Study of Parallel Turbocompounding for Small Displacement Engines

In order to reduce greenhouse gases and respect stringent pollutant emission regulations, the modern engine is increasingly required to incorporate energy recovery systems to enhance performance and increase efficiency. This paper deals with the exhaust energy recovery through turbocompounding. Both series and parallel turbocompounds are discussed. In the first part of the document, literature on turbocompounding is introduced. Then a simulation study carried on AMESim software, using a 2L Diesel engine model is presented. The parallel turbocompounding is simulated by expanding a part of the exhaust gases in a converging nozzle instead of the turbocharger turbine. The power produced is evaluated as a function of the pressure drop in case a turbine is mounted instead of the nozzle. A global study over the entire engine map is described, and two steady state points 2000 rpm, 8 bar and 3500 rpm, 7 bar are chosen. The former is from the NEDC cycle and the latter represents an extra-urban running. To analyze the impact of the system on the engine performance, both the original and turbocompounded engines are compared, by maintaining constant the mass of fuel injected during the engine cycle. While the main effect of the series architecture is the back pressure, the parallel one has an effect on boosting since the mass flow rate crossing the main turbine is reduced and so the power driving the compressor. The potential of this system is evaluated on the basis of the power recovered by the system and lost in the engine due to its negative effects.