Hydrogen is an ideal engine fuel. Pure hydrogen engines do not produce CO and HC emissions but face the high NOx emission problem. Inner-engine control and outer-engine control are two ways to decrease the NOx emission. Outer-engine control mainly reduce NOx emission through selective catalytic reduction (SCR), which has been well studied. However, there are few studies on NOx emission control of pure hydrogen engines through inner-engine control. In this paper, the closed homogeneous reactor (CHR) in Chemkin Pro was used to simulate the main inner-engine NOx emission control in pure hydrogen engines. The results show that single exhaust gas recirculation (EGR) decreases NOxemission by 45.3% at an EGR ratio of 20%, indicating that the NOx emission is not significantly reduced. However, EGR plus lean-burn decreases NOx emission by 96.31% at a λ of 1.4 and an EGR ratio of 20%, achieving ultra-low NOx emission of pure hydrogen engines. Compared with single EGR and EGR plus lean-burn, SNCR are better for NOx emission control. A NH3 ratio of only 10% can decrease NOx emission by 96.32% on pure hydrogen engines, while a NH3 ratio of 15% can achieve zero NOxemission on pure hydrogen engines without a large λ value and EGR ratio. However, it is necessary to accurately control the NH3 ratio in the cylinder, otherwise it is easy to produce residual NH3 which can pollute the environment.
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