ABSTRACT
In the present study, the effect of ambient density () on spray two-stage auto-ignition characteristics under cold-start condition was investigated using both optical and numerical methods. By the high-speed Shadowgraph, the LTI (low-temperature ignition delay) and HTI (high-temperature ignition delay) were obtained and followed an increasing trend with the decreasing
. Both experimental and simulated results show that HTI is more sensitive to the
than LTI, because the high-temperature chemistry is more suppressed at higher
due to the increased scalar dissipation rate . Moreover, the simulation showed that the high-temperature ignition emerges at the same mixture fraction of 0.065, regardless of changes of
, which indicates that
has little effect on the ignition site in the mixture fraction space. Further kinetic analysis found that as the
decreases, the O2 concentration reduces and the reaction rates of both low- and high-temperature reactions reduce, leading to the increased LTI and HTI. When the HTI increases to such a long time that no ignitable mixture exists in the space due to the continuing diffusion after the end of injection, the spray misfire happens.
Acknowledgments
This study is based upon work supported by National Natural Science Foundation of China [Grant No.:51976011] and China Postdoctoral Science Foundation (Grant No.: 2020M680378).
Disclosure statement
No potential conflict of interest was reported by the author(s).