预喷射策略对氨/柴油双燃料发动机低负荷燃烧和排放特性影响的试验研究

With the rise of the carbon neutrality concept, carbon-free fuel ammonia has attracted extensive attention from internal combustion engine researchers. The ammonia/diesel dual fuel engine can effectively overcome the ignition difficulty of ammonia on the engine and is an effective measure to reduce carbon emissions. Based on a single-cylinder diesel engine, diesel-ignited ammonia combustion experiments were conducted under conditions of 1200 r•min-1 and 30% engine load to systematically study the influence of ammonia premixed ratio, pilot injection ratio and pilot injection timing on the combustion process, performance and emission characteristics of the ammonia/diesel dual fuel engine. The study find that the pilot injection strategy can increase the upper limit of ammonia premixing ratio, reduce the cyclic coefficient of variation and change the heat release rate from single-stage high temperature heat release (HTHR) to two-stage HTHR. With the increase of ammonia premixing ratio, both NOx emissions of the two injection strategies decrease while CO emissions increase. The reduction of NOx emissions may be due to the decrease in in-cylinder temperature, resulting in a reduction in the formation of thermo NOx and fuel NOx. At a 35% ammonia premixed ratio, the effect of pilot injection ratio was studied. With the increase of pilot injection ratio, indicated mean effective pressure (IMEP) first increases and then decreases, while the effective expansion ratio (EER) continues to increase. Medium-low pilot injection ratios can improve the IMEP of the engine, which is because when the pilot injection ratio exceeds 35%, the increase rate in effective expansion efficiency (EEE) is lower than the increase rate in heat transfer loss. When the pilot injection ratio is 35%, the highest IMEP is achieved, CO and NOx emissions are reduced by 23% and 20%, respectively, compared to the single injection strategy. The study on pilot injection timing shows that smaller injection intervals can increase the IMEP of the ammonia/diesel dual fuel engine while reducing CO and NOx emissions.