High Speed Endoscope Imaging to Supplement CFD Analysis and Combustion Testing for SIDI Engine Startup Development

Optimization of engine startup from crank to catalyst light-off is essential for achieving low emissions. For Spark Ignition Direct Injected (SIDI) engines, this requires optimization of the piston crown features, spray characteristics and control strategy. In this case study, high speed endoscope imaging was used to provide a qualitative confirmation of CFD spray predictions and to provide insight into engine starting in a “real” engine environment. The effect of piston feature was initially evaluated in a single cylinder engine running the dual-injection catalyst heating mode. The piston features were also assessed at part load and wide open throttle. The videos of the spray development were compared to CFD predictions. In the example case reported here, endoscope imaging showed that the baseline piston bowl was not effective in deflecting the spray toward the spark plug. Moving the piston bowl toward the injector gave a visible improvement in the spray deflection. Engine tests confirmed improved combustion stability. A unique rigid camera-mounting system allowed similar endoscope access on a multi-cylinder engine to provide continuous imaging of the actual crank, crank-to-run, and light-off processes. The impact of injection pressure during startup on the initial spray and combustion events could be readily visualized to assist calibration. These results confirmed that high speed endoscopy can be applied to practical engine development programs for qualitative CFD validation and to assist in engine startup and catalyst heating mode development.