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Abstract Experimentally measured values of the laminar flame speed (SL) are reported for the primary reference fuels over a range of unburned-gas temperatures (Tu) spanning from room temperature to above 1,000 K, providing the highest-temperature SL measurements ever reported for gasoline-relevant fuels. Measurements were performed using expanding flames ignited within a shock tube and recorded using side-wall schlieren imaging. The recently introduced area-averaged linear curvature (AA-LC) model is used to extrapolate stretch-free flame speeds from the aspherical flames. High-temperature SL measurements are compared to values simulated using different kinetic mechanisms and are used to assess three functional forms of empirical SL–Tu relationships: the ubiquitous power-law model, an exponential relation, and a non-Arrhenius form. This work demonstrates the significantly enhanced capability of the shock-tube flame speed method to provide engine-relevant SL measurements with the potential to meaningfully improve accuracy and reduce uncertainty of kinetic mechanisms when used to predict global combustion behaviors most relevant to practical engine applications.
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Improved correlations for the unstretched laminar flame properties of iso-octane/air mixtures
The unstretched laminar flame speed (LFS) plays a key role in engine models and predictions of flame propagation. It is also an essential parameter in the study of turbulent combustion and can be directly used in many turbulent combustion models. Therefore, it is important to predict the laminar flame speed accurately and efficiently. Two improved correlations for the unstretched laminar flame speed, namely improved power law and improved Arrhenius form correlations, are proposed for iso-octane/air mixtures in this study, using simulated results for typical operating conditions for spark-ignition engines: unburned temperatures of 300-950 K, pressures of 1-120 bar, and equivalence ratios of 0.6-1.5. The original data points used to develop the new correlations were obtained using the detailed combustion kinetics for iso-octane from Lawrence Livermore National Laboratory (LLNL). The three coefficients in the improved power law correlation were determined using a methodology different from previous approaches. The improved Arrhenius form correlation employs a function of unburned gas temperature to replace the flame temperature, making the expression briefer and making the coefficients easier to calculate. The improved Arrhenius method is able to predict the trends and the values of laminar flame speed with improved accuracy over a larger range of operating conditions. The improved power law method also works well but for a relatively narrow range of predictions. The improved Arrhenius method is recommended, considering its overall fitting error was only half of that using the improved power law correlation and it was closer to the experimental measurements. Even though ϕm, the equivalence ratio at which the laminar flame speed reaches its maximum, is not monotonic with pressure, this dependence is still included, since it produces least-rich best torque (LBT). The comparisons between the improved correlations in this study and the experimental measurements and the other correlations from various researchers are shown as well.
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- Award ID(s):
- 1650483
- PAR ID:
- 10398261
- Date Published:
- Journal Name:
- Proceedings of the International Symposium on Diagnostics and Modeling of Combustion in Internal Combustion Engines
- ISSN:
- 2424-2918
- Page Range / eLocation ID:
- 106-116
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1299/jmsesdm.2022.10.A7-4
