Abstract
The aim of this paper is to analyze the self-ignition of a jet flame in hot vitiated cross flow using Large Eddy Simulation with analytically reduced chemistry. A rich premixed ethylene-air mixture (phi = 1.2) at 300 K is injected into a hot vitiated crossflow at 1500 K. The simulated reacting flow steady-state was validated against experiments in previous publications and the focus of the present work is the transient self-ignition of the jet. It is shown that spontaneous ignition occurs at very lean mixture fractions in the form of reacting patches in the windward jet mixing layer. These patches grow, laterally wrap the jet and extend into the recirculation region. Chemical explosive mode analysis is performed to identify the chemically active regions that are precursors of the patches undergoing spontaneous ignition. It is shown that the self-ignition occurs at very lean fuel concentrations regions, which are leaner and hotter than the most reactive mixture fraction of the jet and crossflow. This is explained by the fact that the scalar dissipation is significantly lower in these very lean regions. Ultimately, the peak heat release moves toward the richer regions and an autoignition cascade governs the steady state flame anchoring.
Highlights
The jet in crossflow (JICF) configuration has been widely studied over the past 80 years, see Margason (1993), due to its significant technological interest
This study investigates the transient self-ignition process of a cold premixed ethylene-air jet in hot vitiated crossflow using large eddy simulation and analytically reduced chemistry
There, autoignition conditions are met, i.e. very lean mixture fractions, high temperature, low scalar dissipation rates, moderate shear, and low flow velocity. These patches initiate a process of heat release diffusion that make richer mixtures more reactive and lead to their expansion around the jet and to an exponential growth of heat release magnitude. These lateral reactive fronts wrap up the jet and merge in the leeward region where autoignition conditions are not found
Summary
The jet in crossflow (JICF) configuration has been widely studied over the past 80 years, see Margason (1993), due to its significant technological interest. This configuration generates a complex flow field allowing for fast mixing rates of 2 streams. Less is known about reactive JICF (RJICF), where experimental studies have been mainly conducted for non-premixed configurations with jets being composed of pure fuel or N 2-diluted fuel, e.g. Pinchak et al (2019) investigated experimentally a RJIJCF configuration of premixed ethylane-air. They determined that for crossflow temperatures of 900 K, the flame stabilization mode was controlled by propagation rather than autoignition. Kolla et al (2012) simulated by DNS a RJICF and studied the blowout phenomenon dynamics due to kinematic imbalance between flame propagation speed and flow normal velocity
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