Reaction Zone Propagation by Spark Discharge in Homogeneous Lean Charge after Low-Temperature Oxidation

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.