Effect of flame characteristics on an isolated ethanol droplet evaporating through stagnation methane/air flames: An experimental and numerical study

Abstract

A single ethanol droplet evaporation through laminar methane/air stagnation flame is investigated at lean, stoichiometric and rich conditions experimentally and numerically. For the droplets having initial diameters of 20-70μm, the particle Reynolds number is measured via PIV/PTV, resulting in the slip velocity between the droplet and gas flow being small and the surrounding gas being able to carry without any significant convective effects. Evaporation rates, computed from Abramzon–Sirignano for a moving droplet towards a stagnation flame field, satisfy the ones computed from empirically determined evaporation rates from ILIDS measurements as a function of flame temperature, flame speed and flame thickness. Nevertheless, Abramzon–Sirignano model slightly overestimates the vaporization constant for lean cases. The distance traveled by the droplet after leaving the flame zone determines the average critical diameter. Accordingly, droplets larger than 18μm can cross the flame, leading to local modifications in the flame region due to heat loss and vapor diffusion from the droplet. Novelty and Significance Energy conversion in combustion should be carried out by optimizing efficiency, minimizing pollution, and preventing further climate change. The multiphase nature of spray combustion particularly adds further complexity due to the strong coupling of atomization, evaporation, mixing, turbulence, and chemical reactions. Although spray combustion involves a cloud of polydispersed droplets, it is of fundamental importance to understand the dynamics of an isolated droplet and its interactions with the flame front, which can provide indispensable information for spray combustion models. In this study, an experimental and computational framework has been developed to investigate droplet-flame interactions. The dynamics and evaporation characteristics of an isolated droplets interacting with stagnation flames have been determined by coupling several laser diagnostics, while further enhanced with Eulerian–Lagrangian simulations under flame conditions. Thereupon, the outcomes help the design of injectors of spray combustion systems and enhancement of evaporation models.