Optimal control strategy of the turbocharged direct-injection hydrogen engine to achieve near-zero emissions with large power and high brake thermal efficiency

Hydrogen, as a clean and sustainable energy source, is an ideal alternative fuel for internal combustion engines. In the process of utilizing hydrogen, the direct-injection (DI) hydrogen engine has been proved to generated large power with high thermal efficiency and a low risk of causing abnormal combustion. However, the emission of nitrogen oxidizer (NOx) remains at a high level in DI hydrogen engines at high loads. Several studies have targeted reducing NOx emissions based on naturally aspirated or supercharged engines with medium power and efficiency. In contrast, the present study focuses on a 2.0 L turbocharged direct-injection engine, achieving large power, high thermal efficiency, and near-zero emissions (below 20 ppm without any posttreatment equipment) simultaneously. The impacts of two effective methods, lean combustion, and retarded ignition are investigated, compared, and combined. An optimal control strategy is proposed and validated under all working conditions from 1000 rpm to 3500 rpm to deal with the trade-off among the power, efficiency, and emissions. The results indicate that lean combustion can rapidly decrease the NOx emission from 2500 ppm to approximately 100 ppm by reducing the cylinder temperature, avoiding the formation of thermal NOx. On this basis, retarded ignition effectively reduces remaining emissions to near-zero with only a 2.5% power loss, whereas lean combustion achieves the maximum brake thermal efficiency (BTE). After optimization, a maximum torque of 221 Nm @ 2500 rpm, 73 kW @ 3500 rpm, and 41.2% BTE @ 2000 rpm and 2500 rpm can be achieved by the turbocharged direct-injection hydrogen engine with near-zero emission.