Characteristics and effect factors of pressure oscillation in multi-injection DI diesel engine at high-load conditions

The in-cylinder pressure oscillation during combustion process in multi-injection (MI) DI diesel engine is researched in this paper. The in-cylinder pressure testing is conducted under different operating conditions and different injection parameters. The high-frequency pressure oscillation signal and the oscillation energy are extracted from the in-cylinder pressure signal. The time-frequency characteristics of the pressure oscillation in each combustion stage are analyzed using AGST. The effects of engine speed, load and injection parameters on pressure oscillation are investigated. Results show that for DI diesel engine with pilot-main injection strategy, the amplitude of pressure oscillation in pilot injection combustion (PIC) is the maximum and the oscillation energy in PIC is pretty high. Moreover, the pilot injection also shows important influences on pressure oscillation in main injection combustion. Generally, high engine speed and high load lead to drastic pressure oscillation. However, the pressure oscillation decreases when the engine speed rises above 2200 r/min due to the influence of injection parameters. Under the same engine speed and load, the main injection advance angle and the pilot injection interval time show great influences on the amplitude, oscillation energy and time-frequency characteristics of pressure oscillation in each combustion stage, while the pilot injection quantity has less effects on the pressure oscillation when it varies in a narrow range. Based on the conclusions above, the potential methods to reduce the pressure oscillation are also discussed.