Ignition Study in a Gas Turbine Combustor

Abstract

Experiments were conducted in a T63 engine combustor to: (I) gain a better understanding of the roles played by fuel properties and atomization in ignition and (2) give experimental verification of assumptions used in ignition models. Ten test fuels were used, some of which were specially blended to vary either viscosity or volatility while holding the other constant. Six atomizers were used to vary the fuel spray characteristics, and average drop sizes, represented by Sauler mean diameter (SMD), were measured. Air temperatures were varied from 239 to 310K. Ignition comparisons were made by the minimum fuel-air ratios required to achieve light-off. Measurements of gas velocity and fuel-air ratio were made at the spark gap. Approximate ignition delay times were determined from high-speed photographs of the ignition process. Significant results for this combustor included: (1) viscosity, which determined atomization characteristics, was more important than volatility in the ignition process, (2) ignition depended more on achieving a critical drop size than on reaching the lean-limit fuel-air ratio. (3) fuel temperature was found to be more important than air temperature for low-temperature ignition, an effect due principally lo viscosity and atomization rather than evaporation. A practical implication is that fuel heating would give a greater improvement in cold-start performance than heating the combustor inlet air.