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The project aims to tackle the extremely complex problem of flame acceleration, the conditions for transition from turbulent deflagration to detonation and detonation. These physical phenomena are highly multidisciplinary which involve fluid mechanics, combustion, shock dynamics and detonation. We will start with small scales for model development and validation. In such analysis advanced combustion models for flame acceleration will be coupled with detailed chemistry together with special measures to tackle the stiffness issues associated with the chemistry. On this basis, modelling techniques will be developed for large scale problems using simplified chemistry.
The research in return phase aims to pre-assigned return phase tasks by host professor Jennifer Wen, some evident achievements have been reached in 2013.7-2014.7 e.g. delivering a research seminar based on the incoming work, continuing on flame acceleration and detonation simulations, developing the flame acceleration and detonation experiments, initiating three PhD projects at detonation modeling studies, carrying out LNG dispersion, fire and explosions, submitting two proposals to National Natural Science Foundation of China, and publishing 5 Journal papers and 2 conference papers. The details can be generalized as follows.
(1) The researcher Dr Changjian Wang delivered a research seminar to the teachers and students at State Key Laboratory of Fire Science in University of Science and Technology of China. In this seminar, Dr. Wang presented the incoming work and EU IIF project progress, especially some excellent approaches .e.g. Method for Single-step chemistry model and transport coefficient model, Method for producing low-temperature thermo-data, the development of DDT solver, simulation of laminar flame interaction with porous media, simulation of DDT in the obstructed channel, simulation of large-scale outward-propagating detonation interaction with obstacles and etc.
(2) Mach reflection of gaseous detonation in a stoichiometric hydrogen-oxygen mixture diluted by 25 % argon was numerically studied using reactive Navier–Stokes equations and an eight-species, forty-eight-reaction mechanism. It was found that a Mach reflection mode always occurs for a planar detonation wave or planar air shock wave sweeping over wedges with apex angles ranging from 5 to 50 degree. The stochastic nature of boundary shape and transition distance, during deflagration-to-detonation transition, leads to relative disorder of detonation cell location and cell shape.
(3) A density-based solver for flame acceleration and deflagration-to-detonation transition were newly developed. The experiments conducted by Vollmer et al. (2011,2012) and Boeck et al. (2014a,2014b) were employed to validate current solver. The DDT cases were simulated in a channel with or without hydrogen concentration gradients. The simulation results demonstrate good quantitative agreement with experimental measurements in flame tip position, speed and pressure profiles, and moreover reproduce flame acceleration and DDT phenomena observed in the experiment. This show that the current solver performs well for modelling flame acceleration and DDT in homogeneous/inhomogeneous hydrogen-air mixture. Currently this solver has been applied in China to evaluate industrial explosion hazards.
(4) The experiments on flame acceleration and DDT were carried out in a tube obstructed with the soft sponge. A combustion tube with the length 1m and cross section 70mm×70mm were set up. The schlieren system was employed for optical visualization of the flame evolution and sponge deformation etc. 4 PCB transducers were mounted on the side wall for pressure histories. The effect of the blockage ratio on flame acceleration ratio was analyzed. The critical conditions for sponge deformation and cutoff were obtained. Some phenomena such as shock evolution at the sponge corner, shear layer with vortex, sponge pyrolysis or ignition etc were together discussed. This work extended the scope of explosion science because previous work mainly focused on the flame interaction with rigid obstacles.
(5) Numerical simulation of LNG dispersion, fire and explosions were performed. According to the method of producing low-temperature thermo-data, the NG gas thermo-data between 110.67K and 200K were obtained. Especially some models were developed for LNG fire simulations in OpenFOAM toolbox, such as multi-component based EDC model, EDC-based soot model, PaSR-based soot model, WSGGM radiation model etc. Some of these models has been adopted by FM Global and applied in fireFoam solver.
(6) A Model Evaluation Protocol (MEP) for vapour cloud detonation studies was finished. We extensively studied the effects of numerical schemes in OpenFOAM, Courant number, proposed chemistry model, flame acceleration model etc. on DDT or detoantion. It should be suggested that the 2nd-order Crank Nicholson scheme for time, 2th-order Vanleer, TVD, MUSCL for divScheme and Gauss MUSCL phi corrected for Laplacian Scheme be well approachable. Additionally Courant number for detonation simulations should be less than 0.1 for more resolution under a coarser mesh. The one-step chemistry model and corresponding thermo data are also favorable in large-scale simulation.
(7) Both Dr. Wang and I initialized three PhD projects at detonation modeling studies. The first one is flame acceleration and DDT in a channel with hydrogen concentration gradients. The second is flame acceleration and DDT in a channel with moving boundary. The last one is non-uniform hydrogen-air mixture detonation in a semi-confined flat layer. These projects have potential applications in preventing and alleviating the hazards in hydrogen storage, use and transportation etc in China.
(8) Based on above work, we submitted two proposals to National Natural Science Foundation of China. One is study of combustible gas explosion with concentration gradients. The other is study of liquid fuel vapor explosion suppression by water mist in an enclosed compartment. In addition, we also submitted a proposal on low-temperature thermo-data to Chinese Academy of Sciences and got the funding.
(9) During the project, we published 5 Journal papers and 2 conference papers (Please see the publication list). Wherein, 4 Journal papers are Science-cited.