A Study on the Effects of EGR and VNT on the Intake and Exhaust Pressure Waves in a High-Pressure Common-Rail Diesel Engine

The transient pressure waves in the intake and exhaust systems directly affect the intake and exhaust processes of diesel engines, thus further affecting the combustion process and the performance of diesel engines. The variation rules of the intake and exhaust pressure waves at different engine speeds and loads in a high-pressure common-rail diesel engine were studied. Then, the effects of EGR rate and VNT nozzle opening on the intake and exhaust pressure waves were systematically studied by bench test and one-dimensional simulation analysis. The results show that at 2000 r·min-1 full-load, when the EGR rate increases from 0 to 10%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms of the intake pressure and the exhaust pressure change significantly. The fluctuation intensity of the intake pressure decreases by 58.6%, and the fluctuation intensity of the exhaust pressure increases by 77.2%. As the EGR rate increases from 10% to 30%, the average intake pressure and the average exhaust pressure both decrease. The fluctuation waveforms are basically unchanged. The increasing magnitudes of the intake and exhaust pressure fluctuation intensities are 16.6% and 20.5%, respectively. As the VNT nozzle opening increases, the average intake pressure and the average exhaust pressure both decrease. The corresponding phases of the intake pressure wave crest and trough are delayed. The fluctuation waveforms of the intake and exhaust pressure are basically unchanged, and the fluctuation intensities do not change significantly.