Hydrogen Injection Position Impact: Experimental Analysis of Central Direct Injection and Side Direct Injection in Engines

A detailed investigation was carried out on the performance, combustion, and emissions of a single-cylinder direct injection hydrogen spark ignition (SI) engine with either a side-mounted direct injection (SDI) or a centrally installed direct injection (CDI) injector. The first part of the study analyzed the performance and emissions characteristics of CDI and SDI engine operations with different injection timings and pressures. This was followed by comparing the engine’s performance and emissions of the CDI and SDI operations at different engine speeds and relative air-to-fuel ratios (lambda) with the optimized injection pressure and timings. Furthermore, the performance and emission attributes of the hydrogen engine with the CDI and SDI setups were conducted at a fixed λ value of 2.75 across a broad spectrum of engine loads. The study’s main outcome demonstrates that both direct injection systems produced near-zero CO2, CO, and HC emissions. Stable engine operations could be achieved over a wide range of air-to-fuel ratios by the CDI and SDI setups, though the CDI enabled a wider range from stoichiometric to lambda = 3.8. The CDI system also offered noticeably higher thermal efficiencies than the SDI engine. The study also illustrated the sensitivity of each injection system to the variation of the injection pressure and timing and identified the optimum operation settings for each system. Finally, the study indicates that the emissions characteristics of CDI and SDI are similar at low and mid-load, although SDI resulted in both higher NOx and hydrogen emissions than CDI.