Numerical investigation of the influence of injection strategies on hydrogen engine performance

Hydrogen is an ideal alternative fuel for internal combustion engines with many advantages, such as high energy density and fast flame speed. In this study, the parameters of the laminar flame speed expression were modified in GT-POWER, and the combustion model was validated by the experimental cylinder pressure and heat release rate under different equivalence ratios. The influence of the injection strategy, including the effects of injection timing and dual injection, on the performance of a hydrogen engine was investigated. The results revealed that an increase in the injection rate and a certain delay at the end of injection (EOI) were beneficial for the improvement of the indicated thermal efficiency (ITE). The later the EOI, the earlier is the ignition timing (IT) of the maximum ITE relative to the EOI. Based on the temporal relationship between IT and injection timing, four types of injection modes—late ignition (LI), tail ignition (TI), center ignition (CI), and head ignition (HI)—were suggested, and a series of performance simulations of the four modes was conducted. When the EOI was at -12°, -6°, 0° and 4° CA (crank angle) ATDC (after top dead center), the ignition mode of the maximum ITE for a single injection was late ignition (LI), tail ignition (TI), center ignition (CI), and head ignition (HI), respectively. The maximum ITE increased with an increase in the secondary injection mass under the dual-injection condition. The injection strategy for the maximum ITE is the TI mode for both single and dual injections.