With the increase in the number of automobiles on road, there is a very strong emphasis on reducing the air pollution which led to evolution of stringent emission norms. To meet these stringent emission norms, the ideal solution is to optimize the engine hardware and the combustion system to reduce the emission at source thereby reducing the dependency on exhaust after treatment system.
Gasoline Direct Injection (GDI) engines are gaining popularity worldwide as they provide a balance between fun to drive and fuel efficiency. Controlling the particle emissions especially Particle Number (PN) is a challenge in GDI engines due to the nature of its combustion system.
In this study, experiments were performed on a 1.2Litre 3-cylinder 250bar GDI engine to capture the effect of injection strategies on PN. Single injection, two injection split and three injection split sweeps were done at different operating points and coolant temperatures to identify the best injection timing with respect to PN emissions, combustion stability (IMEP COV) and Brake Specific Fuel Consumption (BSFC). From the study it could be inferred that the optimum number of injections is dependent on the speed and load and the injection strategy must be defined separately for different engine operating conditions. Also, it was found that the dependency injection strategy on particulate emissions was more on cold engine conditions when compared to hot engine conditions. Liner & Piston wetting can be reduced with multiple injection strategy, by placing a fourth of the fuel into the split quantity. Optimized multiple injection strategy ensures no piston & liner wetting which prevents soot flame formation & reduces engine out PN.
Experimental results show that with multiple injection strategy the particulate emissions reduced by 10% on overall engine operating points. This improvement is more predominantly witnessed at cold engine temperature.