Experimental Comparison of Low-Load Piston Compounding Deactivation for the DBDC+EC Engine Architecture

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. This Downsized Boosted Dilute Combustion, Exhaust Compounded (DBDC+EC) engine concept has shown great potential for improvements in efficiency at high loads through extended second expansion process, but suffered from excessive expander cylinder pumping and low exhaust temperatures at low loads. Four expander operating strategies were experimentally tested and simulated at a range of engine speeds and loads to determine the most efficient method to deactivate the piston compounding at low loads. The most effective method involved deactivating all the expander valves and operating it as an air-spring while diverting power cylinder exhaust gasses through a separate bypass port. While this method requires some unique hardware development to enable on-the-fly actuation, it offers 15% to 22% improvements in low-load BSFC over the active expander method while improving exhaust temperatures by 100° to 150°C.