| Since the birth of internal combustion engine, it has been widely applied because it has brought great convenience for people’s life, but the energy and environmental issues have been becoming increasingly prominent, so more and more strict emission regulations have been formulated. These put forward a higher requirement for the optimization of the working process and the control of emissions of engine. The quality of fuel spray, which affects the quality of mixture formation directly and has influence on engine combustion and emissions, is the most important part of the working process of engines. Related research have showed that the physicochemical characteristics of fuel, spray control conditions and spray boundary conditions have huge impacts on the spray of fuel. The design of fuel, which means the improvement of the physical and chemical characteristics of fuel, is an important means to optimize the quality of spray, organize combustion properly and reduce emissions of engines. Therefore, the spray characteristics of fuel on conditions of different fuels, different spray conditions and different spray boundary conditions have been simulated in this paper with fuel of gasoline / diesel blends, and the influences of gasoline / diesel blends on the performance of compression ignition engine were also experimentally studied.In order to realize the optical measurement of the spray characteristics of fuels, a visual constant volume spray test system has been designed. The system mainly consists of constant volume vessel, fuel supply system, intake and exhaust system, control system and optical testing system. And the strength of the key part of the system, the constant volume vessel, has been simulated and experimentally checked, this ensured the feasibility, safety and reliability of the system.In order to study the influences of fuel properties, spray control conditions and boundary conditions on the spray characteristics, a fuel spray model under the condition of evaporation in the vessel was built by AVL-Fire. The distribution of spray construction, spray penetration and Sauter mean diameter and related field of gasoline / diesel blends were studied. The results showed that with the proportion of gasoline blended in diesel increased, the maximum spray penetration distance was shortened, the time of spray penetration distance reached the maximum was shortened, the SMD decreased. The analysis results of temperature field showed that the low temperature region mainly occurred in the middle part and the front part of the spray, adding gasoline to the mixed fuel is beneficial to the atomization and evaporation of fuel. To different fuels, the largest gas velocity occurred in the central axis of the spray, the speed of oil on both sides of the spray was low, G50 fuel, which has a large gasoline blending ratio, had a minimum velocity on both sides of the spray. With the increase of fuels’ temperature, the viscosity of blended fuel declined in degrees, the maximum penetration decreased and the SMD decreased. With the increase of injection pressure, the spray penetration rate increased, the time of the maximum spray penetration occurred was advanced continually, the penetration peak decreased, the SMD value decreased, the non-diesel components evaporated rapidly in the early period of the spray, the effect of atomization was improved continually. With the increase of the nozzle diameter, the spray penetration and the SMD increased significantly, when a little nozzle diameter was used, the promotion effect of the evaporation of the non-diesel components in blended fuel was obvious. With the increase of the environment pressure, the maximum spray penetration is shortened obviously and the SMD value decreased. The effect of ambient temperature on the spray penetration distance was continuous, in the development stage of the spray, with the increase of environment temperature, the spray penetration increased quickly, in the stabilization stage of spray, the spray penetration of spray in high ambient temperature was shortened conversely, the value of SMD increased.Based on the research of the spray characteristics of gasoline / diesel blends, the effects of gasoline / diesel blends on the combustion and emission of engine under different boundary conditions were studied. The results showed that the effect of spray characteristics of gasoline / diesel blends on the combustion and emission of engine is significant. In light and medium load conditions, the engine has lower pressure and temperature in cylinder, poorer injection quality, longer ignition delay period,shorter combustion duration period and higher emission of CO, HC and smoke. Under medium and high load conditions, with the increasing of gasoline mixture ratio, the uniformity of the working fluid in the cylinder was improved and smoke emission reduced, but the NOx emission increases. With the increase of injection pressure, the spray penetration was shortened, the droplet diameter was decreased, which was beneficial to the atomization, evaporation and mixing of fuel, the amount of premixing was increased, the ignition delay and the combustion duration was shortened, the smoke emission decreased, but the NOx emission increased. The CO and HC emissions increased when blended fuel with high blending ratio of gasoline was used. The injection timing mainly affected the temperature and pressure in the cylinder, the pressure and temperature in the cylinder at the time of injection increased, the ignition delay period reduced, combustion phase delayed, the maximum combustion pressure decreased, the combustion duration period and pressure rise rate decreased slightly, NOx emissions significantly reduced with the injection delay increased, but mixed fuel with a high blending ratio of gasoline has higher NOx emissions... |
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