Improvement of the Dynamic Characteristic of an Automotive Engine by a Turbocharger Assisted by an Electric Motor

Abstract

Abstract Increase of the mean effective pressure in an automotive Diesel engine is generally the consequence of the turbocharging and subsequent charge cooling of the working medium. A problem of poor performance during the engine speed and load change is attributed to the nature of energy exchange between the engine and the turbocharger. Filling of the intake and exhaust manifolds, consequent increase of the pressure and acceleration of the rotating components of the turbocharger require a certain period of time. Dynamic performance of the turbocharger can be substantially improved by the assistance of an electric motor attached directly to the turbo shaft. A new concept of asynchronous electric motor with a very thin rotor was applied to support the turbocharger during the transient regimes of the engine. Experimental work for matching an electrically assisted turbocharger to an engine is rather expensive; it was therefore decided to determine general characteristic of the electric motor separately by experiments, whereas transient response of the turbocharged and intercooled Diesel engine was simulated by a zero-dimensional filling and emptying computer simulation method. A lot of experimentally obtained data and empirical formulae for the compressor, gas turbine, flow coefficients of the engine valves, intercooler, high pressure fuel pump with the pneumatic control device (LDA), combustion parameters etc. were applied to overcome deficiency introduced by the zero-dimensional simulation model. As the result a reliable and accurate program compatible with the experimental results in steady and transient engine operation was developed and is presented in the work. Faster transient response of the engine was obtained by applying an electric motor to assist the turbocharger; a few versions were introduced in the simulation program and were also analysed in the work.