In the present paper the status of development of diesel combustion and pollutants formation modeling at Diesel Engines and Fuels Research Division of Instituto Motori is pointed out. The main features and performances of the model are discussed comparing the numerical results with some experimental data. For the experiments, a single-cylinder direct-injection diesel engine was used. In the head of the engine two small quartz windows have been mounted, in order to obtain pictures of the injection and combustion processes by high-speed cinematography, and to apply the two color technique for soot temperature and soot loading measurements. The soot loading was measured by the two color technique and the a priori and the experimental uncertainties of the measurement technique were carefully evaluated. In addition, the engine may be also equipped with a second head, in which a fast acting valve allows the direct sampling of the combustion products. To simulate the diesel engine combustion, the Kiva II code, with some improvements, was used. In particular, a hybrid model based on both WAVE and TAB models was adopted for jet break up modeling, and a spray wall impaction model was added to the original code. New combustion and soot models were also set up. The main features of the models are the following: the liquid fuel injection vaporization and dispersion is computed as provided by the Kiva II code routines; the fuel vapor undergoes conversion to acetylene by a single-step reaction. The acetylene formed is oxidized at high temperature by a single-step stoichiometric reaction with mean rate defined as in standard E.B.U. combustion models. Simultaneously with the acetylene combustion a three-step soot formation and oxidation model performs the soot loading computations for each computational cell jointly with a modified Zel'dovich mechanism for NO computations. The computational results demonstrate that the proposed model, represents the main features of the diesel combustion, despite the strong simplifications introduced. However, further work is required to obtain a satisfactory predictivity of multi-dimensional models of combustion and exhaust emission.
An assessment of predictivity of CDF computations of combustion and pollutants formation in d.i. Diesel
Beatrice C;Belardini P;Bertoli C;Del Giacomo N
1996
Abstract
In the present paper the status of development of diesel combustion and pollutants formation modeling at Diesel Engines and Fuels Research Division of Instituto Motori is pointed out. The main features and performances of the model are discussed comparing the numerical results with some experimental data. For the experiments, a single-cylinder direct-injection diesel engine was used. In the head of the engine two small quartz windows have been mounted, in order to obtain pictures of the injection and combustion processes by high-speed cinematography, and to apply the two color technique for soot temperature and soot loading measurements. The soot loading was measured by the two color technique and the a priori and the experimental uncertainties of the measurement technique were carefully evaluated. In addition, the engine may be also equipped with a second head, in which a fast acting valve allows the direct sampling of the combustion products. To simulate the diesel engine combustion, the Kiva II code, with some improvements, was used. In particular, a hybrid model based on both WAVE and TAB models was adopted for jet break up modeling, and a spray wall impaction model was added to the original code. New combustion and soot models were also set up. The main features of the models are the following: the liquid fuel injection vaporization and dispersion is computed as provided by the Kiva II code routines; the fuel vapor undergoes conversion to acetylene by a single-step reaction. The acetylene formed is oxidized at high temperature by a single-step stoichiometric reaction with mean rate defined as in standard E.B.U. combustion models. Simultaneously with the acetylene combustion a three-step soot formation and oxidation model performs the soot loading computations for each computational cell jointly with a modified Zel'dovich mechanism for NO computations. The computational results demonstrate that the proposed model, represents the main features of the diesel combustion, despite the strong simplifications introduced. However, further work is required to obtain a satisfactory predictivity of multi-dimensional models of combustion and exhaust emission.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
