# Mining Contract: Modeling Natural Gas Explosions for Coal Mine Safety

Keywords:Coal miningComputer simulationExplosionsFire and explosion preventionNatural gasNumerical modelingTunnels

| Contract #                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   | 08FED898342 |
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| 1/1/2008                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| 9/30/2010                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
| This contract will simulate the development and evolution of natural gas (NG) explosions in mine tunnels. By performing a series of simulations using advanced numerical models and state-of-the-art computational technology, U.S. Naval Research Laboratory (NRL) researchers plan to answer questions such as:
- How do mine layout and the presence of turbulence generators, such as rough tunnel walls, tunnel supports, and other obstructions in tunnels, affect explosion pressure and the intensity of shocks?
- Can we quantify how the run-up distance to deflagration-to-detonation transition (DDT) changes with composition of NG?
- Can we determine any useful scaling between explosion parameters and obstacle size and spacing?
- What kind of pressure-time histories exist at various points in a NG explosion?
- What is the pressure-time history for various explosive gas cloud sizes behind a seal?
- What are run-up lengths for DDT for the different conditions studied?
- What range (variation) in the results of an explosion can we expect due to the stochastic nature of the processes involved?
- Can we determine any placement of obstructions or seals that would minimize or arrest DDT?
- What do the results of these studies suggest for the strength of seals?

NRL seeks the answers to questions concerning whether and how a NG mixture can detonate, whether the currently recommended 50-m criterion suggested for the transition to a detonation is conservative enough, whether a relatively small 5-m NG cloud can develop any significant pressures when ignited, and the effects of inhomogeneities in the gas cloud. |
| - Explosion Prevention                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |

## Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

NRL completed a simplified model describing thermodynamic, chemical, and diffusive properties of a stoichiometric CH4-air mixture. The model was calibrated using experimental properties of detonation waves and laminar flames in this mixture. To validate this model, NRL performed numerical simulations of flame acceleration and deflagration-to-detonation transition (DDT) in channels with obstacles. Researchers considered two channel widths, 17.4 and 52.0 cm, and two blockage ratios, 0.3 and 0.6, that correspond to reported experimental configurations used by Kuznetsov et al. (2002). For all four cases, the flame velocities as functions of distance from the ignition point and the distances to DDT show good agreement with experimental data.

Detonations originated from hot spots created by interactions of strong shocks with obstacles in a way similar to that observed in some experiments. NRL performed calculations for lean and rich methane-air mixtures, which showed that such mixtures would undergo smooth flame acceleration to a choking regime, but would not undergo DDT. NRL also performed calculations with inhomogeneous methane-air mixtures and conclusions are pending. The NRL simulations showed how shock waves interact and form the detonation cell structure in methane-air mixtures. The width of measured detonation cells at the NIOSH Lake Lynn Laboratory explosion tube match those inferred from the calculations. A final report describing all work performed by the NRL is in progress and will be completed by October 2010.

Research under this project resulted in the following publications:
        - Simulation of Deflagration-to-Detonation Transition in Premixed Methane-Air in Large- Scale Channels with Obstacles   D. Kessler, V. Gamezo and E. Oran, AIAA Paper AIAA-2009-0439 presented at the AIAA Aerospace Sciences Meeting, Orlando FL January, 2009.
        - DDT of Methane-Air Mixtures in a Channel with Obstacles   D.A. Kessler, V.N. Gamezo, and E.S. Oran, Poster paper presented at 32nd International Symposium on Combustion, Montreal Canada, August 2008.
        - New Detonation Facility for Simulating Methane-Air Explosions in Underground Coal Mines   R.K. Zipf, V.N. Gamezo, S. Harteis, E.S. Weiss, and E.S. Oran, Poster paper presented at 32nd International Symposium on Combustion, Montreal Canada, August 2008.
        - Non-Kolmogorov Turbulence Generation for Flame-Turbulence Interaction Studies   A.Y. Poludnenko, V.N. Gamezo, and E.S. Oran, Work in Progress, 32nd International Symposium on Combustion, Montreal Canada, August 2008.
        - Flame Acceleration and Deflagration-to-Detonation Transitions of Stoichiometric, Lean, and Rich Methane-Air Mixtures in Obstructed Channels   D. Kessler, V. Gamezo and E. Oran, presented and published at the 6th U.S. National Combustion Meeting, May 2009.
        - Multilevel Detonation Cell Structures in Methane-Air Mixtures   D. Kessler, V. Gamezo and E. Oran, Combustion and Flame, accepted, 2010.

### References

Kuznetsov M., Ciccarelli G., Dorofeev S., Alekseev V., Yankin Y., & Kim T.H. (2002). DDT in methane-air mixtures. *Shock Waves*, Vol. 12, pp. 215-220.

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          - A Centennial of Mine Explosion Prevention Research
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July 19, 2016

July 19, 2016

National Institute for Occupational Safety and HealthMining Program

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