Influence of fuel volatility and spray parameters on combustion characteristics and NO x emission in a gas turbine combustor

Abstract

The main thrust in research in the field of gas turbine combustion centers around a clean emission, a low liner wall temperature, a desirable exit temperature distribution for turbo-machinery applications along with a fuel economy of the combustion process. An attempt to meet the challenge has been made in the present paper in developing a computational model based on stochastic separated flow analysis of a typical diffusion controlled spray combustion of liquid fuel in a gas turbine combustor to study the influences of fuel volatility and different spray parameters on combustion and emission characteristics. A κ– ε model with wall function treatment for near wall region has been adopted for the solution of conservation equations in gas phase. The initial spray parameters are specified by a suitable probability distribution function size distribution and a given spray cone angle. A radiation model for the gas phase, based on first order moment method, has been adopted in consideration of the gas phase as a gray absorbing–emitting medium. Formation of thermal NO x as a post-combustion reaction process, is determined from Zeldovich mechanism. It is recognized that the combustion efficiency is reduced drastically with a decrease in fuel volatilities at lower spray cone angle. For a given fuel, there is a significant reduction in combustion efficiency at a lower spray cone angle and lower initial SMD. The pattern factor of exit temperature distribution is reduced with a decrease in initial SMD, for all fuels. The influence of spray cone angle on pattern factor is contrasting in nature for fuels with higher and lower volatilities. The pattern factor decreases with an increase in spray cone angle for a higher volatile fuel, whereas, the reverse happens in case of lower volatile fuels. It is found that the bulk exit NO x increases with a decrease in fuel volatility for any given set of values of spray parameters. An increase in spray cone angle increases bulk exit NO x especially for lower volatile fuels, and an increase in initial SMD increases the bulk exit NO x for lower volatile fuels only.