The Structure of the Auto-Ignition Region of Turbulent Dilute Methanol Sprays Issuing in a Vitiated Co-flow

O'Loughlin, William; Masri, Assaad R.

doi:10.1007/s10494-012-9388-x

Cited by 37 publications

(26 citation statements)

References 35 publications

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“…This is also in accord with the ε − T map ( Figure 11). The role that CH 2 O plays along with H 2 O 2 and HO 2 as a precursor to ignition is consistent with experimental findings [3,94]. Figure 13 shows the evolution of OH mass fraction versus equivalence ratio during the ignition period.…”

Section: Early Flame Evolutionsupporting

confidence: 84%

Large eddy simulation of turbulent spray combustion

Irannejad

Banaeizadeh

Jaberi

2015

Combustion and Flame

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The two-phase filtered mass density function (FMDF) method is employed for large eddy simulation (LES) of high speed evaporating and combusting nheptane sprays using simple (global) and complex (skeletal) chemical kinetic mechanisms. The resolved fluid velocity and pressure fields are obtained by solving the filtered compressible Navier-Stokes equations with high-order Eulerian finite difference methods. The liquid spray and gas scalar (temperature and species mass fractions) fields are both obtained by Lagrangian stochastic models. The chemistry calculation is accelerated by incorporating the parallel in situ adaptive tabulation (ISAT) method. There are two-way interactions among Eulerian and Lagrangian fields. Simulations of evaporating sprays with and without combustion indicate that the two-phase LES/FMDF results are consistent and compare well with the available experimental data at different gas temperatures and oxygen concentrations. The spray controlled flame tends to move away from a diffusion flame structure toward a premixed one as the oxygen concentration decreases and/or the ambient gas temperature increases because of changes in spray-induced turbulence and mixing. The LES/FMDF results for ignition delay show more sensitivity to the chemical kinetic model at lower gas temperatures due to slower reaction and stronger turbulence-chemistry interactions. The liftoff length is less sensitive to the kinetics.

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Section: Early Flame Evolutionsupporting

confidence: 84%

Large eddy simulation of turbulent spray combustion

Irannejad

Banaeizadeh

Jaberi

2015

Combustion and Flame

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“…CH2O is produced in the low temperature oxidation process and consumed in the subsequent high temperature oxidation. Formaldehyde LIF was used for autoignition of methane jets [6], methanol, ethanol and acetone spray jet flames [7,8], and diesel fuel [9][10][11] and n-heptane [11,12] in HCCI engines. Najm et al [13] conducted detailed chemical kinetic computations of methane premixed flame and found that the concentration of formyl radical (HCO) is very well correlated with flame heat release rate.…”

Section: Introductionmentioning

confidence: 99%

Reaction zone visualisation in swirling spray n-heptane flames

Yuan

Kariuki

Dowlut³

et al. 2015

Proceedings of the Combustion Institute

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Joint PLIF measurements of CH2O and OH were performed in a swirl-stabilized nheptane spray flame at conditions close to extinction. Simulations of laminar counterflow heptane flames at different strain rates showed that the heat release could be approximately represented by the product CH2OxOH, but also that this product cannot visualise the heat release at the lean side of stoichiometry. The simulations suggest that the outline of CH2O regions in PLIF images could be an approximate indicator of the stoichiometric mixture fraction iso-line. Due to the intense turbulence and local extinction, individual PLIF images show a very variable behaviour. They indicate rich zones, reaction sheet breaks, lift-off, and they suggest that this flame is mostly of non-premixed character. The mean heat release rate as represented here is consistent with inverse Abel-transformed OH* chemiluminescence imaging. The usefulness of this technique for spray flames is discussed.

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“…The initial diameter is 20μm in C1 case and 12μm in C2 case. The initial diameter is in the same magnitude with the droplets SMD diameter (40μm) in the experiment (O'Loughlin, 2012) in which the droplets are achieved from an ultrasonic generator (Sonotek). The initial diameter is a little larger than that in the reference (Wang et al 2014).…”

Section: Computational Setupmentioning

confidence: 98%

A study on heat release rate indicator in the auto-igniting droplets using direct numerical simulation

Chen

2016

JTST

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Local heat release rate is one of the most concerned parameters in the combustion processes. However, this parameter is hard to be measured directly in the experiments. Therefore local heat release rate indicators have been sought and evaluated, and many works focus on the study in the gaseous laminar or turbulent premixed flames. The motivation of this work is to explore and validate heat release rate indicators for auto-igniting n-heptane droplets. To this end, direct numerical simulation (DNS) is performed with a detailed chemical reacting mechanism. Results show that the product of mass fractions of OH and CH 2 O is a proper indicator when the local auto-ignition prevails and the temperature rises quickly. The elementary reactions involved are analyzed, which shed light on the construction and performance of heat release rate indicators. Some new definitions of the indicators are proposed and evaluated. The proportional relationship between the indicator and the actual local heat release rate is determined. The heat release associated with different combustion regimes are distinguished, which reveals the dominant role of premixed flames in the droplets auto-ignition processes. Currently, most of the reported HRIs are for gaseous laminar and turbulent premixed flames. Their validity and performance in the two-phase combustion or in higher hydrocarbons flames need be evaluated. More importantly, the mechanism of what makes it a proper HRI or how to find a good HRI has not been investigated systematically. The quantitative relationship between the indicator and the actual local heat release rate is not yet determined in the turbulent studies. This paper aims to make a contribution to the above issues by numerical simulation. Direct numerical simulation (DNS) is performed to study the HRIs for the auto-igniting n-heptane droplets distributed in the hot vitiated flow.DNS is believed to resolve the turbulence completely, and it has been extended to the study of two-phase combustion. Auto-ignition of the liquid droplets in hot circumstance is one interested topic of DNS (Baba and Kurose 2008;Fujita et al. 2013;Kitano et al. 2013). The specific methods include two dimensional (2D) DNS coupled with the detailed reacting mechanism (Wang and Rutland 2007;Yoo et al. 2009;Wang and Rutland 2005) and 3D DNS coupled with the simplified reacting mechanism (Wang et al. 2012;Schroll et al. 2009;Wang et al. 2014). The effects of the relevant parameters, e.g. the overall equivalence ratio, the droplet diameter and its distribution, the initial gas temperature, pressure on ignition delay time were examined Rutland 2005, 2007;Im et al. 1998). So far, 3D DNS coupled with the detailed reacting mechanism (Borghesi et al. 2013) is rare due to huge requirement of calculation resources. Meanwhile, DNS also favors to the optimization of the related models in gaseous or two-phase combustion simulation. For instance, the droplets evaporation model coupled with the detailed chemical reacting mechanism is a concerned issue. Recently...

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The Structure of the Auto-Ignition Region of Turbulent Dilute Methanol Sprays Issuing in a Vitiated Co-flow

Cited by 37 publications

References 35 publications

Large eddy simulation of turbulent spray combustion

Large eddy simulation of turbulent spray combustion

Reaction zone visualisation in swirling spray n-heptane flames

A study on heat release rate indicator in the auto-igniting droplets using direct numerical simulation

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