Unconfined vapor cloud explosion
Encyclopedia
Gas explosions can generate overpressure
without the presence of confining walls. This is referred to as Unconfined Vapor Cloud Explosions (UVCEs). If a flame travels through the unconfined gas cloud with high velocity, the gas/air mixture ahead of the flame is unable to move away quickly enough to allow free expansion of the combustion products formed by the flame. As a result pressure wave is formed ahead of the flame front. The presence of obstacles (called congestion) within the flow field of the gas cloud produces turbulence which enhances the burning velocity, accelerates the production of combustion products and increases the flame speed. The higher the velocity of the flame, the higher the pressure generated ahead of it. If very high flame speeds are produced, a Transition from Deflagration to Detonation (DDT) can occur.
In simple terms, a detonation involves a very high pressure shock wave
that auto-ignites the gas/air mixture. The combustion of this mixture then provides the energy to sustain the shock wave. As a result, a detonation is self-sustaining as long as the concentration of gas is within certain limits.
Overpressure
The term Overpressure is applied to a pressure difference, relative to a "normal" or "ambient" pressure, in various circumstances:* In engineering: the pressure difference over the wall thickness of a pressure vessel...
without the presence of confining walls. This is referred to as Unconfined Vapor Cloud Explosions (UVCEs). If a flame travels through the unconfined gas cloud with high velocity, the gas/air mixture ahead of the flame is unable to move away quickly enough to allow free expansion of the combustion products formed by the flame. As a result pressure wave is formed ahead of the flame front. The presence of obstacles (called congestion) within the flow field of the gas cloud produces turbulence which enhances the burning velocity, accelerates the production of combustion products and increases the flame speed. The higher the velocity of the flame, the higher the pressure generated ahead of it. If very high flame speeds are produced, a Transition from Deflagration to Detonation (DDT) can occur.
In simple terms, a detonation involves a very high pressure shock wave
Shock wave
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium or in some cases in the absence of a material medium, through a field such as the electromagnetic field...
that auto-ignites the gas/air mixture. The combustion of this mixture then provides the energy to sustain the shock wave. As a result, a detonation is self-sustaining as long as the concentration of gas is within certain limits.