Title: Numerical study of the ignition behavior of a post-discharge kernel in a turbulent stratified crossflow

Abstract

Ensuring robust ignition is critical for the operability of aeronautical gas-turbine combustors. For ignition to be successful, an important aspect is the ability of the hot gas generated by the spark discharge to initiate combustion reactions, leading to the formation of a self-sustained ignition kernel. This study focuses on this phenomena by performing simulations of kernel ignition in a crossflow configuration that was characterized experimentally. First, inert simulations are performed to identify numerical parameters correctly reproducing the kernel ejection from the ignition cavity, which is here modeled as a pulsed jet. In particular, the kernel diameter and the transit time of the kernel to the reacting mixture are matched with measurements. Considering stochastic perturbations of the ejection velocity of the ignition kernel, the variability of the kernel transit time is also reproduced by the simulations. Subsequently, simulations of a series of ignition sequences are performed with varying equivalence ratio of the fuel-air mixture in the crossflow. The numerical results are shown to reproduce the ignition failure that occurs for the leanest equivalence ratio ($φ = 0.6$). For higher equivalence ratios, the simulations are shown to capture the sensitivity of the ignition to the equivalence ratio, and the kernel successfully transitionsmore » into a propagating flame. Significant stochastic dispersion of the ignition strength is observed, which relates to the variability of the transit time of the kernel to the re- active mixture. An analysis of the structure of the ignition kernel also highlights the transition towards a self-propagating flame for successful ignition conditions.« less

Authors:

Jaravel, T. ^[1]; Labahn, J. ^[1]; Sforzo, B. ^[2]; Seitzman, J. ^[3]; Ihme, M. ^[4]

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+ Show Author Affiliations

1. Stanford Univ., CA (United States). Center for Turbulence Research
2. Argonne National Lab. (ANL), Argonne, IL (United States). Energy System Division
3. Georgia Inst. of Technology, Atlanta, GA (United States). Ben T. Zinn Combustion Lab., Guggenheim School of Aerospace Engineering
4. Stanford Univ., CA (United States). Center for Turbulence Research, and Dept. of Mechanical Engineering

Publication Date:

Tue Jan 01 00:00:00 EST 2019

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States)

Sponsoring Org.:

National Aeronautics and Space Administration (NASA)

OSTI Identifier:

1559043

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the Combustion Institute

Additional Journal Information:

Journal Volume: 37; Journal Issue: 4; Journal ID: ISSN 1540-7489

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

42 ENGINEERING; Finite-rate chemistry; Forced ignition; Gas-turbine ignition; Non-premixed flame