Influence of Fuel Characteristics in a Correlation to Predict Lean Blowout of Bluff-Body Stabilized Flames

Abstract

This study employed experimental data collected at the Air Force Research Laboratory (AFRL) as well as data from a review of past literature to develop a correlation for predicting lean blowout through the use of a least-squares curve-fit method. Combining data from the literature with data from AFRL allowed significant variations within the dataset with regard to velocity, flameholder diameter and shape, pressure, temperature, and fuel. Gaseous, single-component fuels as well as multi-component jet fuels were included in the study. The study reports new jet fuel blowout data. The laminar flame speed and ignition delay time calculated using detailed chemical kinetics mechanisms were used in the correlations to determine the chemical timescales relevant to lean blowout. The correlation presented here indicates that the lean blowout of bluff-body stabilized flames is dependent on the Damköhler number, with fuel variation being a significant factor. The ratio of the flameholder diameter to the lip velocity was found to influence the lean blowout. This ratio represents the fluid-mechanic timescale in the Damköhler number. Pressure, temperature, and the hydrogen-to-carbon ratio of the fuel affect the reactivity of the mixture, contributing to the chemical timescale in the Damköhler number. For a limited dataset, the ignition delay time is an adequate representation of the chemical timescale.