Optimization of a Wastegate Turbocharged Medium Speed Diesel Engine

An eleven litre four stroke medium speed marine diesel engine has been studied with different wastegate turbocharging systems to improve low speed/part load engine performance.

A previous Glasgow College model was adapted to simulate the engine operation under steady conditions. A variation to the Single Zone Fuel Model developed by Watson, Pilley and Marzouk was proposed and a Schwitzer-type wastegate turbocharger model was developed.

A series of exhaust wastegate turbochargers have been simulated and tested to identify matching of the various turbomachinery configurations and the effects of these on engine performance. Both simulation and experimental results show that the wastegate bypass system can be modified to advantage by proper selection of the wastegate discharge flow mixing point along the engine exhaust system. The best low speed engine performance was obtained with the wastegate discharge flow exhausting directly to the atmosphere. The worst performance was obtained with the conventional mixing method, where the wastegate bypass flow is mixed with the turbine discharge flow inside the turbine housing. Considering the application feasibility, a compromised wastegate system is recommended with wastegate and turbine exhaust mixed downstream near to the exhaust elbow.