Effects of ratio and dwell of split injection on fuel spray and mixture formation process under evaporating, non-reacting condition

The effects of split injections of a diesel spray was evaluated in a constant volume chamber under evaporating, non-reacting condition. Laser absorption scattering (LAS) technique was utilized for the mixture concentration measurement, using a diesel surrogate fuel consists of n-tridecane and 2.5% of 1-methylnaphthalene in volume basis. While fixing the total injected fuel mass of 5.0 mg/hole, the effects of split ratio in mass basis and the dwell time (or injection interval) were investigated. Among the split ratios conducted in the current study (3,7, 5:5 and 7:3), the split ratio of 7:3 was the optimum for lean mixture formation regarding the overall distribution of the equivalence ratio at end-of-injection (EOI) timing. The air entrainment wave at the EOI timing of the first injection allowed the fuel at the vicinity of the nozzle to become leaner at a faster rate. It was thought that, the split ratio of 7:3 provided an adequate amount of fuel quantity and vapor penetration to fit into the fuel-lean region formed from the first injection. The increase of the dwell time provided longer time for leaner mixture formation of the first injection, but the improvement was small. Therefore, the shortest dwell of 120 μs was reasonable for lean mixture formation of the second spray. It showed similar equivalence ratio distribution compared to any other longer dwell time conditions under the absence of combustion.