Effect of pilot nozzle orientation and injection timings on combustion and emission characteristics of diesel/methanol JCCI engine

Methanol fuel is difficult to directly ignite due to its low cetane number, making Jet-Controlled Compression Ignition (JCCI) with diesel ignition a promising solution. However, the interaction mechanisms remain unclear, limiting higher thermal efficiency and further reducing carbon emissions. To explore this, the effects of the diesel angle (θd) and the injection timings of diesel and methanol (tSOI,d and tSOI,m) on interactions, flame development, in-cylinder combustion, and emissions are investigated numerically. The results reveal that the combustion structure significantly influences engine performance, revealing two distinct modes as the diesel injector angle (θd) decreases: Central Ignition (CI) and Peripheral Ignition (PI). The PI mode involves multiple dispersed diesel jets forming ignition points at the cylinder periphery, leading to stochastic ignition position. An improper θd can hinder effective methanol contact, reducing efficiency. This mode is notably influenced by injection timing, impacting combustion stability while having a limited effect on CA50-CA10. In CI mode, the diesel fuel accumulates in the blank region surrounded by methanol, facilitating stable ignition and accelerating combustion. However, too small θd can cause increased moving distance, resulting in position deviation and prolonged combustion, while appropriate θd improves indicated thermal efficiency (ITE) with minimal sensitivity to injection timing. The optimal diesel angle achieves 0.53% increase in ITE while reducing unburned methanol (63.7%) and HC (75%) emissions. These findings suggest that optimizing multipoint diesel distribution in a methanol-saturated environment can enhance thermal efficiency and reduce emissions, providing valuable insights for the design of methanol engines.