Performance and emissions of a direct-injection engine fueled with natural gas/hydrogen blends

An experimental study was conducted on performance and emissions of a direct-injection spark ignited engine fueled with natural gas /hydrogen blends. The results show that for a fixed fuel injection duration, the brake mean effective pressure and effective thermal efficiency would decrease with the addition of hydrogen in natural gas when hydrogen addition fraction is small and would increase with the increase of hydrogen fraction in natural gas when hydrogen fraction reaches up to 5 percent to 10 percent. This phenomenon is more obvious in the case of lean combustion, indicating a strong influence of hydrogen addition on lean mixture combustion. The exhaust HC and CO₂ decreased with the increase of hydrogen fraction in natural gas, and this would be due to the increase in H/C ratio and excessive air ratio. Under the circumstance of lean mixture combustion, exhaust NO_x decreased slightly with the increase of hydrogen addition while exhaust CO had little variation with hydrogen addition.