Influences of various turbocharging systems combined with Miller cycle on performance, combustion, and emissions of a heavy-duty diesel engine at high altitude

High-altitude regions are widespread globally, and the low air density at such elevations imposes significant challenges on diesel engine performance. Combining the Miller cycle with advanced turbocharging technology can effectively improve the performance and emissions of diesel engines in such environments. However, limited research has explored the effects of various turbocharging schemes on the performance of Miller cycle diesel engines in high-altitude environments. To address this gap, this research examines a heavy-duty diesel engine using both one- and three-dimensional simulation models. Three turbocharging systems, namely waste-gated turbocharger (WGT), variable geometry turbocharger (VGT), and two-stage turbocharger (TST), are examined in conjunction with two Miller timings: early intake valve closing (EIVC) and late intake valve closing (LIVC), at 2000 m above sea level. Their impacts on engine torque output, fuel consumption, combustion characteristics, and emission performance are comprehensively evaluated. Results indicate that the two-stage turbocharged engine achieves the highest torque and lowest fuel consumption, followed by the VGT, while the WGT demonstrates the weakest performance. The EIVC delivers superior torque and fuel economy compared to LIVC. Moreover, employing an advanced turbocharging system combined with appropriately Miller timing markedly improves the in-cylinder fuel-air mixture and combustion temperature distribution in plateau region. This effectively suppresses NOx formation and reduces soot emission. These findings highlight the Miller cycle, combined with advanced turbocharging technology, as a promising solution for restoring diesel engine performance and reducing emissions at high altitudes.