Reaction Zone Propagation by Spark Discharge in Homogeneous Lean Charge after Low-Temperature Oxidation 2015-01-0820
The interaction between spark discharge and low-temperature oxidation (LTO) was investigated using an optical compression and expansion machine fueled with n-C7H16 or i-C8H18 for an equivalence ratio of 0.33. Charge pressure was adjusted so that the compression stoke could induce LTO for n-C7H16, but could not lead to high-temperature reactions. A spark was discharged in the field before, during, or after the LTO for n-C7H16 or in the field without LTO for i-C8H18. Reaction zones were induced in the field after the LTO, whereas no reaction zones were induced in the fields before the LTO and without LTO. Local ignitions were induced in the areas surrounding the propagating reaction zones. The reaction zone propagation with the low equivalence ratio must be a different phenomenon from conventional flame propagation. The reaction zones can compress or heat the surrounding areas containing H2O2 and CH2O, and accelerate an H2O2 regeneration loop in the pre-reaction zones. The reaction zone induction and propagation can be supported thermally by the H2O2 regeneration loop or chemically by OH generated from H2O2. The local ignitions also can be induced by the H2O2 regeneration loop in the surrounding areas.
The interaction between flame propagation and LTO also was investigated with an equivalence ratio of 0.52. Flame propagation was induced for both n-C7H16 and i-C8H18. Local ignitions were induced in the end gas for n-C7H16. The flame propagation in the field after the LTO was considerably faster than that in the field without LTO. The flame propagation can be accelerated in the field during the LTO and remarkably in the field after the LTO.