Experimental Study On Spray And Combustion Characteristics Of V-Type Intersecting Hole Nozzle And In Double-Layer Diverging Combustion System

In order to reduce local equivalence ratios in traditional diesel combustion and increase the mixing rate, intersecting hole nozzle and double-layer diverging combustion system were proposed to intensify turbulence and diffusion in the spray respectively, thereby reducing soot emissions and raising combustion efficiency. Therefore it is necessary to obtain a comprehensive and fundamental understanding of spray and combustion characteristics of intersecting hole nozzle and in double-layer diverging combustion system so as to optimize designs of them.This experimental study was conducted on a self-built spray and combustion visualization test bench. Direct spray photography and flame natural luminosity method were used to determine free spray and combustion characteristics of intersecting hole nozzle and impinging spray and combustion characteristics in double-layer diverging combustion system.In the experiment based on intersecting hole nozzle, two intersecting hole nozzles with different intersecting angles and one single hole nozzle was tested. Spray characteristics were investigated in terms of the effects of injection pressure, ambient gas density and ambient temperature, while combustion characteristics were investigated under different injection pressures. The experimental results showed that compared with in the case of single hole nozzle, under intersecting hole nozzle conditions, spray penetration was smaller and frontal and side spray angles were larger; these differences became greater with increasing of intersecting angles in intersecting hole nozzles and lifting of injection pressures. The effect of ambient gas density on spray penetration and spray angle was greater in the case of intersecting hole nozzle; the effect of ambient temperature was in the same case, indicating better atomization performance of the spray injected from intersecting hole nozzles. Under lower injection pressures the ignition delay in the case of intersecting hole nozzles was longer, with the difference from single hole nozzle less evident under higher injection pressures. The integral flame intensity was lower under intersecting hole nozzle conditions, implying lower soot level, and this phenomenon became more prominent with lifting of injection pressure and intersecting angle.In the experiment based on double-layer diverging combustion system, two-dimensional combustion chamber models were utilized to simulate ω combustion chambers and double-layer diverging combustion chambers. The investigation was done in terms of comparison of the two types of combustion chambers, the effect of injection pressure and the effect of piston position. The results from the comparison of the combustion chambers showed that the shape of lower layer of the double-layer diverging combustion chamber could prevent from wall wetting. The injected fuel was denser on the impinging circular surface and in the squish region in the double-layer diverging combustion chamber, while at the bottom of the piston bowl and over the piston bowl rim in the co combustion chamber, where there was nearly no fuel in the squish region. In the double-layer diverging combustion system fuel was burned in two layers, with upper layer flame brighter and lasting longer; for co combustion chamber, combustion occurred mostly in the piston bowl and flame entered squish region limitedly. Because of more intense spray diffusion in the double-layer diverging combustion system, the scaled flame area therein was larger under middle load, while under high load, the scaled flame areas were at the same level. The results from the study focused on the double-layer diverging combustion system showed that increasing injection pressure and leading the spray to impinge on the impinging circular surface could lead to faster evaporation. The fuel distribution was basically the same at the end of injection under different injection pressures. The higher the injection pressure was, the shorter the ignition delay was and the faster the combustion process went. Different piston positions at different injection timings determined the fuel distribution in the two layers, thus determining flame distribution.