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Parametric Study on Electric Turbocharging for Passenger Cars
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
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 point of this paper is to assess pros and cons of the MGU-H technology when applied to road engines of different size. It is far from clear if the expected advantages in terms of car performance and fuel efficiency are worth the effort of introducing such a complex and expensive technology. Moreover, the effect of engine size should be carefully investigated, considering both transient and steady engine operations. The baseline engine is a commercial 2.0 L, 4-cylinder in-line, rated at 200 HP at 5000-6000 rpm. The study considers the following other 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, W12, 600 HP (three banks of cylinders, forming an angle of 60° between each bank, one crankshaft with 4 throws). 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 driving cycles (NEDC, WLTP). The study demonstrates that the maximum advantage in terms of fuel saving on a driving cycle is obtained on the smallest engine. However, in the V6, V8 and W12 configurations, the installation of one electric turbocharger, instead of two or three conventional turbochargers, 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.