In recent years, the environmental impact of aviation engines has been a topic of special interest. Increasing the efficiency of gas turbine engines is a great challenge considering the increasingly restrictive regulations in terms of pollutant emissions. Regarding the restrictions proposed for the next years, not only CO2 or NOx have received serious attention, but also other pollutants as CO, unburned hydrocarbons and soot because of the adverse impacts on health and environment.
The ESTiMatE project, which is part of the Clean Sky program, is focused on the development of advanced soot models to quantify aeroengine particulate emissions. In this context, an adequate prediction of the combustion process is the cornerstone upon which soot predictions will be based. Therefore, ESTiMatE partners also deal with the application of state-of-art combustion models for the prediction of local heat release, temperature and species within the combustion chamber of aeroengines.
As a first step, ESTiMatE researchers at Universitat Politècnica de València (UPV) and Barcelona Supercomputing Center (BSC) are currently testing combustion models when applied to reference spray flames. The selected test case is the so-called Coria-Rouen Spray Burner (CRSB), where a liquid heptane flow of 0.28 g/s is injected through a hollow-cone injector into an air non-swirling coflow of 6 g/s at atmospheric pressure and temperature. Several experimental measurements have been performed for this test case to deliver information on different variables such as local flow and droplet velocity, droplet temperature and OH species distribution [1, 2]. In addition, analysis of flame structure has been carried out in other works with different modelling approaches [2, 3, 4].
Calculations have been carried out with the Alya code developed by BSC, using Large-Eddy Simulations and a combustion model based on the tabulation of diffusion flamelets, an approach that considers that the turbulent flow can be described as an ensemble of laminar one-dimensional flames. Predictions of velocity evolution, local flow velocity and reaction zone location are adequately captured by the model, when compared to experimental measurements.
On the base of model predictions, a detailed analysis of the flame structure has been carried out. This burner shows a double reaction front structure, with an inner partially-premixed flame and an outer diffusion flame. Even though the system works at steady conditions, the turbulent flamefront exhibits transient extinction-reignition events. As already observed in previous experimental works [5], two types of events have been confirmed to describe the extinction phenomena, namely droplet-flame and turbulence-flame interactions and both are well reproduced by simulations. Model predictions give confidence on the accuracy of the combustion approach, which will be later developed within the course of ESTiMatE to include soot models.
Example of CFD model predictions for CRSB. Left: Temperature. Right: velocity.
[1] A. Verdier, J. Marrero Santiago, A. Vandel et al., “Experimental study of local flame structures and fuel droplet properties of a spray jet flame,” Proceedings of the Combustion Institute, vol. 36, no. 2, pp. 2595–2602, 2017.
[2] F. Shum-Kivan et al., “Experimental and numerical analysis of a turbulent spray flame structure”. Proceedings of the Combustion Institute, vol. 36, no. 2, pp. 2567–2575, 2017.
[3] Adrien Chatelier et al., “Large Eddy Simulation of a Turbulent Spray Jet Flame Using Filtered Tabulated Chemistry”. Journal of Combustion, 2020.
[4] Michael Philip Sitte and Epaminondas Mastorakos, “Large Eddy Simulation of a spray jet flame using Doubly Conditional Moment Closure”. Combustion and Flame, vol. 199, pp. 309–323, 2019.
[5] Antoine Verdier, J. Marrero Santiago, A. Vandel et al., “Local extinction mechanisms analysis of spray jet flame using high speed diagnostics”. Combustion and Flame, vol. 193, pp. 440–452, 2018.