Spark-ignition direct-injection (SIDI) gasoline engine, especially in downsized boosted engine platform, has proven to be one of the most promising concepts to improve vehicle fuel economy. SIDI engines are also getting a larger share of the gasoline engine market which is traditionally dominated by the port fuel injection (PFI) engines in the U.S., European and Chinese vehicles. However, higher particle number emissions associated with operating the engine at higher loads pose additional challenges for meeting future stringent emissions regulations. In this study, the potential of using multiple injection strategies (double injection and triple injection strategy during the intake stroke in homogeneous combustion mode) to reduce particle number emissions in a 2.0 liter boosted SIDI gasoline engine at 1000 rpm, 11 bar BMEP condition was investigated using Horiba MEXA SPCS1000 PN measurement instrument. To clarify the mechanism for the particle emissions benefit by multiple injection strategies, three-dimensional (3D) Computational Fluid Dynamics (CFD) model of the in-cylinder process was realized using CONVERGE software with the inputs from GT-Power® engine simulation.
Measurements indicate that the double injection strategy causes a 60% reduction in particle number concentration and up to 80% reduction when implementing triple injection strategy as compared to baseline single injection strategy, demonstrating the potential of multiple injections as a promising strategy for lower particle emissions at high load operating conditions. The 3D CFD simulation reveals that double injection is beneficial to the reduction of spray-piston and spray-liner impingement, and the improvement in mixture preparation process, resulting in lower levels of particles. For triple injection strategy, the spray impingement is further reduced, and the fuel is better mixed with air, leading to a significant reduction in particle formation. Regardless of double injection and triple injection strategy, the particle number emissions tend to increase when retarding the final injection timing. While, reducing the first injection mass is beneficial for lower particle number emissions both for double injection and triple injection strategies during the intake stroke.
