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research-article

SIMULATION OF COMBUSTION RECESSION AFTER END-OF-INJECTION AT DIESEL ENGINE CONDITIONS

[+] Author and Article Information
Dorrin Jarrahbashi

School of Mechanical Engineering Georgia Institute of Technology, Atlanta, GA 30332
dorrin.jarrahbashi@me.gatech.edu

Sayop Kim

School of Aerospace Engineering Georgia Institute of Technology , Atlanta, GA 30332
sayopkim@gatech.edu

Caroline L. Genzale

School of Mechanical Engineering Georgia Institute of Technology, Atlanta, GA 30332
caroline.genzale@me.gatech.edu

1Corresponding author.

ASME doi:10.1115/1.4036294 History: Received February 15, 2017; Revised February 21, 2017

Abstract

Recent experimental observations show that lifted diesel flames tend to propagate back towards the injector after the end of injection under conventional high-temperature conditions. The term “combustion recession” has been adopted to reflect this process. This phenomenon is closely linked to the end-of-injection entrainment and its impact on the transient mixture-chemistry evolution upstream of the lift-off length. A few studies have explored the physics of combustion recession with experiments and simplified modeling, but the details of the chemical kinetics and convective-diffusive transport of scalars and the capability of engine CFD simulations to accurately capture them are mainly unexplored. In this study, highly-resolved numerical simulations have been employed to explore the mixing and combustion of a diesel spray after the end of injection and the influence of modeling choices on the prediction of these phenomena. The simulations are centered on a temperature sweep around the Engine Combustion Network (ECN) Spray-A conditions, from 800 – 1000 K, where different combustion recession behaviors are observed experimentally. Reacting spray simulations are performed via OpenFOAM, using a RANS with a Lagrangian-Eulerian framework. Two reduced chemical kinetics models for n-dodecane are used to evaluate the impact of low-temperature chemistry and mechanism formulation on predictions of combustion recession. Observations from the simulations are consistent with recent findings that a two-stage auto-ignition sequence drives the combustion recession process. Simulations with two different chemical mechanisms indicate that low-temperature chemistry reactions drive the likelihood of combustion recession.

Copyright (c) 2017 by ASME
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