The experimental investigation on the impact of toluene addition on low-temperature ignition characteristics of diesel spray

Low temperature reaction process becomes more important for auto-ignition diesel spray with ambient temperature reducing. In order to reveal the effects of negative temperature coefficient (NTC), toluene was added to diesel with different ratios due to its non-NTC feature during investigating ignition and combustion characteristics of spray on an optical constant volume combustion chamber. In the experiments, the Mie-scattering and shadowgraph methods were applied to record macroscopic characteristics of liquid-phase and vapor-phase while the high-speed direct shooting was used to record the ignition process of sprays under low ambient temperature regions covers from 663 K to 813 K. The results showed that with the addition of toluene the air-fuel mixing was enhanced obviously but the evaporation of diesel-related components might be inhibited due to the competition between toluene and diesel fuel. Thus, toluene delays the ignition of blends greatly in spite of better air-fuel mixing, and suppresses the NTC behavior at low temperatures regions. It was also observed the blue flame, typically indicates the low temperature reactions, is more difficult to turn into hot flame, indicates the high temperature reactions, as the toluene blend ratio increasing.