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.
