Turbocharger Turbine for Charging a Lean-Burn Gasoline Engine
2022-01-0452
03/29/2022
- Event
- Content
- Lean-burn combustion is a promising technology for reducing fuel consumption and CO2-emissions of gasoline engines. Due to the air dilution, the indicated engine efficiency increases, resulting in lower fuel consumption and less CO2-emissions. However, the air dilution decreases the combustion temperature, which leads to increased demands on the charging system. In order to map the same engine operating point, higher boost pressures are required at lower available exhaust enthalpy. This places high efficiency requirements on the turbocharger. Hence, state of the art single-stage turbochargers are unable to provide enough boost pressure to enable lean-burn over a sufficiently wide engine operating range. In this paper, a single-stage turbocharger turbine is developed with the objective of enabling a lean-burn engine operation with an air-fuel ratio of λ=2 in the range of the Worldwide Harmonized Light-Duty Vehicles Test Cycle (WLTC). For this purpose, extensive 1D-engine simulations are performed with the baseline compressor and a simple turbine model. The results show that a turbine efficiency of more than 70% over a broad operating range is required for the desired engine operation – especially with regard to the low-end torque. Based on the crank-angle-resolved engine simulation data, turbine requirements are determined. Their evaluation shows that an axial turbine is favorable compared to conventional radial turbines. Next, a preliminary axial turbine design is carried out using 1-D/2-D design approaches. Then, the corresponding performance map is calculated by 3-D CFD simulations showing isentropic total-to-static turbine efficiencies of up to 77% over a wide operating range. Ultimately, the derived turbine performance map is implemented into the 1D-engine model replacing the simplified turbine object. New simulation-results show a significantly extended λ=2 operating range and promising benefits in brake-specific fuel consumption compared to the baseline turbine.
- Citation
- Sagan, L., Kuestner, C., Eilts, P., and Seume, J., "Turbocharger Turbine for Charging a Lean-Burn Gasoline Engine," SAE Technical Paper 2022-01-0452, 2022, .