Effects of biodiesel injector configuration and its injection timing on performance, combustion and emissions characteristics of liquid ammonia dual direct injection engine

Ammonia is a promising carbon-neutral fuel that can be stored and transported in liquid form, offering a viable alternative to diesel fuel. In addition, it can be used directly in diesel engine in its liquid form in dual fuel mode. Hence, a single-cylinder diesel engine was modified to implement two common rail (CR) injection systems, allowing the direct injection of liquid ammonia with biodiesel. As biodiesel was used for a pilot fuel with lower injected mass, this study aims to investigate the influence of the number of nozzles in the biodiesel injector on the performance, combustion, and emissions characteristics of the liquid ammonia-biodiesel dual direct injection engine. Therefore, the number of holes in the CR injector was closed in various configurations to improve injection parameters. Furthermore, various biodiesel start of injection (SOI) timings were tested, ranging from −24 to −14 CAD, while the SOI of ammonia was kept at −10 CAD with an ammonia mass ratio of 67.2%. The results showed that welding three nozzles from the original six-nozzle injector resulted in a remarkable 29.2% reduction in NH₃ and CO emissions. Furthermore, the highest indicated thermal efficiency of 39.7% was obtained for the injector with 3b nozzles. Additionally, late injection of both fuels led to an increase in particulate matter emissions, from 10.5 to 15.2 mg/m³, due to the formation of fuel-rich zones at high temperatures. However, it reduced NOx and CO emissions by 1.4 and 4.4 g/kWh, respectively, compared to the early SOI of biodiesel. Moreover, the lowest N2O emission was measured at 115.0 ppm in the earliest SOI of biodiesel at −24 CAD.