Development of a 6.7L Direct Injection, Lean Burn H2 Spark Ignition Engine for Medium- and Heavy-Duty Commercial Vehicles

This work is part of a production-intent program at Cummins to develop a 6.7L direct injection (DI), lean burn H2 spark ignition (SI) engine for medium- and heavy-duty commercial vehicles that are intended to be compliant with global VII criteria pollutants emissions standards. The engine features a low-pressure DI fuel injection system, a tumble-based combustion system with a pent-roof combustion chamber, two-stage boosting system without EGR, and dual overhead cams (DOHC) with cam phasers. The paper focuses primarily on the performance system architecture development encompassing combustion system, air-handling system, and valve strategy. Comprehensive 3D-CFD guided design analysis has been conducted to define the tumble ports, injection spray pattern, and injection strategy to optimize charge homogeneity and turbulence kinetic energy (TKE). In addition, the boosting system architecture and the valve strategy have been thoroughly evaluated through 1-D system-level engine cycle analysis. Steady-state test results showed that the engine produces >40% BTE over a wide range of engine speed and load while achieving the targeted torque and power. The use of a well-matched, two-stage boosting system produces λ >2.0 across the full engine operating map, thereby leading to low engine-out NOx emissions when combined with the tailor-designed combustion system. Moreover, the engine system demonstrated robust performance over WHTC test cycle.