Shot-to-Shot Deviation of a Common Rail Injection System Operating with Cooking-Oil-Residue Biodiesel

The shot-to-shot variations in common rail injection systems are primarily caused by pressure wave oscillations in the rail, pipes, and injector body. These oscillations are influenced by fuel physical properties, injector needle movement, and pressure and suction control valve activations. The pressure waves are generated by pump actuation and injector needle movement, and their frequency and amplitude are determined by fluid properties and flow path geometry. These variations can result in cycle-to-cycle engine fluctuations. In multi-injection and split-injection strategies, the pressure oscillation from the first shot can impact the hydraulic characteristics of subsequent shots, resulting in variations in injection rate and amount. This is particularly significant when using alternative fuels such as biodiesel, which aim to reduce emissions while maintaining fuel atomization quality. This study examines the shot-to-shot variations in a second-generation common rail system using cooking-oil-residue biodiesel. The results demonstrate that biodiesel properties impact pressure wave oscillation, shot-to-shot variation, and total injection rate. The study also finds that dwell time has a significant effect on the hydraulic characteristics of the second shot, with minimal influence up to a certain value. However, beyond a certain dwell time value (e.g., 0.8 ms in this study), the impact of dwell time on the pressure fluctuation generated by the second shot is limited. Conducting further research could help deepen our understanding of the influence of shot-to-shot deviations. This could involve exploring biodiesel spray characteristics using techniques such as shadowgraph imaging and studying the effect of these deviations on flame propagation and emission formation. Examining engine performance could also provide valuable insights into the effectiveness of the split-injection strategy and biodiesel blends. Additionally, characterizing biodiesel spray using the double-shot technique to examine spray penetration, cone angle, and/or spray impingement and combustion characteristics could be useful in linking it with the shot-to-shot variation investigated in this study. Such research can contribute to advancing the state-of-the-art knowledge on this topic. © 2023 SAE International.