Partially premixed combustion based on different injection strategies in a light-duty diesel engine

• Single and multiple injection strategy were investigated to achieve partially premixed combustion (PPC).
• Single early injection mode shows the characteristics of both premixed and low temperature combustion.
• The pilot-main injection interval and pilot injected mass were adjusted to achieve PPC.
• The BSFC and thermal efficiency are both improved in pilot injection mode at low load.
• The multi-injection strategy achieved PPC with smaller cylinder pressure and lower peak pressure rise rate.

The performance of partially premixed combustion (PPC) relies heavily on the proper mixing between the fuel and the in–cylinder gas. In this paper, two injection strategies, including single and multiple injection, were investigated to achieve PPC in a four-cylinder light-duty diesel engine, and were evaluated in terms of heat release rate, combustion phase, emissions and thermal efficiencies. The combustion process is dominated by premixed combustion and the diffusion combustion process is quite short at the early single injection mode. It shows the characteristics of both premixed combustion and low temperature combustion. However, the ratio of diffusion combustion increases at high load. NOx and smoke emissions reduce at the same time with late injection mode. For the multiple injection strategy, the cylinder pressure and peak pressure rise rate is lower. As the pilot-main interval increases, the mixture is more homogeneous due to sufficient premixing time. However, diffusion combustion plays the dominant role in the double pilot injection mode. The BSFC (brake specific fuel consumption) and brake thermal efficiency are considerably improved with pilot injection mode at low load condition, compared with late injection mode. The NOx decreases dramatically in double pilot injection PPC, while the smoke and CO increase, compared with single early injection mode.