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Effect of methane on pilot-fuel auto-ignition in dual-fuel engines

Abstract : The ignition behavior of n-dodecane micro-pilot spray in a lean-premixed methane/air charge was investigated in an optically accessible Rapid Compression-Expansion Machine at dual-fuel engine-like pressure/temperature conditions. The pilot fuel was admitted using a coaxial single-hole 100 µm injector mounted on the cylinder periphery. Optical diagnostics include combined high-speed CH2O-PLIF (10 kHz) and Schlieren (80 kHz) imaging for detection of the first-stage ignition, and simultaneous high-speed OH* chemiluminescence (40 kHz) imaging for high-temperature ignition. The aim of this study is to enhance the fundamental understanding of the interaction of methane with the auto-ignition process of short pilot-fuel injections. Addition of methane into the air charge considerably prolongs ignition delay of the pilot spray with an increasing effect at lower temperatures and with higher methane/air equivalence ratios. The temporal separation of the first CH2O detection and high-temperature ignition was found almost constant regardless of methane content. This was interpreted as methane mostly deferring the cool-flame reactivity. In order to understand the underlying mechanisms of this interaction, experimental investigations were complemented with 1D-flamelet simulations using detailed chemistry, confirming the chemical influence of methane deferring the reactivity in the pilot-fuel lean mixtures. This shifts the onset of first-stage reactivity towards the fuel-richer conditions. Consequently, the onset of the turbulent cool-flame is delayed, leading to an overall increased high-temperature ignition delay. Overall, the study reveals a complex interplay between entrainment, low T and high T chemistry and micro-mixing for dual-fuel auto-ignition processes for which the governing processes were identified
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Submitted on : Thursday, March 7, 2019 - 4:23:47 PM
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Aleš Srna, Michele Bolla, Yuri M Wright, Kai Herrmann, Rolf Bombach, et al.. Effect of methane on pilot-fuel auto-ignition in dual-fuel engines. Proceedings of the Combustion Institute, Elsevier, 2019, 37 (4), pp.4741-4749. ⟨10.1016/j.proci.2018.06.177⟩. ⟨hal-02060812⟩



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