Investigation of Combustion Robustness in Catalyst Heating Operation on a Spray Guided DISI Engine, Part 1 - Measurements of Spark Parameters and Combustion

In the catalyst heating operation for a spray guided DISI (Direct Injection Spark Ignition) engine, split injection has been shown to improve combustion stability which is critical for the trade-off between tailpipe emissions and vehicle idle NVH [ 1 ]. The spray guided DISI engine has a multi-hole injector centrally located in the chamber with the spark plug. For catalyst heating operation, the first injection occurs during induction, which forms a relatively well mixed but lean mixture in the cylinder before ignition, and the second injection occurs close to a retarded ignition, which produces a stratified fuel rich mixture in the central region of the combustion chamber.

Combustion initialization is found to be sensitive to spark plug protrusion and orientation, injector orientation and 2 ^nd injection timing relative to ignition [ 1 ]. High Tension (HT) measurements of current and voltage have been taken to characterize ignition, and show how arc parameters can be related to the subsequent combustion performance. The breakdown voltage and current have been measured with sample-hold circuits since the arc parameters were only recorded at 300 kHz. Bench tests with and without flow (and with liquid fuel on the earth electrode) have been used to elucidate the effect of spark plug geometry and orientation. High speed videos of the spark have been combined with the arc voltage and current histories. The results show how flow and the presence of fuel modify the arc, and the engine tests show how incorrect phasing of the second injection can induce misfires.