Effect of nitric oxide on the performance and emissions of a hydrogen-fueled HCCI engine

Homogeneous charge compression ignition (HCCI) engines have historically generated interest due to its po-tential to achieve high efficiency and low emissions. This paper presents an experimental investigation of hydrogen port fuel injection in a modified Cooperative Fuel Research (CFR) engine operated under HCCI con-ditions. The effect of adding nitric oxide (NO) to the intake air on engine performance, emissions, and com-bustion characteristics was investigated at various inlet temperatures. The experiments considered the operating regime and limitations for hydrogen HCCI engines with and without NO addition. The engine can operate over a wide range of air-fuel ratios i.e., lambda = 2.7 to 4.0 at 150 OC inlet air temperature without NO addition. NO also acts as a knock promoter in reciprocating engines, limiting the engine's output. The results indicate that adding NO significantly promotes the auto-ignition of the hydrogen-air mixture, thereby extending the engine's operable range, and an ultra-lean lambda of 5.0 can be reached. Our findings indicate that NO has the most notable effect on engine performance at an inlet air temperature of 90 OC. Furthermore, the results show that the addition of NO increases the amount of NOx emissions in the exhaust gas; about 50 ppm of NO was converted into NO2 during the combustion process. Adding NO to the hydrogen-air mixture has the potential to extend the engine's range of operation in HCCI providing a promising avenue for further research into HCCI combustion engines and the potential to improve efficiency.