Downsized Boosted Dilute Combustion, Exhaust Compounded (DBDC+EC) Experimental Engine Design, Thermodynamic Model Comparison, and Performance Potential Predictions

An experimental piston compounded engine was designed with guidance from thermodynamic modeling, then was built and tested to compare the model predictions to measured results. The piston-compounded concept has shown great potential for improvements in efficiency over current state-of-the-art light-duty engines through the use of an efficient second expansion process to more fully recover energy still present in the exhaust gasses, and was further developed into the Downsized Boosted Dilute Combustion, Exhaust Compounded (DBDC+EC) engine presented here. This paper documents some of the more unique design elements of this engine as well as a performance comparison between test data and modeling expectations. Ultimately, an experimental stoichiometric spark-ignited piston compounded engine was designed, five blocks were built, and collectively they were run for thousands of hours. The experimental engines achieved a minimum of 222 g/kW-hr BSFC with a wide region of operation under 250 g/kW-hr, and the performance matched predictions from a thermodynamic model that reflected the as-built hardware. Predictions for a 2nd generation DBDC+EC engine result in a 10% fuel economy improvement over a similar downsized boosted stoichiometric SI engine, with an additional 9% improvement for lean operation at low load. These result in minimum BSFCs of 212 and 206 g/kW-hr for the stoichiometric and lean DBD+EC Gen 2 engines respectively.