DESIGN AND DEVELOPMENT OF A LOW PRESSURE TURBINE FOR TURBOCOMPOUNDING APPLICATIONS

Abstract

This paper describes the development of a high performance low pressure turbine (LPT) for turbocompounding applications to be used in a 1.0 litre ”cost-effective, ultra-efficient gasoline engine for a small and large segment passenger car”. Under this assumption, a mixed-flow turbine was designed to recover latent energy of discharged exhaust gases at low pressure ratios (1.05 - 1.3) and to drive a small electric generator with a maximum power output of 1.0 kW. The design operating conditions were fixed at 50,000 rpm with a pressure ratio of 1.1. Commercially available turbines are not suitable for this purpose due to the very low efficiencies experienced when operating in these pressure ratio ranges. The low pressure turbine performance was simulated using a commercial CFD software. Then, turbine performance was validated with a comprehensive turbine testing that was accomplished by using the Imperial College turbine test rig. The testing and the simulation conditions were conducted for a range of design equivalent speeds spanning between 80% and 120% at steps of 10% increase. In addition, the impact of the turbocompounding on Brake Specific Fuel Consumption (BSFC) and Brake Mean Effective Pressure (BMEP) was also assessed by using a 1-D validated engine model of the engine under study. Three different arrangements for the turbocompounding were assessed: (1) precatalyst, (2) post-catalyst and (3) in the wastegate of the main turbocharger. The outcomes of the simulation were compared to those obtained for the baseline engine and are discussed in the the paper. The 1-D engine simulation had shown that the maximum benefit of the turbocompounding can be achieved when it was located at the post catalyst with maximum BSFC reduction of 2.4% at 1500 rpm and 3.0% of BMEP increase at 1000rpm.