Heavy-duty engine electric turbocompounding

Abstract

This paper analyses the performance of a heavy-duty engine when integrating a turbocompound system including a low-pressure-ratio turbine. The main feature of the low-pressure-ratio turbine is that of achieving efficiencies greater than 75% at very low pressure ratios (of approximately 1.1). The engine performance is predicted by a one-dimensionanl simulation model of a 10 l heavy-duty engine. An electric turbocompound system with a low-pressure-ratio turbine is fitted downstream of the main turbocharger to extract the exhaust gas energy. This additional energy supplies the electronic units and batteries. A method to scale an existing low-pressure-ratio turbine, designed for a 1.0 l gasoline engine, is defined and the changes in the turbine losses and the blade stresses are discussed. Low-pressure-ratio turbines of different sizes are analysed and compared in order to obtain the greatest benefit. In all cases the sum of the engine power and the turbocompound power is matched to the baseline engine power output. The full-load results show a power output from the low-pressure-ratio turbine of up to 15.8 kW, an improvement in the brake specific fuel consumption of the engine of up to 4% and a reduction in the brake mean effective pressure of up to 5%. The recovered exhaust gas energy is higher than the engine power required to balance the increased back pressure due to the additional component within the exhaust system. The electrical power produced is sufficiently high to replace the alternator.