Impact of fuel chemistry on the global consumption speed of large hydrocarbon fuel/air flames

TL;DR

This study measures turbulent consumption speeds of large hydrocarbon fuels, revealing how chemical composition influences flame stability and speed, which is crucial for modeling and using alternative fuels.

Contribution

It provides experimental data on turbulent flame speeds for different hydrocarbon fuels, highlighting the impact of chemical composition on flame behavior and stability.

Findings

A2 (Jet-A) has the highest turbulent flame speeds and remains stable at lower equivalence ratios.

C1 fuel, with no aromatics, has the slowest flame speeds and is more sensitive to turbulence.

Chemical class differences significantly affect flame stretch sensitivity and stability.

Abstract

Large hydrocarbon fuels are used for ground and air transportation and will be for the foreseeable future. Despite their extensive use, turbulent combustion of large hydrocarbon fuels, remains relatively poorly understood and difficult to predict. A key parameter when burning these fuels is the turbulent consumption speed; the velocity at which fuel and air are consumed through a turbulent flame front. Such information can be useful as a model input parameter and for validation of modeled results. In this study, turbulent consumption speeds were measured for three jet-like fuels using a premixed turbulent Bunsen burner. The burner was used to independently control turbulence intensity, unburned temperature, and equivalence ratio. Each fuel had similar heat releases (within 2%), laminar flame speeds (within 5-15 %), and adiabatic flame temperatures. Despite this similarity, for constant Re_D and turbulence intensity, A2 (i.e., jet-A) has the highest turbulent flame speeds and remains stable (i.e., without tip quenching) at lower {\phi} than the other fuels evaluated. In contrast the C1 fuel, which contains no aromatics, has the slowest turbulent flame speeds and exhibits tip quenching at higher {\phi} then the other fuels. C1 was the most sensitive to the influence of turbulence, as evidenced by this fuel having the largest ratio of turbulent to laminar flame speeds. The C1 fuel had the highest stretch sensitivity, in general, as indicated by calculated Markstein numbers. This work shows that turbulent flame speeds and tip stability of multi-component large hydrocarbon fuels can be sensitive to the chemical class of its components. The results from the current work indicate that caution may be needed when using alternative or surrogate fuels to replicate conventional fuels, especially if the alternative fuels are missing chemical classes of fuels that influence stretch sensitivities.