Yuhei Matsumoto

An investigation of mixture formation and in-cylinder combustion processes in direct injection diesel engines using group-hole nozzles:

Abstract Mixture properties of the transient fuel spray injected by group-hole nozzles were quantitatively studied in a constant volume chamber via the laser absorption scattering (LAS) technique, and compared with conventional single-hole nozzles. Specific areas investigated included non-evaporating and evaporating ambient conditions, and the conditions of free spray and spray impinging on a flat wall. The particular emphasis was on the effect of one of the key parameters of the group-hole nozzle structure, namely, the interval between orifices. Subsequently, in-cylinder ignition and combustion processes were investigated by direct flame visualization in a single-cylinder optical research engine using the group-hole nozzle and the standard multi-hole nozzle, together with heat release analysis. Results show that the group-hole nozzle can produce a smaller Sauter mean diameter (SMD) of droplets under the non-evaporating condition. Under the evaporating condition, for the free spray cases, there exists a trade-off between the fuel evaporation and the spray penetration in the application of the group-hole nozzle. With the increase in interval between orifices, the ratio of evaporation increases, but the spray tip penetration decreases. For the spray impinging on a flat wall, the group-hole nozzle can enhance the spray tip penetrations to some extent compared with the single-hole nozzles. Flame images taken in a direct injection optical engine show that the enhancement of the fuel atomization and evaporation by the group-hole nozzle may contribute to a decrease in overall flame luminosity level, suggesting reduced soot formation in diesel engines.

Improving diesel mixture preparation by optimization of orifice arrangements in a group-hole nozzle:

Abstract The factors affecting the free and wall-impinging spray characteristics of closely spaced micro-orifices (group-hole nozzles) are investigated to determine the optimal orifice arrangement for improved in-cylinder air utilization. To determine the optimized arrangement of the nozzles, different types of group-hole nozzles with different intervals and angles between the orifices have been studied. The spray tip penetration and fuel evaporation were analysed using a laser absorption scattering technique for non-axisymmetric sprays. In the case of a free spray, the spray tip penetration of the group-hole nozzle increased as the included angle and the distance between orifices decreased. The shortest spray tip penetration was observed when the two jets injected by a group-hole nozzle began to separate, but the periphery of each jet still touched. On the contrary, fuel evaporation deteriorated when the distance and angle between the two orifices decreased since the severe collision/coalescence of the two jets hindered evaporation. In the case of a wall-impinging spray, the spray tip penetration of the group-hole nozzle was strongly related to the distance χ between the arbitrary centres of each jet at the impingement wall. Maximum spray tip penetration of the group-hole nozzle was observed at a specific range of χ. In this range, the strong momentum regions of the jets began to meet just after wall impingement, therefore collision/coalescence before wall impingement was minimized and the interaction between the two wall-impinging jets was maximized. The fuel evaporation in the wall-impinging spray also improved at a distance of χ for maximum tip penetration. The mechanism causing this phenomenon is discussed in terms of near-field spray interaction and wall-impinging jet interaction after wall impingement.