High-pressure injection or low-pressure injection for a direct injection hydrogen engine?

The study delves into the potential application of the direct injection (DI) hydrogen engine as a carbon-neutral power source, exploring mixing and combustion dynamics across varied injection pressures. This research identifies an optimal injection strategy based on a 3-cylinder 4-stroke cycle turbocharged DI hydrogen engine crucial for enhancing the combustion behavior, significantly influenced by mixture formation. Numerical simulation results for a single cylinder show that rapid flame propagation hinges on a relatively rich mixture surrounding the spark plug. Surprisingly, low-pressure injection demonstrates superior combustion performance under the late-injection strategy, emphasizing the importance of an adjusted nozzle diameter to compensate for reduced flow rates. Furthermore, increasing the nozzle diameter from 0.8 mm to 3.0 mm with an optimal injection timing approaches the same combustion performance under the same injection pressure of 15 MPa. Moreover, low-pressure injection not only augments nozzle sealing and durability but also exhibits promising combustion efficiency and power generation under specific conditions. The study underscores the need for forthcoming research in low-pressure DI hydrogen engines, stressing the significance of high -performance injectors, emission mitigation technologies, and evolved combustion theories.