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# The Effect of Initial Temperature on Flame Acceleration and Deflagration-to-Detonation Transition Phenomenon (NUREG/CR-6509, BNL-NUREG-52515)

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## Publication Information

**Manuscript Completed:**April 1998**Date Published:**May 1998

**Prepared by:** G. Ciccarelli, J.L. Boccio, T. Ginsberg, C. Finfrock, L. Gerlach Brookhaven National Laboratory Upton, New York 11973-5000

H. Tagawa Nuclear Power Engineering Corporation 5F Fujita Kanko Toranomon Building 3-17-1, Toranomon, Minato-Ku Tokyo 105, Japan

A. Malliakos, NRC Project Manager

**Prepared for:**Division of Systems Technology Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission ****Washington, DC 20555-0001

and

Nuclear Power Engineering Corporation 5F Fujita Kanko Toranomon Building 3-17-1, Toranomon, Minato-Ku Tokyo 105, Japan

NRC FIN L-1924, A-3991 

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## Abstract

The High-Temperature Combustion Facility at BNL was used to conduct deflagration-to-detonation transition (DOT) experiments. Periodic orifice plates were installed inside the entire length of the detonation tube in order to promote flame acceleration. The orifice plates are 27.3-cm-outer diameter, which is equivalent to the inner diameter of the tube, and 20.6-cm-inner diameter. The detonation tube length is 21.3-meters long, and the spacing of the orifice plates is one tube diameter. A standard automobile diesel engine glow plug was used to ignite the test mixture at one end of the tube. Hydrogen-air-steam mixtures were tested at a range of temperatures up to 650K and at an initial pressure of 0.1 MPa.

In most cases, the limiting hydrogen mole fraction which resulted in DOT corresponded to the mixture whose detonation cell size, *λ,*was equal to the inner diameter of the orifice plate, d (e.g., d/λ=1). The only exception was in the dry hydrogen-air mixtures at 650K where the DOT limit was observed to be 11 percent hydrogen, corresponding to a value of d/λ equal to 5.5. For a 10.5 percent hydrogen mixture at 650K, the flame accelerated to a maximum velocity of about 120 m/s and then decelerated to below 2 m/s. By maintaining the first 6.1 meters of the vessel at the ignition end at 400K, and the rest of the vessel .at 650K, the DOT limit was reduced to 9.5 percent hydrogen (d/λ=4.2). This observation indicates that the d/λ=1 DOT limit criteria provides a necessary condition but not a sufficient one for the onset of DOT in obstacle laden ducts. In this particular case, the mixture initial condition (i.e., temperature) resulted in the inability of the mixture to sustain flame acceleration to the point where DOT could occur.

It was also observed that the distance required for the flame to accelerate to the point of detonation initiation, referred to as the run-up distance, was found to be a function of both the hydrogen mole fraction and the mixture initial temperature. Decreasing the hydrogen mole fraction or increasing the initial mixture temperature resulted in longer run-up distances. The density ratio across the flame and the speed of sound in the unburned mixture were found to be two parameters which influence the run-up distance.

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