The role of fatty acid structure in various pure vegetable oils on flame characteristics and stability behavior for industrial furnace

Abstract

This study investigates the effects of the fatty acid composition of various vegetable oils on the behavior of flames in the combustion process. The research is important for the substitution of fossil fuel using environmentally friendly vegetable oil. Five oils were tested including coconut oil, palm kernel oil, cotton seed oil, ceiba petandra oil and jatropha curcas oil. The oils were burned on an open tray at various air speeds performing three combustion regions, i. e., premixed combustion at the upstream region followed by transition region and diffusion combustion region at the downstream. Flame stability was tested at an air speed of 49 cm/s, 55 cm/s, and 64 cm/s. The image of the flame was recorded using a high-speed video camera at the rate of 200 frames per second. The flame temperature was measured by the K-type thermocouple. The results show that the higher saturated fatty acid content makes the flame brighter and more wavelet numbers present at the flame front maintaining the flame stability at a wide range of air speeds. The saturated fatty acid has a high flash point which is difficult to be burned at the flame front and escaping to burn as diffusion flame at the downstream region. The fatty acid content also affects the flame color which is evident in jatropha curcas oil with mostly a premixed/blue flame color and producing the highest thermal energy, while coconut oil is mostly a diffusion flame/yellow color. The longer ignition delay is shown in coconut oil because of the high saturated fatty acid content. The higher the unsaturated fatty acid content makes the flame more unstable. This shows that the bright yellow diffusion flame color is a good source of radiation thermal energy for flame stability. The flame color and the flame stability data are very valuable for designing efficient and stable industrial furnace with vegetable oil. This study gives insight into the influence of fatty acid chemical structure and physical properties on the combustion characteristics for thermal energy production. When high-temperature gas is needed in the industrial furnace, vegetable oil with unsaturated fatty acids is the choice by keeping the lower air speed. But when the industrial furnace with stable combustion process is the goal, the oil with saturated fatty acids is the best for a wide range of air speeds.