An experimental and kinetic modeling study of the auto-ignition of natural gas blends containing C1–C7 alkanes

A Abd El-Sabor Mohamed,Snehasish Panigrahy,Amrit Bikram Sahu,Gilles Bourque,Henry J Curran

doi:10.1016/j.proci.2020.06.015

Abstract

Ignition delay time measurements for multi-component natural gas mixtures were carried out using a rapid compression machine at conditions relevant to gas turbine operation, at equivalence ratios of 0.5–2.0 in ‘air’ in the temperature range 650–1050 K, at pressures of 10–30 bar. Natural gas mixtures comprising C1–C7n-alkanes with methane as the major component (volume fraction: 0.35–0.98) were considered. A design of experiments was employed to minimize the number of experiments needed to cover the wide range of pressures, temperatures and equivalence ratios. The new experimental data, together with available literature data, were used to develop and assess a comprehensive chemical kinetic model. Replacing 1.875% methane with 1.25% n-hexane and 0.625% n-heptane in a mixture containing C1–C5 components leads to a significant increase in a mixture's reactivity. The mixtures containing heavier hydrocarbons also tend to show a strong negative temperature coefficient and two-stage ignition behavior. Sensitivity analyses of the C1–C7 blends have been performed to highlight the key reactions controlling their ignition behavior.

Highlights

The results showed an increase in negative temperature coefficient (NTC) behavior and a decrease in the onset of ignition temperature with increasing concentrations of higher order hydrocarbons in the mixtures
Ignition delay time measurements for C1–C7 n-alkanes blends were performed by using NUI Galway rapid compression machines (RCMs) at conditions relevant to gas turbine (GT) operating conditions
Six compositions of natural gas mixtures with methane being the major component were chosen for the study

Summary

Introduction

To achieve highly efficient and safe use of NG, experimental and kinetic modeling studies are needed for a wide range of NG mixtures to verify their varying combustion characteristics. Methane, being a major component of NG, has been studied extensively in the literature [3,4,5,6,7,8] and there are many available mechanisms describing its oxidation at conditions relevant to combustion devices [9,10,11,12,13]. Studying blends of alkanes with compositions similar to available sources of NG can provide tangible targets in predicting the combustion characteristics of these alternate NG mixtures to test their suitability for use in practical combustors

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Conclusion