(47cj) The Effect of Non-Uniform Distribution of Obstacles on Deflagration-to-Detonation Transition (DDT)

The effect of non-uniform distribution of obstacles on

Deflagration-to-Detonation Transition (DDT)

 Camilo Rosas^{1, 2}, Hao Chen^{1, 2}, Eric Petersen ³, and M. Sam Mannan^{1, 2}*

¹ Mary Kay O’Connor Process Safety Center

² Artie McFerrin Department of Chemical Engineering

³ Department of Mechanical Engineering

Texas A&M University, College Station, Texas 77843-3122

The mechanisms for explosions are usually classified as two different types. The first mechanism is deflagration, a sub-sonic combustion wave with respect to the unburned gas ahead of the flame, during which the flame front and the shock front can be distinguished. The second type is detonation, which is a supersonic combustion wave propagating at 1500-2000m/s in fuel-air and can produce overpressures up to around 2 MPa. To obtain a detonation there are two different approaches. The first way is by direct initiation with a high energy source, and the second one is by inducing a transition from deflagration to detonation (DDT) with a low energy source and turbulence enhancers, which are also known as obstacles.

From previous research, the obstacles’ shape, distribution, and blockage ratio along the tube were always designed to be uniform. However, these designs deviate from real processes. For instance, different layouts of obstacles (e.g. pipe racks, turbines, and vessels) are substantially present in any facility, which could either accelerate and lead to DDT or quench the combustion process. Thus, in this work, the obstacles were designed to be distributed non-uniformly along the detonation tube to determine the effect of the randomness in the obstacles on the distance necessary to obtain DDT. Details of these experiments and the results are presented in the paper.

Computational Fluid Dynamics (CFD) models were also applied in this work to better understand the mechanisms. Even though CFD models do not represent DDT, various models are still able to predict high pressure values which are typically in the range of detonation pressures. Moreover, a CFD model capable of predicting the explosion behavior is of particular interest for the situation that the flame front captures the pressure front by the spatial pressure gradients across the flame front, which is one of the main mechanisms that may initiate a DDT.