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C. Rustin:
"Investigation of model parameters for the part load simulation of a gasoline engine";
Supervisor: B. Geringer, T. Lauer; E 315 Institut für Verbrennungskraftmaschinen und Kraftfahrzeugbau, 2004.

A parameter adaptation of a full load model of a spark ignition gasoline engine was realized to simulate the part load operation of this motor between 1000 rpm and 3500 rpm. The study of the variation of these parameters was realized by means of the one-dimensional simulation BOOST software. The air fuel mixture was always stoichiometric. The accuracy of the model was adjusted and verified with test bench results.
A thermodynamic single-zone cylinder model was used to model the combustion, the wall heat transfers and the gas exchange in the combustion chamber. The Vibe parameters were determined from post-processed experimental data. The empirical mean friction pressures were introduced. The model boundary conditions (temperature and pressure) also came from experiments. Realistic wall temperatures were assumed for the engine and the exhaust pipes. And calibration factors allowed to adjust the heat transfers. In order to find a good correlation between the experimental and simulated averaged values and variations of the exhaust pressure upstream the catalyst, the predefined BOOST catalyst element had to be replaced by a plenum. In this way, the gas exchange was simulated accurately enough. The reflections of the pressure waves and the resonance at 3000 rpm were modelled in the exhaust system thanks to the outlet restriction of the plenum and the volume not "closing" the exhaust pipes, respectively. The flow coefficients of the intake throttle and catalyst outlet restrictions allowed to adjust the brake mean effective pressure and the averaged value of the exhaust pressure.
The gas exchange losses during the part load operation are related to the partial closure of the intake throttle. It was possible to simulate this throttling resulting in increase of pumping losses at engine speed constant and at brake mean effective pressure constant.
The internal exhaust gas recirculation carried out by valves timing changes is a possible remedy to improve the part load operation. BOOST permitted the modelling and the study of the valves timing changes with a rather good accuracy.
However, the higher exhaust gas concentration, depending on the valves timing, decelerates combustion. To increase the velocity of the flame propagation a variable-swirl-tumble technology is employed in the engine. The swirl throttle, closed, may bring a slight fuel economy benefit, but mainly it allows use of high levels of valve overlap or exhaust gas recirculation while still giving a stable burn. For the valves timing considered it was impossible with the experimental model to simulate the slight decrease of the brake specific fuel consumption and the theoretical increase of the heat losses for the operation at swirl throttle closed. This represents a limitation of the null-dimensional thermodynamic model used to model the different phenomenons in the combustion chamber. It is unable to take into account the increase of the kinetic energy, the turbulence and the swirl and tumble movements in the cylinder and thereby to preview the effects of the closure of the swirl throttle.