Optimization of Injection Rate Shape Using Active Control of Fuel Injection

The effect of injection rate shape on spray evolution and emission characteristics is investigated and a methodology for active control of fuel injection is proposed. Extensive validation of advanced vaporization and primary jet breakup models was performed with experimental data before studying the effects of systematic changes of injection rate shape. Excellent agreement with the experiments was obtained for liquid and vapor penetration lengths, over a broad range of gas densities and temperatures. Also the predicted flame lift-off lengths of reacting diesel fuel sprays were in good agreement with the experiments. After the validation of the models, well-defined rate shapes were used to study the effect of injection rate shape on liquid and vapor penetration, flame lift-off lengths and emission characteristics. A consistent trend was observed over the entire range of densities and temperatures, which lead to the conclusion that the fuel distribution can be controlled by modifying the injection rate shape. Since it is believed that the NOx and soot emissions are substantially affected by the equivalence ratio distribution of the gas mixture prior to the combustion, the variation of fuel distribution via the modification of injection rate shape offers a useful way of emission control. From the knowledge gained by this study, a control approach was devised to maintain the local equivalence ratios below a certain level using active control of fuel injection, thus preventing soot formation.