The injection nozzle inclination angle affects the flow characteristics in nozzle holes. Stroboscopic photographs of instantaneous spray plumes show that the length of each spray plume is different. Test results show that the fuel quantities injected from the holes are remarkably less when the nozzle hole spray angle relative to the injection nozzle axis is smaller compared with others with the same hole diameter. Hence, the authors analyzed the flow characteristics in injection nozzles using a computational fluid dynamic technique. Calculation results show good qualitative agreement with experimental results.INJECTION NOZZLES are normally installed in a two-valve cylinder head with an inclination angle. As shown in Fig. 1, the spray angle of each nozzle hole is different in order to maintain the same impingement height against the piston cavity for each spray. Stroboscopic photographs of instantaneous spray plumes show that the fuel spray injected from holes, whose spray angles relative to the injection nozzle axis are smaller, have different spray characteristics compared to others. For example, an unsteady narrower and shorter spray plume. The reduction of this spray plume variation leads to improvements in the combustion of direct injection diesel engines. Experimental flow visualization of the flow in a nozzle is practically impossible because of the high pressure flow in a small space. Hence, the authors analyzed the flow characteristics in the injection nozzle using a computational fluid dynamic (CFD) technique and investigated the effects of several parameters on the flow characteristics in nozzle hole area.