Spark ignition studies in flowing liquid fuel-air mixtures

The thesis describes a programme of research to determine ignition energy requirements in flowing kerosene spray air mixtures under various flow conditions such as velocity, mixture strength, spray mean drop size and drop distribution.

In order to determine the spray characteristics of mixture ratio, mean drop size and drop distribution in the flowing fuel-air spray accurately, new designs have been evolved and employed.

A single rectangular pulse of constant power was employed for initiating ignition in the mixture. The flow parameters were found to have considerable influence on spark characteristics and hence on the energy released in the spark. The breakdown voltage requirements of the spark in the two phase flow differed from they of premixed gaseous mixtures. In the range of weak mixtures investigated, optimum spark duration was found to vary depending on spray drop size between 30 and 60 microseconds. Minimum ignition energy increased with increase in velocity, but decreased with reduction in drop diameter and with increase in equivalence ratio. Low flow number atomisers giving small drop sizes extended the weak ignition limits for a given spark energy. Spray drop size and distribution were found to have a singularly large influence on all aspects of ignition.

The thesis includes a detailed account of the designs and procedures employed in carrying out the investigation, and also a discussion on the significance of the results on the practical aspects of liquid fuel ignition in aero engine combustion system.