Ignition and propagation of a reaction front in a counterflow system of an iso-octane/air stream mixing with an exhaust gas stream is computationally investigated to understand the fundamental characteristics of homogeneous charge compression ignition (HCCI) auto-ignition. Various mixing rates are imposed on the system and the effects of dissipation rates on auto-ignition are studied. Ignition delay and front propagation speed across the mixing layer are determined as a function of a local mixture fraction variable. The results show that mixture inhomogeneity and dissipation rate have a significant influence on ignition. Diffusive transport is found to either hamper or advance ignition depending on the initial reactivity of the mixture. Based on the relative importance of diffusion on ignition front propagation, two distinct ignition regimes are identified: the spontaneous ignition regime and the diffusion-controlled regime. The transition between these two regimes is identified using a criterion based on the ratio of the timescales of auto-ignition and diffusion. The results show that ignition in the spontaneous regime is more likely under typical HCCI operating conditions with iso-octane due to its high reactivity. The present analysis provides a means to develop an improved modelling strategy for large-scale engine simulations.
Bibliographical noteFunding Information:
This work has been sponsored by the Consortium on Homogeneous Charge Compression Ignition Engine Research, directed by the University of Michigan, and funded by the Department of Energy under agreement DE-FC04-01AL67611. The authors would like to thank Professor Tae-Kyun Oh of Dongyang Technical College, Seoul, Korea, for his contribution to the numerical calculation and analysis during the initial phase of the study.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Modeling and Simulation
- Fuel Technology
- Energy Engineering and Power Technology
- Physics and Astronomy(all)