A large-eddy simulation study on the influence of diesel pilot spray quantity on methane-air flame initiation

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Abstract

The present study is a continuation of the previous work by Kahila et al. (2019), in which a dual-fuel (DF) ignition process was numerically investigated by modeling liquid diesel-surrogate injection into a lean methane-air mixture in engine relevant conditions. Earlier, the injection duration (tinj) of diesel-surrogate exceeded substantially the characteristic autoignition time scale. Here, such a pilot spray ignition problem is studied at a fixed mass flow rate but with a varying tinj. The focus is on understanding the influence of pilot quantity on spray dilution process and low- and high-temperature chemistry. In total, ten cases are computed with multiple diesel pilot quantities by utilizing a newly developed large-eddy simulation/finite-rate chemistry solver. The baseline spray setup corresponds to the Engine Combustion Network (ECN) Spray A configuration, enabling an extensive validation of the present numerical models and providing a reference case for the DF computations. Additionally, experimental results from a single-cylinder laboratory engine are provided to discuss the ignition characteristics in the context of a real application. The main results of the present study are: (1) reducing tinj introduces excessive dilution of the DF mixture, (2) dilution lowers the reactivity of the DF mixture, leading to delayed high-temperature ignition and slow overall methane consumption, (3) low enough pilot quantity (tinj < 0.3 ms) may lead to very long ignition delay times, (4) cumulative heat release is dominated by low/high-temperature chemistry at low/high tinj values, (5) analysis of the underlying chemistry manifold implies that the sensitivity of ignition chemistry on mixing is time-dependent and connected to the end of injection time, and 6) long ignition delay times at very low tinj values can be decreased by decreasing injection pressure.

Details

Original languageEnglish
Pages (from-to)506-521
Number of pages16
JournalCombustion and Flame
Volume206
Publication statusPublished - 30 May 2019
MoE publication typeA1 Journal article-refereed

    Research areas

  • Dual-fuel, ECN, Ignition, LES, Pilot, Spray A

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