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Content archived on 2024-04-15

INVESTIGATION OF FLAME PROPAGATION INFLUENCE OF REPEATED OBSTACLES AND PARTIAL CONFINEMENT

Objective

THE EXPERIMENT WILL REVEAL IMPORTANTS DATA IN THE INFLUENCE OF OBSTACLE PARAMETERS AND OBSTACLE ARRANGEMENTS IN TWO DIFFERENT MODES OF FLAME PROPAGATION AND FOR VARIOUS REACTIVITIES OF GASES.
Vapour cloud explosions have proved to be potentially devastating. Incidents as in Flixborough and Beek have shown the need to assess the risk of vapour cloud explosions. Gas explosion research during the last decade shows that a fuel-air mixture is explosive only under appropriate boundary conditions, ie only where the mixture is partially confined and/or obstructed.

In general the initial stage in the process of deflagrative combustion in gas explosions is more or less laminar, which is a slow process. However, slow laminar combustion can develop into an intense explosive and blast generating process, caused by the phenomenon of turbulence. The turbulence is caused by the influence of obstacles and/or confinements.

The effect of artificially produced turbulence on flame propagation has been investigated and an experimental parameter study into flame propagation in diverging and nondiverging flows obstructed by obstacles and partial confinement has been performed.
THE EMPHASIS WILL BE PLACED ON THE 1-DIMENSIONAL CHANNEL, WHICH WILL BE TYPICALLY 500 MM WIDE, 250 MM HIGH AND 2000 MM LONG. THE DIMENSIONS CAN BE VARIED. IN BOTH SET-UPS GAS MIXTURES WILL BE PREPARED AND IGNITED. IGNITION CAN BE RELATIVELY 'SOFT' USING A SPARK, OR 'STRONG' USING A FLAME JET. THE LATTER WILL BE PRODUCED BY A DRIVER TUBE AS AN EXTENSION OF THE SET-UP.IN THIS WAY IT IS POSSIBLE TO INSTALL AND INVESTIGATE BOTH FLAME PROPAGATION REGIMES.VERTICAL OBSTACLES WILL BE MOUNTED INSIDE THE SET-UPS. THE INFLUENCE WILL BE STUDIED OF VARIOUS OBSTACLE PARAMETERS, SUCH AS THE OBSTACLE ARRANGEMENT (PITCH, BLOCKAGE RATIO, STAGGERING), THE OBSTACLE DIAMETER (50 TO 200 MM, TYPICALLY 100 MM), THEIR SHAPE AND SURFACE ROUGHNESS.THE INFLUENCE OF THE REACTIVITY OF THE GAS MIXTURE WILL BE INVESTIGATED BY USING DIFFERENT GAS COMPOSITIONS AND BY USING TWO DIFFERENT GASES (PROPANE AND ETHYLENE). ETHYLENE WILL BE USED IN MOST OF THE TESTS. DETAILED RECORDING OF FLAME PROPAGATION IN BOTH SET-UPS WILL BE PERFORMED USING HIGH-SPEED CAMERAS (MAX. 10.000 FRAMES PER SECOND) MOUNTED ABOVE THE TRANSPARENT TOP PLATES. PRESSURE DEVELOPMENT INSIDE THE SET-UPS WILL BE RECORDED BY PRESSURE GAUGES. THE EXPERIMENTS WILL REVEAL IMPORTANT DATA ON THE INFLUENCE OF OBSTACLE PARAMETERS AND OBSTACLE ARRANGEMENTS IN TWO DIFFERENT MODES OF FLAME PROPAGATION AND VARIOUS REACTIVITIES OF GASES. EVALUATION OF THE TEST RESULTS SHOULD LEAD TO A BETTER UNDERSTANDING OF THE MECHANISM OF FLAME PROPAGATION NEAR OBSTACLES GIVING FIRST OPPORTUNITIES TO PREDICT MAXIMUM FLAME SPEEDS AND PRESSURE DEVELOPMENT IN ANY GIVEN OBSTACLE ENVIRONMENT AT AN ARBITRARY SCALE FOR VARIOUS GASES. THE RESULTS OF THE EXPERIMENTS PROPOSED BY PTB ON THE RELATION BETWEEN TURBULENCE AND TURBULENT FLAME PROPAGATION WILL BE USED IN THE INTERPRETATION OF THE EXPERIMENTS. IN ORDER TO USE THE DATA OBTAINED BY PTB ON THE TURBULENT FLAME VELOCITY, INFORMATION MUST BY AVAILABLE ON THE TURBULENT FLUCTUATION VELOCITY AND THE INTEGRAL LENGHT SCALE DURING THE EXPERIMENTS. SINCE THE EXPERIMENTS ARE NON-STEADY (IN CONTRAST WITH THE PTB-EXPERIMENTS), MEASUREMENT OF THESE QUANTITIES DURING THE EXPLOSION EXPERIMENTS IS VIRTUALLY IMPOSSIBLE. THEREFORE CALCULATIONS WILL BE MADE OF THE FLOW FIELD USING THE REACTIVE GASDYNAMIC COMPUTER CODE REAGAS DEVELOPED AT THE PRINS MAURITS LABORATORY TNO. TO THIS END THE CODE WILL BE VALIDATED FOR THIS TYPE OF USE USING PUBLISHED DATA AND A (LIMITED) NUMBER OF EXPERIMENTS. IN THESE EXPERIMENTS OBSTACLES AS USED IN THE EXPLOSION TESTS WILL BE PLACED IN A STEADY FLOW AND THE FLOW FIELD PARAMETERS BEHIND THE OBSTACLES MEASURED. THE CODE WILL THEN BE USED TO GENERATE INFORMATION ON THE NON-STEADY FLOW FIELD. FOR THE EVALUATION OF THE EXPLOSION EXPERIMENTS THE CODE REAGAS WILL BE USED AGAIN.

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Business Unit of TNO Built Environment and Geosciences
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Van Mourik Broekmanweg 6
2628 XE DELFT
Netherlands

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