High Lambda Boosting for Hydrogen Internal Combustion Engine

The commercial vehicle industry continues to move in the direction of lower emissions while reducing its carbon footprint. This study focuses on hydrogen internal combustion engines (H₂-ICE) since it offers a zero-carbon solution to the industry while showing very low NOx emissions when coupled to a conventionally sized aftertreatment SCR system. This work highlights modeling efforts for analyzing key boosting configurations to operate a hydrogen engine at high lambda (relative air–fuel ratio) for lowering NOx, maintain the aftertreatment system reasonable in size, and improving brake thermal efficiency (BTE). GT-Power was used to model H₂-ICE engines from 13L to 19L in displacement with different boosting architectures. Key configurations include a variable geometry turbine (VGT) turbocharger coupled with a supercharger (SC), a VGT with higher engine displacement, and a VGT coupled in series with a fixed geometry turbine (FGT) turbocharger. An exhaustive study comparing these boosting architectures together for steady-state and transient regime performance is the novelty for this study, which is a gap in the existing literatures. Base diesel power curves from both 13L and 15L engines were studied, having maximum brake mean effective pressures (BMEP) from 18 to 21 to 23 bar with λ ≥ 2.2. The VGT+SC was studied with multiple variants including splitting the charge air cooler (CAC) into two parts to provide cooling both pre and post SC, a SC clutch, and a SC bypass. The results show that the VGT (upstream) + SC variant utilizes the SC at low engine speed and high torque, along with all transient regimes from low to high load. The VGT+SC architecture, besides its complexity with clutch and bypass, successfully supports high λ operation (≥2.4), achieving a peak BTE of 43%, and significantly reduces NOx emissions without the need for EGR or large aftertreatment systems. This variant shows the fastest transient response relative to all other configurations in time-to-torque and acceleration cycles while rivaling the highest BTE. VGT+SC can also meet 5500 ft altitude performance with λ ≥ 2.2, leading to low NOx with the same SCR size equivalent to diesel engines and without EGR. Transient response and high BTE are essential to showing that this zero-carbon H₂-ICE solution is viable for the commercial vehicle market.