Vladimir Medica

Improvement of the dynamic characteristic of an automotive engine by a turbocharger assisted by an electric motor

Turbocharging and subsequent charge cooling of the working medium usually causes increase of the mean effective pressure in an automotive diesel engine. Poor performance during the engine load increase is attributed to the nature of energy exchange between the engine and the turbocharger. Filling of the intake and exhaust manifolds, as well as 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 means 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 operation of the engine. The experimental work of matching an electrically assisted turbocharger to an engine is rather expensive; it was therefore decided to determine general characteristic of the electric motor separately through 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, i.e., better load acceptance of the engine was obtained by applying an adequate electric motor to assist the turbocharger; three versions of electric motors with different torque to mass moment of inertia ratios and different operating regimes were introduced in the simulation program to investigate their influence on the transient behavior of the engine.

An Analysis of Turbocharged Diesel Engine Dynamic Response Improvement by Electric Assisting Systems

It is well known that turbocharged diesel engines suffer from an inadequate response to sudden load increase, this being a consequence of the nature of the energy exchange between the engine and the turbocharger. The dynamic response of turbocharged diesel engines could be improved by electric assisting systems, either by direct energy supply with an integrated starter-generator-booster (ISG) mounted on the engine flywheel, or indirect energy supply with an electrically assisted turbocharger. A previously verified zero dimensional computer simulation method was used for the analysis of both types of electrical assistance. The credibility of the data presented is further assured by the experimentally determined characteristics of the electric motors used as input parameters of the simulation. The paper offers an analysis of the interaction between a turbocharged diesel engine operating under various load conditions and electric assisting systems, as well as the requirements for supporting electric motors suitable for the improvement of an engine’ s dynamic response. It is evident that an electrically assisted turbocharger outperforms an integrated starter-generator-booster for vehicle application, however ISG is the preferred solution when instant power increase is demanded.

Simulation of a Two-Stroke Slow Speed Diesel Engine Using a Quasi-Dimensional Model

The paper describes a diesel engine quasi-dimensional numerical model, implemented in a previously developed 0D model. The presented model uses direct solution to the conservation equations set for cylinder pressure and zone temperatures without numerical iterations which are customary in these models. Numerical model validation was performed on a four-stroke diesel engine at four operating points. After successful validation, modifications were implemented in the numerical model allowing the simulation of a marine two-stroke diesel engine. It is important to emphasize that the simulation model logic remained unchanged. The only significant differences are the changes in the engine working processes and different calculation of the engine operating parameters which are characteristic of two-stroke engines. The results of the diesel engine simulations using the quasidimensional model were compared to the test-bed measurements of the two-stroke engine found in available literature. Good agreement between the measurements and the simulation results for the two-stroke engine has been obtained. The developed quasi-dimensional numerical model can accurately predict operating parameters of the four-stroke and the twostroke diesel engine.

Quasi-dimensional diesel engine model with direct calculation of cylinder temperature and pressure

Original scientific paper This paper describes the quasi-dimensional numerical model, implemented in previously developed 0D model. The presented model uses direct solution of equations for cylinder pressure and zone temperatures, without numerical iterations which are customary for these models. In the model there is shown a process of averaging from a set of small fuel spray packages (volumes) into big ones, which is a necessary precondition for the numerical stability. The model uses about fifty submodels. Simulations were performed in eight operating points, on four most sensitive engine cylinder operating parameters. Direct solution of temperature and pressure changes, in conjunction with the fuel spray packages averaging, represents a contribution to quasi-dimensional diesel engine process modelling.