Modelling of Soot Formation in a Kerosene Spray Flame

Abstract

Modelling the formation of soot in a kerosene spray flame is an important consideration in the design and development of gas turbine combustors. The aviation gas turbine engines run on kerosene-type jet fuels. Formation and emission of soot not only pollutes the environment but also augments the radiative heat flux from the flame, which may result in overheated liners and atomizers. Many complex processes are involved in the spray combustion in gas turbine combustors, which include turbulent transport of gas, formation of the fuel spray, droplet motion and evaporation, chemical reaction and thermal radiation in addition to pollutant formation. Each of these requires adequate modelling efforts for the right prediction of the overall process. In this chapter, a modelling technique for the prediction of spray flame and soot formation has been discussed in connection with the kerosene fuel. Considering the computational economy, we have restricted the discussion on RANS-based modelling, which is still popular in the industrial scale for the prediction of combustion phenomenon. Stochastic separated flow model is considered for the two-phase transport of the droplets formed in the atomized spray. The combustion of fuel follows the non-premixed flame mode, which has been modelled using the laminar flamelet model. The soot model is a semi-empirical one for which the model constants have been optimized for kerosene fuel. It is found that the optimized constants work well for kerosene in predicting the soot, which finally leads to good predictions of the liner wall temperature and exit gas temperature from the combustor. Different cases have been run with different air flow split into the combustor to analyse the effects using the developed model.