The heating, evaporation and combustion of kerosene droplets in a gas-turbine combustor: CFD modelling using the discrete component approach

The modelling of heating, evaporation and combustion processes in a combustion system is crucial to its design and advancement [1,2], and essential to the assessment of the suitability of kerosene as an aviation fuel [3]. In this study, we have conducted a detailed analysis of kerosene fuel droplet heating and evaporation, using the previously developed discrete component model (DCM). Kerosene fuel composition (approximated by 44 components of the full composition reported in [4]) is replaced with 2 surrogate components to reduce the computational time. In contrast to the classical industrial analyses of aviation fuel (e.g. the distillation curve method [5]), the DCM takes into account gradients of species mass fractions in droplets. It is based on the analytical solutions to the heat transfer and species diffusion equations subject to appropriate boundary and initial conditions [6]. Numerical codes using these solutions were extensively verified and validated in [7–9]. The effective thermal conductivity and effective diffusivity approaches for moving droplets are used in the model. The DCM was implemented in the commercial CFD software of ANSYS-Fluent which was applied to study the processes in a combustor. A polyhedral mesh was used for the hydrodynamic model. This opened opportunities for the simulation of the full combustion cycle. The influence of droplet evaporation on the combustion process was investigated. The analysis was applied to a balanced mixture of kerosene and diesel fuels, represented in the ANSYS-Fluent database by C12H23 and C10H22, respectively. The initial droplet diameter and temperature were 100 µm and 375 K, respectively. The ambient gas temperature and pressure were 800 K and 4 bar, respectively. A co-axial air-blast atomizer was used with air and fuel mass flowrates of 0.175 kg/s and 0.003 kg/s, respectively, and an injection speed of 1 m/s. The evolution of droplet radii with time was predicted using three approaches, namely: 1) the results predicted by standard ANSYS Fluent software using constant properties; 2) the results predicted by ANSYS Fluent with the implementation of transient properties of fuel composition using the user defined function (udf), but without the DCM; and 3) ANSYS Fluent results with full implementation of the DCM and transient thermodynamic and transport properties. The preliminary results show that the maximal impact of incorporating the DCM into the ANSYS-Fluent prediction of droplet evaporation is up to 10.4% compared to the case when a standard ANSYS-Fluent model is used. Also, our results indicate that the fuel composition and temperature gradient inside droplets, which are ignored in the standard ANSYS Fluent model, can lead to noticeable impact on the spray formation and combustion processes. The new results have been compared with those reported in the literature [12] for kerosene droplets of 1.8 mm initial diameter. General agreement between the numerical results and experimental data was found. In our analyses, we considered the impact of thermal-swelling on droplet evaporation. Finally, the combustion of the blended fuel droplets was simulated, and the influence of fuel evaporation and species diffusion on flame properties was investigated and will be presented in the full paper. References [1] Al Qubeissi, M., 2018, “Predictions of Droplet Heating and Evaporation: An Application to Biodiesel, Diesel, Gasoline and Blended Fuels,” Applied Thermal Engineering, 136(C), pp. 260–267. [2] Sazhin, S. S., 2014, Droplets and Sprays, Springer, London. [3] Jones, E. G., and Balster, L. M., 1997, “Impact of Additives on the Autoxidation of a Thermally Stable Aviation Fuel,” Energy & Fuels, 11(3), pp. 610–614. [4] Lissitsyna, K., Huertas, S., Quintero, L. C., and Polo, L. M., 2014, “PIONA Analysis of Kerosene by Comprehensive Two-Dimensional Gas Chromatography Coupled to Time of Flight Mass Spectrometry,” Fuel, 116, pp. 716–722. [5] Lovestead, T. M., and Bruno, T. J., 2009, “Application of the Advanced Distillation Curve Method to the Aviation Fuel Avgas 100LL,” Energy & Fuels, 23(4), pp. 2176–2183. [6] Sazhin, S. S., 2017, “Modelling of Fuel Droplet Heating and Evaporation: Recent Results and Unsolved Problems,” Fuel, 196, pp. 69–101. [7] Al Qubeissi, M., Al-Esawi, N., Sazhin, S. S., and Ghaleeh, M., 2018, “Ethanol/Gasoline Droplet Heating and Evaporation: Effects of Fuel Blends and Ambient Conditions,” Energy & Fuels, 32(6), pp. 6498–6506. [8] Sazhin, S. S., Elwardany, A. E., Krutitskii, P. A., Deprédurand, V., Castanet, G., Lemoine, F., Sazhina, E. M., and Heikal, M. R., 2011, “Multi-Component Droplet Heating and Evaporation: Numerical Simulation versus Experimental Data,” International Journal of Thermal Sciences, 50(7), pp. 1164–1180. [9] Elwardany, A. E., Sazhin, S. S., and Im, H. G., 2016, “A New Formulation of Physical Surrogates of FACE A Gasoline Fuel Based on Heating and Evaporation Characteristics,” Fuel, 176, pp. 56–62. [10] Al Qubeissi, M., 2015, Heating and Evaporation of Multi-Component Fuel Droplets, WiSa, Stuttgart. [11] Sazhin, S. S., Al Qubeissi, M., Kolodnytska, R., Elwardany, A. E., Nasiri, R., and Heikal, M. R., 2014, “Modelling of Biodiesel Fuel Droplet Heating and Evaporation,” Fuel, 115, pp. 559–572. [12] Wang, F., Liu, R., Li, M., Yao, J., and Jin, J., 2018, “Kerosene Evaporation Rate in High Temperature Air Stationary and Convective Environment,” Fuel, 211, pp. 582–590.