio (?) in the vicinity of the spark plug and on operating pressure based on the features of the spectral emissions. In the present work, a capacitive discharge ignition (CDI) system is used for the first time for SIBS-based ignition diagnostics in spark-ignition engines? relevant conditions. The mixture dilution is performed following different approaches: dilution with synthetic EGR, dilution with pure nitrogen, and dilution through ? variation with and without constant EGR addition. Spectral signatures are measured in the spark plug location, and the peaks intensities of four atomic lines (hydrogen at 656?nm, nitrogen at 744?746?nm, carbon at 765?769?nm and oxygen at 777?nm) are compared to the non-diluted stoichiometric mixture. The atomic peak intensity ratios show distinct trends depending on the dilution strategy selected. Therefore, the atomic line ratios can be used to extract information on the local mixture composition also in the case of EGR dilution.