The combustion process of a Port Fuel Injection (PFI) engine is deeply influenced by the mixture formation process. The needs of reducing engine emission and fuel consumption push the engine manufactures to implement new advanced experimental and numerical techniques to better control the mixture quality. The local mixture air-index at the spark plug is closely related to combustion instabilities and the Indicated Mean Effective Pressure (IMEP) Coefficient of Variation (CoV) well correlates with the variability of the flame kernel development. The control of air to fuel ratio is especially critical for high performance engines: due to the low stroke-to-bore ratio the maximum power is reached at very high regimes, letting little time to the fuel to evaporate and mixing with air. The injector located upstream the throttle causes a lot of fuel to impinge the throttle and intake duct walls, slowing down the dynamics of mixture formation under part load conditions. The aim of the paper is to present a multi-cycle methodology for the simulation of the injection and the mixture formation processes of high performance PFI engine, in order to evaluate both the quality of combustion and the fuel dynamics in the intake duct. The phenomena involved in the process are highly heterogeneous, and particular care must be taken to the choice of CFD models and their validation. In the present work all the main models involved in the simulations are validated against experimental tests available in the literature, selected based on the similarity of physical conditions of those of the engine configuration under analysis. The lagrangian spray is initialized with a semi-empirical methodology, based on available experimental data, and its interaction with the wall is simulated by means of the Kuhnke model, so to take into account the high wall temperature of the intake valves during impingement. The dynamics of the wall film are accurately represented by the activation of momentum equation of wall film and a validation of its dynamics is accomplished against proper test cases. The methodology is applied in two different engine configurations with separate objectives: a part load condition, where the dynamics of fuel in the intake duct is crucial to ensure drivability, a full load configuration, for the evaluation of mixture quality and combustion stability. © 2013 The Authors.
Evaluation of the Mixture Formation Process of High Performance Engine with a Combined Experimental and Numerical Methodology
FORTE, CLAUDIO;BIANCHI, GIAN MARCO;CORTI, ENRICO;
2014
Abstract
The combustion process of a Port Fuel Injection (PFI) engine is deeply influenced by the mixture formation process. The needs of reducing engine emission and fuel consumption push the engine manufactures to implement new advanced experimental and numerical techniques to better control the mixture quality. The local mixture air-index at the spark plug is closely related to combustion instabilities and the Indicated Mean Effective Pressure (IMEP) Coefficient of Variation (CoV) well correlates with the variability of the flame kernel development. The control of air to fuel ratio is especially critical for high performance engines: due to the low stroke-to-bore ratio the maximum power is reached at very high regimes, letting little time to the fuel to evaporate and mixing with air. The injector located upstream the throttle causes a lot of fuel to impinge the throttle and intake duct walls, slowing down the dynamics of mixture formation under part load conditions. The aim of the paper is to present a multi-cycle methodology for the simulation of the injection and the mixture formation processes of high performance PFI engine, in order to evaluate both the quality of combustion and the fuel dynamics in the intake duct. The phenomena involved in the process are highly heterogeneous, and particular care must be taken to the choice of CFD models and their validation. In the present work all the main models involved in the simulations are validated against experimental tests available in the literature, selected based on the similarity of physical conditions of those of the engine configuration under analysis. The lagrangian spray is initialized with a semi-empirical methodology, based on available experimental data, and its interaction with the wall is simulated by means of the Kuhnke model, so to take into account the high wall temperature of the intake valves during impingement. The dynamics of the wall film are accurately represented by the activation of momentum equation of wall film and a validation of its dynamics is accomplished against proper test cases. The methodology is applied in two different engine configurations with separate objectives: a part load condition, where the dynamics of fuel in the intake duct is crucial to ensure drivability, a full load configuration, for the evaluation of mixture quality and combustion stability. © 2013 The Authors.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
