Effects of direct water injection on engine performance in engine fueled with hydrogen at varied excess air ratios and spark timing

In this paper, the effects of direct water injection (WI) on characteristics of combustion and emissions for a hydrogen (H2)-fueled spark ignition (SI) engine were experimentally investigated. The experiments were conducted under different excess air ratios (λ) and ignition timing (IT). In each test, the water to air ratio (α) was varied, and the results were compared with baseline data without WI. The experimental results showed that in-cylinder pressure decreased, indicated thermal efficiency increased, and the flame development and propagation periods prolonged when WI was used. When α increased to 1.87%, NOx emissions expelled from the original engine separately decreased by 36.9% and 55.4% when IT were 5°CA BTDC and 15°CA BTDC at λ of 1.15.