Investigation of Gas Exchange Process on a Highly-Intensified Single Cylinder Diesel Engine with Late Intake Valve Closing Miller Cycle

Abstract

Late intake valve closing (LIVC) Miller cycle was used on a highly-intensified single cylinder diesel engine to reduce the maximum combustion pressure and temperature. Three intake cams with three LIVC timings were designed and tested on the engine bench. The gas exchange process of the Miller cycle was investigated by a 1-D simulation model which was calibrated by experimental data. The analysis was conducted at a constant speed of 3600 r/min and two IMEP loads of 25 bar and 15 bar respectively. Miller depth is named to reflect the retard degree of the LIVC timing. The analysis results show that as the LIVC Miller depth increases, the intake pressure is considerably increased in order to keep the same load. This causes an increase in intake boost work. In addition, the averaged intake pressure difference during the period of BDC-IVC is negative and increases with the retard of IVC timing, resulting in more backflow with the LIVC timing. The backflow rate quickly increases from nearly zero at the original IVC timing of 70°CA ABDC to 22% at the deepest LIVC timing of 120°CA ABDC. Furthermore, the charging efficiency and pumping loss reduce with the retard of IVC timing. The Miller loss is obviously increased at deeper LIVC Miller cycle. On the other hand, the exhaust energy slightly decreases with the retard of IVC timing in this study case, but the ratio of the boost work over the exhaust energy increase considerably with the retard of IVC timing.