The effect of global equivalence ratio and postflame temperature on the composition of emissions from laminar ethylene/air diffusion flames

Abstract

Soot extinction, gas chromatography/mass spectrometry, on-line mass spectrometry, and tunable diode laser absorption spectroscopy (TDLAS) were used to monitor both condensed-phase and gas-phase combustion emissions from an enclosed, axisymmetric ethylene/air diffusion flame flow tube system. The system was operated at global equivalence ratios (GER) ranging from 0.52 to 1.52 (fuel-lean to fuel-rich). The temperature of the flow tube was varied from ambient conditions to 1273 K. Temperatures in the flow tube were measured using thermocouples. The velocity of the smoke particulate was measured using phase Doppler particle analysis (PDPA). It was found that the concentration of the gas-phase products of incomplete combustion increased as the GER was increased. Concentrations of CO 2 and soot showed maxima at GER = 1. Upon heating of the effluents, levels of CO and CO 2 increased, coincident with decreases in soot, oxygen, and acetylene levels at each GER. Polycyclic aromatic hydrocarbons (PAH) concentrations also increased with increasing GER. For overventilated cases, PAH levels decreased as the temperature of the tube furnace was increased. However, for the underventilated flames, PAH levels were found to rise to a temperature of ∼873 K, and then fall upon further temperature increases. The velocity and temperature measurements, coupled with the soot volume fraction measurements were used to calculate the soot oxidation rate, which appears to be in reasonable agreement with the Nagle Strickland-Constable (NSC) expression.