Study on impinging ignition and wall-attached fuel film combustion characteristics of light- to heavy-duty diesel engines at low temperatures

The difference in impinging ignition characteristics of light- to heavy-duty diesel engines at low temperatures and the heating effect of fuel film combustion on the wall are still not well understood. Thus, visualization experiments are conducted in a constant volume combustion chamber using Mie-scattering and direct photography methods, and 3-D simulation is used to supplement and explain the experimental phenomena. The results show that the autoignition initiates in the free spray and then hits the wall for the 0.12 mm nozzle. However, 30% of the liquid fuel under the 0.32 mm nozzle adheres to the wall, and the cooling effect causes the evaporation rate to decrease by orders of magnitude. The mixture at the initial flame is mainly distributed in the low-temperature and low-concentration region, and coupled with the excessive fuel diffusion caused by spray-wall interaction, the transition from the cool flame to hot flame is severely slowed down. With the increase of nozzle diameter from 0.12 mm to 0.32 mm, the hot flame position shifts from the fuel-rich side to the fuel-lean side, the flame fluctuates greatly and the area decreases, and the critical ignition temperature increases from 753 K to 793 K. When the wall-attached fuel accumulated in a misfire or an unstable ignition condition is ignited again, the combustion lasts for nearly 100 ms. As the nozzle diameter increases from 0.12 mm to 0.32 mm, the peak wall temperature rises from 487 K to 556 K, and the heat flux increases nearly twice, which inevitably increases the heat load of the wall.