Explore and Extend the Effectiveness of Turbo-Compounding in a 2.0 Litres Gasoline Engine (Second Report: Fuel Economy under Part Load Condition, Transient Performance and Effect of Pressure Ratio)

The turbo-compounding has been extensively researched as a mean of improving the overall thermal efficiency of the internal combustion engine. Many of the studies aiming to optimize the turbo-compounding system lead to the unified conclusion that this approach is more suitable for the operation under constant high load condition, while it has little effect on improving the fuel economy under low load conditions. Besides, in a traditional series turbo-compounding engine, the increased back pressure unavoidably results in a serious parasitic load to the system by increasing the resistance to the scavenging process. In order to improve this situation, a novel turbo-compounding arrangement has been proposed, in which the turbocharger was replaced by a continuously variable transmission (CVT) coupled supercharger (CVT superchargedr) to supply sufficient air mass flow rate to the engine at lower engine speeds. The exhaust was directed to the power turbine that converted the waste heat into useful mechanical work and fed it to the crankshaft. According to the results, the CVT superchargedr helped to increase the brake torque by up to 24% (compared with a turbocharged counterpart) at 1500 revs/min. In the exhaust end, the power turbine increased the brake torque by 7% at the engine speed of 3000 revs/min and above. The brake specific fuel consumption (BSFC) was reduced by up to 8% at rated engine speed.

In this report, the performance of this system will be further explored considering the fuel consumption under part load condition as well as the transient performance. The CVT drive ratio and thus the pressure ratio of the compressor will be further optimized to achieve the best fuel economy and drivability. Similar with the previous paper, the system model in this paper was also built in GT-Power which is a 1 dimension (1-D) engine simulation code.