Some opertaing characteristics of novel ignition devices for hydrocarbon/air mixtures

Thesis

An introduction to the problems of ignition in the petrol and gas turbine engine is given. Two new ignition devices are considered for their suitability to overcome these problems and a series of experiments were performed to evaluate their relative merits.

The use of a laser spark and the development of a plasma plug igniter were compared with sparks of variable energy produced between two electrodes. A simple combustion chamber was used for the experiments and ionisation probes were used to follow the propagation of the flame from the ignition source and through the gaseous mixtures. The conditions of the experiments were as follows:

Pre-mixed methane/air of 1.0, 0.8 and 0.6 stoichiometry
Pressures	101 kN/m2 - 1067 kN/m2
Laser spark energies	30 mJ - 400 mJ
Plasma plug energies	50 mJ - 1500 mJ
Electrode spark energies	10 mJ - 2500 mJ

Samples of the combustion products were taken and the results for the three mixture ratios are presented. The performances of the three ignition methods are presented by plotting the flame speeds observed from the ignition sources as functions of energy.

Practical considerations eliminate the use of the laser as an ignition method but the plasma plug could be used for automotive applications if some control of the energy was exercised. The gas turbine engine appears to be the roost likely application of the plasma plug as it offers greater penetration into the combustion chamber than current surface discharge igniters.

Authors: Waterson, K

• DOI: 10.5287/ora-ppo9gopk9
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford