Transported PDF Modeling of Ethanol Spray in Hot-Diluted Coflow Flame

Abstract

This paper presents a numerical modeling study of one ethanol spray flame from the Delft Spray-in-Hot-Coflow (DSHC) database, which has been used to study Moderate or Intense Low-oxygen Dilution (MILD) combustion of liquid fuels (Correia Rodrigues et al. Combust. Flame 162, 759-773, 2015). A "Lagrangian-Lagrangian" approach is adopted where both the joint velocity-scalar Probability Density Function (PDF) for the continuous phase and the joint PDF of droplet properties are modeled and solved. The evolution of the gas phase composition is described by a Flamelet Generated Manifold (FGM) and the interaction by exchange with the mean (IEM) micro-mixing model. Effects of finite conductivity on droplet heating and evaporation are accounted for. The inlet boundary conditions starting in the dilute spray region are obtained from the available experimental data together with the results of a calculation of the spray including the dense region using ANSYS Fluent 15. A method is developed to determine a good estimation for the initial droplet temperature. The inclusion of the "1/3" rule for droplet evaporation and dispersion models is shown to be very important. The current modeling approach is capable of accurately predicting main properties, including mean velocity, droplet mean diameter and number density. The gas temperature is under-predicted in the region where the enthalpy loss due to droplet evaporation is important. The flame structure analysis reveals the existence of two heat release regions, respectively having the characteristics of a premixed and a diffusion flame. The experimental and modeled temperature PDFs are compared, highlighting the capabilities and limitations of the proposed model.

Numerical study of the multi-flame structure in spray combustion

“…4 f shows that a large amount of CO is produced in RR1 of case H II . As shown in our previous study [22] , the RR2, which is also the main heat release region is actually created by the nonpremixed reaction between the CO and the O 2 from coflow. Fig.…”

Identification of Flame Regimes in Partially Premixed Combustion from a Quasi-DNS Dataset

“…Because of this, different authors have defined the flame index as the product of the normalized Takeno flame index multiplied by the heat release rate, chemical reaction rate or source term of the progress variable (Srinivasan et al 2015;Huang et al 2016;Eckel et al 2019): where Ṡ is the heat release rate, reaction rate of the fuel or reaction progress source term. Another approach of extending the definition range of the flame index is by using not a single species for the fuel, but the sum of selected species mass fractions: Different authors have proposed different sets of species depending on the flame setup (Lignell et al 2011;Jangi et al 2015;Minamoto et al 2015;Ma et al 2016;Pei et al 2016;Wei et al 2018;Pang et al 2018;Tufano et al 2018;Hu and Kurose 2019b;Wan et al 2019;Wen et al 2019;. 18angle…”

“…For example, the flame index based on fuel and oxidizer gradients is not applicable in regions of the flame where the fuel is completely consumed. Because of this, different multi-species extensions have been used in the past (Lignell et al 2011;Jangi et al 2015;Minamoto et al 2015;Ma et al 2016;Pei et al 2016;Wei et al 2018;Pang et al 2018;Tufano et al 2018;Hu and Kurose 2019b;Wan et al 2019;Wen et al 2019;. Fiorina et al (2005) found that even in laminar diffusion flames, the flame index concept can make wrong predictions.…”

Large Eddy Simulation of an ethanol spray flame under MILD combustion with the stochastic fields method

“…The measurements were conducted at TU Delft and further details can be found in the works by Roekaerts et al [7,8] . The same group also completed a numerical study investigating the same set-up using RANS starting their simulations at the first measurement location with good results [10] . The present work focuses on the applicability of the LES-pdf approach to MILD combustion together with the stochastic fields method for the continuous phase and a stochastic Lagrangian particles description of the dispersed phase.…”