Parallel perturbation analysis of combustion cycle-to-cycle variations and emissions characteristics in a natural gas spark ignition engine with comparison to consecutive cycle method.

Severe combustion cycle-to-cycle variations (CCVs) in spark ignition (SI) engines significantly increase partial or incomplete combustion cycles, which may result in combustion instability or even misfire under extreme conditions, thereby seriously affecting the engine performance and increasing the unburned hydrocarbon and carbon monoxide emissions. In this study, the consecutive cycle method (CCM) and parallel perturbation method (PPM) are utilized to simulate the CCVs in a natural-gas (NG) SI engine. Specifically, 25 consecutive and concurrent cycles of the SI engine are simulated, and simulation results are compared with the experimental data.

Unraveling the geometry dependence of in-nozzle cavitation in high-pressure injectors.

Cavitation is an intricate multiphase phenomenon that interplays with turbulence in fluid flows. It exhibits clear duality in characteristics, being both destructive and beneficial in our daily lives and industrial processes. Despite the multitude of occurrences of this phenomenon, highly dynamic and multiphase cavitating flows have not been fundamentally well understood in guiding the effort to harness the transient and localized power generated by this process.

Interaction between supersonic disintegrating liquid jets and their shock waves.

We used ultrafast x radiography and developed a novel multiphase numerical simulation to reveal the origin and the unique dynamics of the liquid-jet-generated shock waves and their interactions with the jets. Liquid-jet-generated shock waves are transiently correlated to the structural evolution of the disintegrating jets. The multiphase simulation revealed that the aerodynamic interaction between the liquid jet and the shock waves results in an intriguing ambient gas distribution in the vicinity of the shock front, as validated by the ultrafast x-radiography measurements.