Abstract
Simulations of a pilot-stabilised flame in a uniformly dispersed ethanol spray are performed using a Doubly Conditional Moment Closure (DCMC) model. The DCMC equation for spray combustion is derived, using the mixture fraction and the reaction progress variable as conditioning variables, including droplet evaporation and differential diffusion terms. A set of closure sub-models is suggested to allow for a first, preliminary application of the DCMC model to the test case presented here. In particular, the DCMC model is used to provide complete closure for the Favre-averaged spray terms in the mean and variance equations of the conditioning variables and the present test case is used to assess the importance of each term. Comparison with experimental data shows a promising overall agreement, whilst differences are related to modelling choices.
Highlights
In a broad range of combustions devices, including most mobile applications such as aeroengines and IC-engines, fuel is supplied in liquid form
The Doubly Conditional Moment Closure (DCMC) model equation for spray flames is derived following the approach by Mortensen and Bilger [12] who used a separated flow model to incorporated the effects of spray evaporation
In this work an emphasis is put on the modelling of the spray combustion and we aim to provide closure for the complete set of evaporation terms that appear in the Favre-averaged transport equations of the conditioning variables
Summary
In a broad range of combustions devices, including most mobile applications such as aeroengines and IC-engines, fuel is supplied in liquid form. Many experimental and numerical studies have explored the propagation of flames through disperse sprays. Whilst flame propagation in a mist of very small droplets was similar to the case of a homogeneous mixture, larger droplets were found to have a positive effect on the burning velocity [2, 3]. In a numerical study of flame propagation in quiescent sprays, Neophytou and Mastorakos [5] showed that the effective equivalence ratio, as compared to the overall equivalence ratio, was an important parameter with respect to the burning velocity. Direct numerical simulations (DNS) showed that the flame propagation consisted of the successive ignition of flames engulfing individual droplets [6] and that premixed and non-premixed combustion modes co-exist in spray flames [7,8,9]
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