Unsteady solutions of the spray flamelet equations

TL;DR

This paper develops a new unsteady spray flamelet model using a Lagrangian approach, enabling analysis of transient liquid-gas interactions and the impact of injection strategies on flame stability and temperature.

Contribution

It introduces a Lagrangian-based formulation for unsteady spray flamelet equations, allowing for the first time the study of transient spray effects on flame behavior.

Findings

Discontinuous droplet injection can significantly enhance flame temperature.

The model shows that initial droplet size and velocity influence flame stability.

Unsteady interactions between liquid and gas phases are critical for accurate flame modeling.

Abstract

Solutions of the spray flamelet equations reported in the literature during the last decade have been limited to very specific situations presenting steady evaporation profiles only. In contrast, intrinsically unsteady interactions between the liquid and gas phases have received little attention so far. In this work, the spray flamelet equations are closed by means of a Lagrangian description of the liquid phase in mixture fraction space, which allows solving them for unsteady situations. The resulting formulation is then employed to conduct parametric analyses of the effects of initial droplet radius and velocity variations on ethanol/air non-premixed gas flamelets perturbed by sprays generated with different droplet injection strategies. Special emphasis is given to the differences between continuous and discontinuous droplet injection. The results illustrate how the latter can considerably increase the temperature and stability of flamelet structures, provided the spray parameters are appropriately selected.