Development and experimental validation of a novel twin injector concept for a biogas diesel RCCI engine

A bi-fuel RCCI engine that uses a low reactivity renewable fuel like biogas along with diesel can decrease the NOx emissions and at the same time operate with high efficiency. Generally, diesel is injected in pulses, one very early and the other close to TDC. The early injection if done with conventional wide angle diesel injectors leads to wall wetting resulting in high THC, CO and adversely affects the efficiency. In this work a combination of injectors, one with a narrow angle between the sprays and the other with a wide angle between the sprays (NW Injectors) was evaluated for early and near TDC injections respectively in a biogas diesel RCCI engine. Simulations with a validated CFD model were used to determine the suitable injection parameters including the orientation of the spray holes, number of holes of the Narrow angle Injector (NI), fuel split ratio between narrow and wide injectors, injection timing and injection pressure. The studies indicated that the NI sprays have to hit the periphery of the piston bowl for good mixture preparation. The 3-hole NI configuration with the sprays aimed at the periphery of the piston bowl resulted in minimum fuel deposition, highest efficiency, and lowest soot and HC emissions. The NI was subsequently manufactured, installed on the engine and experiments were conducted in the biogas diesel NW RCCI mode for determining the performance and emissions and for comparing the same with the single Wide angle Injector RCCI (WI RCCI) mode in order to bring out its potential.