Visualization on Combustion Characteristics of Common Rail Diesel Engine at Different Injection Pressures

Abstract:

In a constant volume combustion chamber combined with high pressure common rail system, the ignition, combustion and soot formation characteristics of diesel were studied at different injection pressures keeping injection pulse width or fuel injection volume constant. The change range of injection pressure was 40~160MPa, which was commonly used in high pressure common rail diesel engine under middle and high loads. The experiments were conducted by using a highspeed photography technology and a combustion pressure acquisition system. The soot formation characteristic was studied by natural flame luminosity. Results show that, keeping injection pulse width or fuel injection volume the same, the test results have the same change trend: with the increase of injection pressure, the flame luminosity becomes weaker; the ignition region becomes larger; and the flame liftoff length becomes longer. In addition, the combustion pressure rise rate would increase. Also, the moment that pressure begins to rise and the moment that the maximum combustion pressure occurs are both advanced. At the same time, the heat release rate reaches peak more quickly and the peak value increases gradually. Keeping the volume of injected fuel unchanged, with the increase of injection pressure from 80MPa to 160MPa, the ignition delay is shortened from 1.7ms to 1.4ms; the combustion duration is shortened from 6.9ms to 4.7ms; and the soot formation is reduced significantly. However, such trend is weakened with the increase of the injection pressure.