Parametric Study on Electric Turbocharging for Passenger Cars

The motor generator unit installed on the turbocharger shaft (MGU-H) provides a fundamental contribution to the amazing performances and efficiency of the last Formula 1 power units. The excess of exhaust gas energy - normally dumped through the waste-gate - can be converted into electric energy and used to push the car, by means of a second motor generator unit installed on the engine crankshaft (MGU-K). The goal of this paper is to assess pros and cons of the MGU-H technology when applied to a family of engines of different displacement, installed on a typical passenger car. The influence of engine size and cylinders layout is investigated, under the same set of hypotheses, considering both transient and steady engine operations. The baseline engine is a commercial 2.0 L, SI, 4-cylinder in-line, rated at 200 HP at 4500-5000 rpm. The study considers the following other SI configurations: a) 1.5L, 3-cylinder in-line, 150 HP; b) 3.0L, V6, 300 HP; c) 4.0L, V8, 400 HP; d) 6.0L, V12, 600 HP. It is assumed that all the 5 engines have the same unit displacement and the same maximum load, expressed in terms of brake mean effective pressure as a function of rotational speed. The study is carried out using an experimentally calibrated GT-Power model of the baseline engine, and considering the same class C vehicle. A Matlab/Simulink model is also developed for the analysis of the WLTP driving cycle. The study demonstrates that the MGU-H technology can be conveniently applied to all the considered engines. The maximum advantage in terms of fuel saving on a driving cycle is obtained on the smallest. However, in the V6, V8 and V12 configurations, the installation of one electric turbocharger instead of two, strongly simplifies the engine layout, and it allows the designer to find some space for additional powertrain components, such as electric motors, battery packs, etc. Moreover, the elimination of the turbo-lag problem, gives the designer much more freedom, enabling the adoption of more fuel efficient engine settings.