Heat release rate markers for premixed combustion

Nikolaou, Zacharias M.; Swaminathan, Nedunchezhian

doi:10.1016/j.combustflame.2014.05.019

Cited by 85 publications

(47 citation statements)

References 24 publications

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“…This is evident from significant Note that there are no signs of localized flame extinction in case C in spite of large values of the Karlovitz number (i.e., Ka > 100). This is consistent with several previous DNS findings [30][31][32][33]. The above discussion suggests that distinctly different physical mechanisms are likely to govern the behavior of invariants in the three cases considered.…”

Section: Selected Regions Of Instantaneous Nondimensional Temperaturesupporting

confidence: 81%

Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

et al. 2016

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The distributions of flow topologies within the flames representing the corrugated flamelets, thin reaction zones, and broken reaction zone regimes of premixed turbulent combustion are investigated using direct numerical simulation data of statistically planar turbulent H 2 -air flames with an equivalence ratio φ = 0.7. It was found that the diminishing influence of dilatation rate with increasing Karlovitz number has significant influences on the statistical behaviors of the first, second, and third invariants (i.e., P , Q, and R) of the velocity gradient tensor. These differences are reflected in the distributions of the flow topologies within the flames considered in this analysis. This has important consequences for those topologies that make dominant contributions to the scalar-turbulence interaction and vortexstretching terms in the scalar dissipation rate and enstrophy transport equations, respectively. Detailed physical explanations are provided for the observed regime dependences of the flow topologies and their implications on the scalar dissipation rate and enstrophy transport.

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Section: Selected Regions Of Instantaneous Nondimensional Temperaturesupporting

confidence: 81%

Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

et al. 2016

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“…Regions of HRR are well predicted by the OH and CH 2 O concentrations, representative of the pixel-by-pixel product of the OHand CH 2 O-PLIF signals, in MILD and conventional non-premixed kerosene flames. This technique performs particularly well, in agreement with [38], at high rates of strain where peak HRR rates are large. This suggests that the experimental technique is a valid indicator of HRR for non-premixed kerosene spray flames.…”

Section: Discussionsupporting

confidence: 64%

“…This method would be valid as an experimental HRR marker only if laminar flame calculations show that the overlap of OH and CH 2 O mimics the local reaction zone. Such markers for HRR under MILD conditons have been discussed by Sidey and Mastorakos [6] for non-premixed methane counterflow flames with hot combustion product oxidiser and for methane and multi-fuel premixed systems by Minamoto and Swaminathan [37] and Nikolaou and Swaminathan [38]. Sidey and Mastorakos reported that the overlap of CH 2 O and OH was a good marker for the peak HRR location in MILD flames, in agreement with Minamoto and Swaminathan [37], although CH 2 O alone may offer a better correlation at higher rates of strain in CH 4 flames.…”

Section: Introductionmentioning

confidence: 99%

Simulations of laminar non-premixed flames of kerosene with hot combustion products as oxidiser

Sidey

Giusti

Mastorakos

2016

Combustion Theory and Modelling

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The effects of hot combustion product dilution in a pressurised kerosene-burning system at gas turbine conditions were investigated with laminar counterflow flame simulations. Hot combustion products from a lean (φ = 0.6) premixed flame were used as an oxidiser with kerosene surrogate as fuel in a non-premixed counterflow flame at 5, 7, 9 and 11 bar. Kerosene-hot product flames, referred to as 'MILD', exhibit a flame structure similar to that of kerosene-air flames, referred to as 'conventional', at low strain rates. The Heat Release Rate (HRR) of both conventional and MILD flames reflects the pyrolysis of the primary and intermediate fuels on the rich side of the reaction zone. Positive HRR and OH regions in mixture fraction space are of similar width to conventional kerosene flames, suggesting that MILD flames are thin fronts. MILD flames do not exhibit typical extinction behaviour, but gradually transition to a mixing solution at very high rates of strain (above A = 160, 000 s −1 for all pressures). This is in agreement with literature that suggests heavily preheated and diluted flames have a monotonic S-shaped curve. Despite these differences in comparison with kerosene-air flames, MILD flames follow typical trends as a function of both strain and pressure. Further still, the peak locations of the overlap of OH and CH 2 O mass fractions in comparison with the peak HRR indicate that the pixel-by-pixel product of OH-and CH 2 O-PLIF signals is a valid experimental marker for non-premixed kerosene MILD and conventional flames.

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“…as an indicator. The R6 reaction is also re-examined and studied in the methane-air and multi component fuel-air mixture based on the elementary reactions analysis in (Nikolaou et al 2014) and the performance in the multi component fuel flame is emphasized. Inspired by the above idea, the study also proposes new multiple-kind HRIs based on the major species mentioned in Table 2.…”

Section: Analysis Of the Elementary Reactions And Evaluation Of Diffementioning

confidence: 99%

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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Heat release rate markers for premixed combustion

Cited by 85 publications

References 24 publications

Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

Flow topologies in different regimes of premixed turbulent combustion: A direct numerical simulation analysis

Simulations of laminar non-premixed flames of kerosene with hot combustion products as oxidiser

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

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