Comparison of Sooting behavior amongst various Liquid Fuels

Abstract

Hydrocarbon combustion at fuel – air equivalence ratio (φ) greater than 1 results in incomplete combustion and formation of black flaky substance, soot. Soot is found responsible for health ailments, global warming and degradation of combustor performance in aircrafts. The study aims at determining the sooting threshold for various fuel samples and correlation of fuel chemical composition with sooting threshold. Premixed laminar combustion of fuel samples is observed on the Meker burner setup for varying fuel – air equivalence ratio (φ). The air flow rate and pressure are kept constant while the flow rate of liquid fuel through the plane jet atomizer assembly is varied with a flow control in – line rotameter and a constant feed pressure. By varying the fuel flow rate, φ is varied which causes changes in the flame. At rich φ , a bright yellow streak of soot is observed which vanishes when the fuel supply is reduced. This allows in determining the exact value of φ at which the sooting begins, called incipient sooting or sooting threshold. Aromatic compounds show a lower soot threshold due to their ease of forming poly – aromatic hydrocarbons which are the base constituent of soot particulate matter. In succession to aromatic compounds, dicyclic paraffins also lead to lower sooting thresholds. Iso – paraffins, cyclo – paraffins and n – paraffins have a comparatively higher sooting threshold. Experimental results show HRJ – tallow to have the highest sooting threshold with a φ of ~ 1.61 and Gevo jet blend a close second with φ ~ 1.53.