A DNS study of ignition characteristics of a lean PRF/air mixture with CH2O and H2O2 addition under HCCI combustion-relevant conditions
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- A DNS study of ignition characteristics of a lean PRF/air mixture with CH2O and H2O2 addition under HCCI combustion-relevant conditions
- Kim, Jong Hak; Yu, Gwang Hyeon; Chung, Suk Ho; Yoo, Chun Sang
- Issue Date
- Elsevier BV
- COMBUSTION AND FLAME, v.234, pp.111654
- The effects of additive injection including O and HO on the ignition characteristics of a lean primary reference fuel (PRF)/air mixture under homogeneous-charge compression ignition (HCCI) combustion conditions are investigated using 2-D direct numerical simulations (DNSs) with a 116-species reduced chemical mechanism. The 2-D DNSs of HCCI combustion are performed by varying the type and amount of the additives with a pseudo-species model and a compression-heating/expansion-cooling model. It is found that the first-stage and main ignitions are retarded by O addition while the latter is promoted by HO addition. By adjusting the amounts of dual additives, the main ignition can be manipulated to occur at a specific time similar to that with no additives while its mean heat release rate becomes more distributed over time than that with no additives. Combustion mode analysis reveals that a mixed mode of combustion occurs during the late phase of HCCI combustion with O addition or dual additives, while spontaneous ignition mode of combustion is predominant for cases with HO addition or no additives. Displacement speed analysis also verifies that O addition induces deflagration rather than spontaneous ignition at the reaction fronts, which consequently leads to a smooth ignition of the RPF/air mixture. In addition, chemical explosive mode analysis (CEMA) identifies important variables and elementary reactions for low-, intermediate-, and high-temperature chemistries for the ignition of PRF/air mixture with and without additives.
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