M.Sc Student M.Sc Thesis Yokev Neta An Investigation of Water-in Fuel Emulsion Spray Combustion Department of Aerospace Engineering PROFESSOR EMERITUS Jerrold Greenberg

Abstract

In today’s world, fuel efficiency is the center of attention in nearly every field of combustion. The economic burden of fuel consumption of vehicles is the hottest topic in the car and aerospace industries, and environmental consequences of inefficient burning of fuel through the 20th century led to an all-time-high rise of 𝐶𝑂2 and 𝑁𝑂x in the atmosphere. These problems led researchers of fuel combustion to explore new ways to increase efficiency of fuel usage, such as through the use of emulsions. It was found that the introduction of water in the fuel droplet prevents the fuel from peaking at extreme temperatures where soot and pollution are produced at high rates. Moreover, the water inside the fuel evaporates at a fast pace and ruptures the host droplet in a phenomenon called microexplosion. It provides a secondary atomization where fuel droplets are broken into smaller droplets, which evaporate more quickly, and burn more completely.

Investigating such complex combustion processes requires solving non-linear, partial differential equations for the heterogeneous mixture of water-in-fuel emulsion droplets. The solution requires major changes in the droplet properties due to the high rate of heat generated by the combustion reaction. Moreover, phase-change, flow complexity, energy, momentum and mass conservation are all non-linear, which makes the mathematical solution especially complicated. In order to reach meaningful conclusions from this problem, there is a need to simplify the physical issues using appropriate arguments and streamline the work using fundamental simplified models. Thus, in the current work a preliminary model of the behavior of a laminar rich off- stoichiometric water-in-fuel emulsion spray flame is tackled. In this research, the sectional method was applied to emulsions for the first time, and an asymptotic approach was adopted to obtain a solution. The solution consisted of an analytical solution, which was used to compute parameters such as the steady-state velocity. It was found that in the fuel-rich case, increasing the water content and\or droplet loading within the droplet decreases the velocity of the flame. Furthermore, the losses obtained by the microexplosion case were far more significant than those in the case without microexplosion. A stability analysis was performed for the flame of a fuel-rich mixture of emulsion droplets, in order to determine which parameters affect the neutral stability boundaries of the flame. It was found that both the initial water content and the droplet loading increase the instability of the flame. Just like the steady-state solution, it was found that the instability limit of microexplosion is far greater than that in the case without microexplosions.