Ignition delays of alkanes and other hydrocarbons

In a shock tube there is a clearly defined initiation of reaction (t = 0) at passage of the incident or reflected shock through the reactant mixture. Very wide ranges of pressure, temperature and composition are also accessible, but measurements of ignition delay in mixtures at temperatures below 1000 K are not without difficulty, as discussed in Section 6.3.4 [29]. Data obtained from shock tubes generally pertain to shocked gas temperatures in excess of 1500 K [89,90]. 

If ignition delays measured in different devices under the same conditions are brought together it becomes clear that there are incompatibilities that cannot be attributed to differences in composition or pressure. In rapid compression machines the discrepancies between different sets of results may arise from different rates of compression [142], which can affect the rate of heat transfer in the early stage of the post-compression interval as a result of the extent of gas motion that is created by the piston motion [50,102]. Ignition delays become longer as the heat loss rates are 

The light emission and pressure traces give clear indication of cool-flame phenomena, characterized by a relatively small pressure rise and 

Cadman [145] studied ignition delays of toluene behind a reflected shock in the shocked gas temperature range above 1000 K (Fig. 6.22). Liquid fuel droplets were injected into the shock tube in these experiments. It is likely that their complete evaporation occurred during the interval between passage of the incident and reflected shocks. 

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