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Importance of Turbulence-chemistry Interactions in Predicting Spray A End of Injection Phenomenon

University of Oxford-Xiaohang Fang, Riyaz Ismail, Nikola Sekularac, Martin Davy
  • Technical Paper
  • 2020-01-0779
To be published on 2020-04-14 by SAE International in United States
In this study, the role of turbulence-chemistry interaction in diesel spray auto-ignition, flame stabilisation and end of injection phenomenon is investigated under engine relevant Spray A conditions. A recently developed diesel spray combustion modelling approach, conditional source-term estimation (CSE-FGM), is coupled with Reynolds-averaged Navier-Stokes simulation (RANS) framework to study the details of spray combustion. The detailed chemistry mechanism is included in this approach through the flamelet generated manifold (FGM) method. Both unsteady and steady flamelet solutions are included in the manifold to account for the auto-ignition process and subsequent flame propagation in a diesel spray. Conditionally averaged chemical source terms are closed by the conditional scalars obtained in the CSE routine. Both non-reacting and reacting spray jets are computed over a wide range of Engine Combustion Network (ECN) diesel Spray A conditions. The reacting results are compared with simulations using homogeneous reactor combustion model and flamelet combustion model with the same chemical mechanism. The present study represents the first application of CSE for a diesel spray. The non-reacting liquid/vapour penetration, the mean and rms mixture…
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A Study on Kinetic Mechanisms of Diesel Fuel Surrogate n-Dodecane for the Simulation of Combustion Recession

University of Oxford-Xiaohang Fang, Riyaz Ismail, Martin Davy
Published 2019-04-02 by SAE International in United States
Combustion recession, an end of injection (EOI) diesel spray phenomenon, has been found to be a robust correlation parameter for UHC in diesel LTC strategies. Previous studies have shown that the likelihood of capturing combustion recession in numerical simulations is highly dependent on the details of the low-temperature chemistry reaction mechanisms employed. This study aims to further the understanding of the effects of different chemical mechanisms in the prediction of a reactive diesel spray and its EOI process: combustion recession. Studies were performed under the Engine Combustion Network’s (ECN) “Spray A” conditions using the Reynolds-Averaged Navier-Stokes simulation (RANS) and the Flamelet Generated Manifold (FGM) combustion model with four different chemical mechanisms for n-dodecane that are commonly used in the engine simulation communities - including recently developed reduced chemistry mechanisms. The flamelet database for each of the chemical mechanism is generated using two methods: 0D homogeneous reactor (HR) ignition flamelets and 1D igniting counterflow diffusion (ICDF) flamelets. The effect of different tabulation approaches is investigated first following by the discussion of the impact of chemical mechanisms…
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The Oxford Cold Driven Shock Tube (CDST) for Fuel Spray and Chemical Kinetics Research

University of Oxford-Joseph Camm, Martin Davy, Xiaohang Fang, Luke Doherty, Matthew McGilvray, Felix Foerster
Published 2018-04-03 by SAE International in United States
A new reflected shock tube facility, the Cold Driven Shock Tube (CDST), has been designed, built and commissioned at the University of Oxford for investigating IC engine fuel spray physics and chemistry. Fuel spray and chemical kinetics research requires its test gas to be at engine representative pressures and temperatures. A reflected shock tube generates these extreme conditions in the test gas for short durations (order milliseconds) by transiently compressing it through a reflected shock process. The CDST has been designed for a nominal test condition of 6 MPa, 900 K slug of air (300 mm long) for a steady test duration of 3 ms. The facility is capable of studying reacting mixtures at higher pressures (up to 150 bar) than other current facilities, whilst still having comparable size (100 mm diameter) and optical access to interrogate the fuel spray with high speed imaging and laser diagnostics. Future data gathered will support fundamental research for IC engine and fuel technologies leading to even higher thermal efficiency along with a reduction in emissions, and provide high quality, repeatable validation data for advanced…
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Comparison of Transient Diesel Spray Break-Up between Two Computational Fluid Dynamics Codes

Jaguar Land Rover Ltd.-David Richardson
University of Oxford-Louis Nicholson, Xiaohang Fang, Joseph Camm, Martin Davy
Published 2018-04-03 by SAE International in United States
Accurate modeling of the initial transient period of spray development is critical within diesel engines, as it impacts on the amount of vapor penetration and hence the combustion characteristics of the spray. In addition, in multiple injection schemes shorter injections will be mostly, if not totally, within the initial transient period. This paper investigates how two different commercially available Computational Fluid Dynamics (CFD) codes (hereafter noted as Code 1 and Code 2) simulate transient diesel spray atomization, in a non-combusting environment. The case considered for comparison is a single-hole injection of n-dodecane representing the Engine Combustion Network’s ‘Spray A’ condition. It was identified that the different spray break-up models used by the codes (Reitz-Diwakar for Code 1, Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) for Code 2) had a significant impact on the transient liquid penetration. From differing initial base setups, Code 1’s case was then matched as closely as possible to Code 2’s case, applying the KH-RT break-up model in Code 1 with the same constants for the break-up and turbulence models as in Code 2. Despite the nominal…
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