Experimental Investigation of the Matching Boundary and Optimization Strategy of a Variable Geometry Turbocharged Direct-Injected Hydrogen Engine

With the higher demand for torque, power, brake thermal efficiency (BTE), and low NOx emissions of hydrogen engines, direct injection and turbocharging are the most effective methods to improve performance. However, due to the large air flow rate variation range with lean combustion and low exhaust gas energy, the turbine needs to be adjusted significantly, and the performance of the conventional waste gate turbochargers is limited. In this study, a 2.0 L direct-injected turbocharged hydrogen engine was studied experimentally and matched with a variable geometry turbocharger (VGT). The working boundary of the VGT determined by abnormal combustion and exhaust back pressure is proposed at all working conditions as it changes from 10-50 % @1500 rpm to 40-75 % @4500 rpm. Control of the VGT to balance combustion and gas exchange was achieved to reach the highest BTE of 42.57 %. Further, high torque of 326 Nm and high power of 125 kW are explored and different VGT opening strategies are compared. An optimized VGT opening control strategy is proposed, which is divided into five regions at different loads to ensure best performance. The VGT opening control strategy based on lambda control and the trade-off between combustion and gas exchange efficiency at all working conditions can be valuable in the development of high-performance hydrogen engines.