Conditional moment closure and G-equation hybrid modelling For dual-fuel methane/N-heptane combustion

Abstract

Lean premixed combustion of natural gas in IC engines is attractive since it combines low emissions with diesel-like efficiencies due to the high knock resistance of natural gas. The low ignition propensity of natural gas however poses significant challenges in terms of robust combustion initiation with conventional spark plugs, especially at lean conditions. Dual-fuel combustion, where a more reactive diesel micro pilot is injected to provide a reliable source of ignition for the natural gas, constitutes a very promising alternative. Following ignition, flame propagates through a partially-reacted and inhomogeneous mixture of the two fuels. This study formulates and tests turbulent combustion modelling for dual-fuel engines using different models depending on the flame burning mode. The hybrid model combines Conditional Moment Closure (CMC) modelling, accounting for the autoignition of the n-heptane spray, with the G-equation model describing the subsequent flame propagation. The modelling is tested against previous measurements of dual-fuel methane/n-heptane combustion in a Rapid Compression Machine experiment. The new numerical methodology couples the models to account for the heat release from both fuels and can be used for the full range of fuel substitution, from pure diesel to pure natural gas engines. The results present a good agreement with experimental data with respect to cumulative heat release.

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ORCID for Edward Richardson: orcid.org/0000-0002-7631-0377

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