Laser-Based Experimental and Monte Carlo PDF Numerical Investigation of an Ethanol/Air Spray Flame

Abstract

A turbulent ethanol spray flame is characterized through quantitative experiments using laser-based imaging techniques. The experimental data set is used to validate a numerical code for the simulation of spray combustion. The spray burner has been constructed to facilitate the computational treatment of the experiment; in particular the spray flame is stabilized without a bluff body or a pilot flame. The experiments include spatially resolved measurements of droplet sizes (Mie/LIF-dropsizing and PDA), droplet velocity (PDA), liquid-phase temperature (two-color LIF temperature imaging with Rhodamine B) and gas-phase temperature (multi-line NO-LIF temperature imaging). The measurements close to the nozzle exit are used to determine the initial conditions for numerical simulations. A novel probability density function (PDF) method is applied to calculate the development of the spray flame. A joint mixture fraction and enthalpy PDF is formulated. Its transport equation is modeled and solved using a Monte-Carlo method. A detailed ethanol/air combustion mechanism consisting of 38 species and 337 elementary reactions is implemented through the spray flamelet model enabling the prediction of pollutant emission in spray flames. Good agreement with the experimental data is found for the gas temperature. The numerical predictions for the liquid-phase temperature are in reasonable agreement with the experimental data. The flame structure with two reaction zones is compared with other spray flames, and it is analyzed with the help of the experimental and numerical results. The formation mechanism of such a structure is revealed.