Abstract
Understanding the combustion behavior of gel fuel droplets is pivotal for enhancing burn rates, lowering ignition delay and improving the operational performance of next-generation propulsion systems. Vapor jetting in burning gel fuel droplets is a crucial process that enables an effective transport (convectively) of unreacted fuel from the droplet domain to the flame zone and accelerates the gas-phase mixing process. Here, first we show that the combusting ethanol gel droplets (organic gellant laden) exhibit a new oscillatory jetting mode due to aperiodic bursting of the droplet shell. Second, we show how the initial gellant loading rate (GLR) leads to a distinct shell formation which self-tunes temporally to burst the droplet at different frequencies. Particularly, a weak-flexible shell is formed at low GLR that undergoes successive rupture cascades occurring in same region of the droplet. This region weakens due to repeated ruptures and causes droplet bursting at progressively higher frequencies. Contrarily, high GLRs facilitate a strong-rigid shell formation where consecutive cascades occur at scattered locations across the droplet surface. This leads to droplet bursting at random frequencies. This method of modulating jetting frequency would enable an effective control of droplet trajectory and local fuel-oxidizer ratio in any gel-spray based energy formulation.
Highlights
The success of future rocket propulsion systems will depend on their ability to utilize eco-friendly fuels that exhibit high exothemicity, shortened ignition delay time, high energy density and operational safety at low cost[1, 2]
In gel fuel droplets the rupture of gellant shell is not accompanied by the formation of any daughter droplets (DDs) but results in jetting out of unreacted fuel vapors through ruptured portion of the shell, thereby releasing the internal pressure
Each cycle features a sequential four stage process of: (1) Gellant layer rupture at a weak soft spot. This is a key stage that results in the hole formation and provides an opening for the outflux of unreacted fuel vapors via jetting
Summary
The success of future rocket propulsion systems will depend on their ability to utilize eco-friendly fuels that exhibit high exothemicity, shortened ignition delay time, high energy density and operational safety at low cost (i.e. easy to store and handle)[1, 2] In this light, there has been a considerable interest in high-performance gellant based fuels as alternatives to conventional neat propellants[3,4,5,6,7,8,9,10]. In gel fuel droplets the rupture of gellant shell is not accompanied by the formation of any DDs but results in jetting out of unreacted fuel vapors through ruptured portion of the shell, thereby releasing the internal pressure. Literature search reveals that most studies have focused on jet visualization at the flame scale while the identification of different jetting modes, their initiation mechanisms and methods to control them at the droplet scale has received little attention
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
