Turbo Compounding of a Naturally Aspirated Single Cylinder Diesel Engine – A Simulation and Experimental Study

Almost one-third of the fuel energy is wasted into the atmosphere via exhaust gas from an internal combustion engine. Despite several advancements in waste heat recovery technology, single-cylinder engines in the market that are currently in production remain naturally aspirated without any waste heat recovery techniques. Turbocharging is one of the best waste heat recovery techniques. However, a standard turbocharger cannot be employed in the single-cylinder engine due to technical challenges such as pulsated flow conditions at the exhaust, phase lag in the intake and exhaust valve opening. Of late, the emphasis on reducing exhaust emissions has been a primary focus for any internal combustion engine manufacturer, with the onset of stricter emission norms. Thus, the engine designer must prioritize emission reduction without compromising engine performance. Current work focuses on enhancing the power output of a 0.6-litre, single-cylinder naturally aspirated diesel engine by employing a power turbine. Since the exhaust flow conditions were pulsated, an impulse turbine was employed. One-dimensional simulation studies were carried out after validating the base naturally aspirated engine model. An impulse turbine was designed and simulated for the pulsated flow conditions. Simulation results show that the single-cylinder naturally aspirated engine delivered a superior performance with turbo compounding. The brake power output of the turbo-compounded engine improved by 6% compared to the base NA version. Also, the thermal efficiency of the turbo-compounded engine improved by 2%. HC emissions were reduced by 31% and CO emissions by 11% for the turbo-compounded engine. Soot emissions were 2% lower, and NOx emissions were 5% lower for the turbo-compounded engine than the base naturally aspirated engine. Thus, turbo-compounding is an effective waste heat recovery system that improves the performance and reduces exhaust pollutants of a single-cylinder naturally aspirated engine.