Experiment And Simulation Research On Double-Layer Diverging Combustion System Based On High Pressure Common Rail Fuel Injection

In order to optimize fuel distribution, oil and gas mixture to accelerate and enhance the utilization of the air in combustion chamber of conventional direct injection diesel engine. This group proposed a double-layers diffluent combustion chamber, by designing fuel spray impingement table to induce the fuel spray to the upper and lower in the combustion chamber to optimize fuel distribution, thereby increasing the diesel engine combustion efficiency.Combined with high pressure common rail fuel injection technology to optimization this combustion system is necessary. This paper is based on spray visualization test system of the research group and high pressure common rail fuel injection system, using the direct photograph method to study the spray spread and numerical simulation method to study the spray distribution and combustion by CFD software Converge in double-layers diffluent combustion chamber.By using injector calibration tests bench, experiments obtained the injector MAP of two different single hole injectors 0.16mm,0.18mm. Different injection pressure, nozzle diameter, environmental conditions, injection strategy were studied. Free spray tests showed that with the increase of the fuel injection pressure, spray penetration and spray extension area have shown significant increasing trend, while the spray angle has become smaller; with the same fuel injection pressure, the smaller was the nozzle diameter the greater were the spray penetration and spray expansion area, while the spray cone angle was bigger compared with hole injector 0.18mm at the beginning then smaller than it; with the increase of ambient temperature and pressure, liquid spray evaporation decreased and the amount of visible spray reduced; compared with a single injection, the fuel spray penetration and spray expansion area showed increasing with post injection strategy, and with the increasing of time intervals between main injection and post injection the trend was more obvious.For type ?, ? double-layers diffluent combustion chamber spray visualization tests showed that:under the same pressure of the fuel injection, the combustion chamber ? had a greater extension spray area and the spray fuel distribution was better; with the increase of the injection pressure, spray extension area showed a increasing trend; the influence of spray nozzle diameter on spray expansion area was not very clear and large diameter showed a slightly larger of spray extension area; with the increasing of engine load, fuel spray increased in the combustion chamber wall, especially on the guiding arc near the impingement table and the small area between the combustion chamber and cylinder cover, and for the lower temperatures and the weaker air flow, it is not conducive to evaporation and atomization of the fuel spray, so it is necessary to optimize fuel spray distribution in the up and down combustion chamber from designing of combustion chamber structure.Numerical simulation shows that:too deep of the combustion chamber hollow can cause the fuel spray gathering in the hollow; with a deeper hollow of type II combustion chamber, the vortex centers were more and smaller, and with a large upper space of the combustion chamber type I combustion chamber the vortex centers were less and larger; in the upper region of type I combustion chamber had high temperature region due to a large cluster distribution of fuel spray; high temperature area of type II combustion chamber was narrow and longer due to the presence of the hollow.