A computational study and correlation of premixed isooctane air laminar reaction fronts diluted with EGR

Middleton, Richard H.; Martz, Jason; Lavoie, George A.; Babajimopoulos, Aristotelis; Assanis, Dennis N.

doi:10.1016/j.combustflame.2012.04.014

Cited by 50 publications

(40 citation statements)

References 37 publications

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“…The results showed that differences in burn duration between the cases were due to variations in the mixture ratio of specific heats, which affected the work transfer between the earlier and later burning portions of the HCCI charge. Laminar flame simulations by Middleton et al [13] indicated laminar burning velocities decreased with increased levels of EGR dilution (vs. air dilution) due to thermal and chemical effects. Flame speed was shown to be most sensitive to the high temperature chain branching and chain terminating reaction rates which were affected by the mixture O 2 concentration.…”

Section: Introductionmentioning

confidence: 95%

“…Laminar flame simulations have predicted that premixed flames can be sustained under ultra-dilute conditions provided that T b exceeds $1450-1500 K [10][11][12][13]; otherwise, flame quenching can be induced by processes such as turbulent strain or external heat loss [14][15][16][17]. It has been proposed based upon dimensional analysis that when the flame thickness exceeds the smallest scales of the turbulent flow, transport rates within the flame are increased, broadening it to the point where there is a sharp drop in temperature that leads to flame extinction.…”

Section: Introductionmentioning

confidence: 99%

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On the sensitivity of low temperature combustion to spark assist near flame limit conditions

Olesky

Middleton

Lavoie

et al. 2015

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h i g h l i g h t sThe effect of spark assist on air and EGR dilute HCCI combustion was examined. Spark had greater combustion advance effect on more air dilute (vs. EGR dilute) mixtures. Combustion advance was caused by an increased fraction of flame-based heat release. Flame quenching likely affected mixtures that showed a non-response to spark assist. a b s t r a c t Spark assisted compression ignition (SACI) is a practical mode for controlling the heat release rate of low temperature combustion (LTC). While flames are key phenomena in the SACI combustion process, they may not always be effective or viable under the mildly stratified and highly dilute low burned gas temperature conditions of LTC. To better understand the limits of flammability or flame effectiveness, this work explores combustion within a single cylinder direct injection engine near the high load limit of the HCCI combustion regime, where spark induced flame propagation has been seen to affect combustion phasing and heat release rate. Flame limiting conditions were identified using progressively more advanced spark timing, up to 120°before top dead center, for differing levels of air and EGR dilution while holding the chemical energy content of the charge constant. Under air dilute conditions, the measured combustion phasing advanced from 8°to 0°after top dead center with spark advance, while almost no effect was seen under EGR dilute conditions. Estimates of the experimental global and local state conditions were made at the time of spark using heat release analysis and a KIVA-3V engine model, respectively, and the flammability for each case was evaluated using the Karlovitz criterion. The results show that fuel rich stratification near the spark plug was likely responsible for the observed variations in the SACI flame behavior.

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Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

On the sensitivity of low temperature combustion to spark assist near flame limit conditions

Olesky

Middleton

Lavoie

et al. 2015

Fuel

Self Cite

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“…The recent correlations developed by Middleton et al [22] were used to calculate the laminar flame speed during the flame propagation portion of the cycle. The correlations were developed for iso-octane for a wide range of conditions, including temperatures and dilution levels relevant to SACI operating conditions.…”

Section: Two-zone Thermodynamic Model For Advanced Multi-mode Combustionmentioning

confidence: 99%

Enhanced heat release analysis for advanced multi-mode combustion engine experiments

et al. 2014

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“…It is assumed that the formation and early existence of localized flame-like structures, the primary concern of predictions in the present work, occur in a nominally constant pressure environment. Laminar flame speed values were calculated using the correlations developed by Middleton et al [11] for premixed iso-octane. The flame speed correlation was validated in that study by comparison with a wide range of experimental and computational works at initial temperatures between 298 and 1000 K. As a consequence, predictions of the location of the strong ignition limit in the present work were intentionally limited to initial temperatures less than $1100 K. Valid laminar flame speed data at higher temperatures would allow the predictions in the present work to be extended to higher temperatures.…”

Section: Computationalmentioning

confidence: 99%

Low-temperature ignition behavior of iso-octane

Mansfield

Wooldridge

et al. 2015

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h i g h l i g h t sAuto-ignition properties of air-dilute iso-octane investigated at low temperatures. Homogeneous and inhomogeneous behaviors observed, strong ignition limits identified. Sankaran Criterion accurately predicts location of strong ignition limit a priori. Measured ignition delay times compared to zero-dimensional model predictions.Accuracy of predictions affected by ignition behavior for u = 1.0, but not u = 0.25. a b s t r a c tAuto-ignition properties of iso-octane mixtures were systematically investigated at conditions relevant to practical combustion devices using the University of Michigan Rapid Compression Facility and the Tsinghua University Rapid Compression Machine. Pressure time history measurements and high-speed imaging of the ignition process were used in both facilities to determine auto-ignition delay times and directly observe physical ignition behaviors. Test mixtures used fuel-to-O 2 equivalence ratios of u = 0.25 and 1.0, and were air-dilute, i.e. molar O 2 to diluent gas (N 2 , Ar) ratio of 1:3.76. The pressures and temperatures after compression ranged from 3 to 30 atm and 740-1125 K respectively. The comprehensive results of the present work combined with those from previous shocktube studies clearly illustrate the existence of both inhomogeneous and homogeneous auto-ignition behaviors at these conditions. Analysis of patterns in the ignition behaviors revealed a dependence on initial unburned temperature and pressure, as well as equivalence ratio, with distinct regions of thermodynamic state in which the behavior is consistent and repeatable. The strong ignition limits were identified for both u using the experimental results and compared to predicted locations made using the Sankaran Criterion (the ratio of the laminar flame speed to the thermal gradient driven spontaneous propagation speed). Predictions made using an assumed thermal gradient of 5-10 K/mm were in excellent agreement with measurements at all conditions, clearly indicating that use of this criterion is an effective method for a priori prediction of auto-ignition behaviors for iso-octane. This validation of the Sankaran Criterion for iso-octane, an important reference hydrocarbon fuel, importantly broadens the use of this tool and is an indication that ignition processes in hydrocarbon and high hydrogen content fuels are fundamentally similar. Additionally, a comparison of the measured auto-ignition delay times to predictions made using zero-dimensional homogeneous reactor modeling revealed that for experiments with inhomogeneous ignition behaviors, agreement was dependent on u and the auto-ignition delay time. The presence of inhomogeneous ignition behavior did not significantly affect the accuracy of auto-ignition delay time predictions for mixtures with u = 0.25; whereas, for mixtures with u = 1.0 the presence of inhomogeneous ignition behavior significantly reduced the accuracy of predictions if the auto-ignition delay time was greater than $1 ms. These results indicate that while lowering u may not elimina...

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A computational study and correlation of premixed isooctane air laminar reaction fronts diluted with EGR

Cited by 50 publications

References 37 publications

On the sensitivity of low temperature combustion to spark assist near flame limit conditions

On the sensitivity of low temperature combustion to spark assist near flame limit conditions

Enhanced heat release analysis for advanced multi-mode combustion engine experiments

Low-temperature ignition behavior of iso-octane

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