Experimental and numerical studies on fuel-film combustion and wall thermal effect of diesel spray

Given a lack of clarity on fuel-attached combustion and its effect on the wall heat load in diesel engines remain to be clarified. Therefore, visualization and wall temperature measurement experiments are carried out in a constant volume combustion chamber, while CONVERGE simulation is performed to make further explanation. The fuel film attached to the wall is successfully ignited by the acetylene premixed flame, which confirms the occurrence of the wall-attached combustion inside the engine. Although the natural luminance of the fuel film flame shows no significant difference from the conventional impingement spray, it burns quietly and lasts nearly 100 ms, which is much longer The fuel film flame is a near-flat layer on the wall, progressing slowly due to simultaneous burning and evaporation. With the increase of injection pressure and fuel mass, the flame area and natural luminance show an upward trend due to enhanced fuel adhesion. Immediately after the fuel film is burned, there is a substantial heat load applied the wall, even exceeding the bearing limit of the aluminum alloy. As fuel mass rises sharply from 17 mg to 85 mg, the peak wall temperature increases from 563 K to 873 K. Besides, the high temperature of the wall lasts for an extremely long period of time, coupled with an upward shift of peak heat flux from 8 MW/m² to 16 MW/m² as the injection pressure rises from 40 MPa to 100 MPa. By establishing the chain mechanism of fuel film-combustion-heat load, the present study contributes an solution to further study in this area.