Influence of fuel volatility on combustion and emission characteristics in a gas turbine combustor at different inlet pressures and swirl conditions

Abstract

The practical challenges in research in the field of gas turbine combustion mainly centre around a clean emission, a low liner wall temperature and a desirable exit temperature distribution for turboma-chinery applications, along with fuel economy of the combustion process. An attempt has been made in the present paper to develop a computational model based on stochastic separated flow analysis of typical diffusion-controlled spray combustion of liquid fuel in a gas turbine combustor to study the influence of fuel volatility at different combustor pressures and inlet swirls on combustion and emission characteristics. A κ-ɛ model with wall function treatment for the 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 (PDF) size distribution and a given spray cone angle. A radiation model for the gas phase, based on the first-order moment method, has been adopted in consideration of the gas phase as a grey absorbing-emitting medium. The formation of thermal NO x as a post-combustion reaction process is determined from the Zeldovich mechanism. It has been recognized from the present work that an increase in fuel volatility increases combustion efficiency only at higher pressures. For a given fuel, an increase in combustor pressure, at a constant inlet temperature, always reduces the combustion efficiency, while the influence of inlet swirl is found to decrease the combustion efficiency only at higher pressure. The influence of inlet pressure on pattern factor is contrasting in nature for fuels with lower and higher volatilities. For a higher-volatility fuel, a reduction in inlet pressure decreases the value of the pattern factor, while the trend is exactly the opposite in the case of fuels with lower volatilities. The NOx emission level increases with decrease in fuel volatility at all combustor pressures and inlet swirls. For a given fuel, the NOx emission level decreases with a reduction in combustor pressure and an increase in inlet swirl number.