Multi fidelity study of the performance characteristics of a five-stroke engine

This work presents a multi-fidelity investigation of a five-stroke engine, using 0D air standard model, 0D two-zone combustion model, and 3D turbulent combustion CFD models. Compared to prior 0D/1D work, this study explores the differences in the results of different simulation models while also identifying significant performance limiting parameters. Results are reported as indicated thermal efficiency over a range of design characteristics, including overall expansion ratio, clearance volumes, and valve timing events. Pressure–volume relationships, work output, mass and heat transfer are also examined to investigate simulation model performance and areas for improvement. It was found that the low-pressure cylinder clearance volume ratio, and the pumping work during the exhaust stroke have significant effects on the engine’s performance. The pumping losses are found to increase with the overall expansion ratio limiting the usable overall expansion ratio and achievable efficiency. Additionally, incremental increases in exhaust valve time-area do not significantly reduce exhaust pumping work, suggesting that a more radical approach is required. 3D CFD provides improved simulation accuracy over prior 0D models, which are unable to accurately capture the gas flow processes.