Flashpoint,Firepoint and spontaneous ignition

the liquid temperature at which application of an ignition source will cause a flame to flash across the surface of the liquid. the flame will NOT be sustained

the lowest temperature at which the rate of supply of fuel vapours (by evaporation) can sustain the flame

This is the lowest temperature at which the substance will ignite spontaneously, that is the substance will burn without the application of a flame or other ignition source. This is sometimes referred to as the auto-ignition temperature

Once a flame has been established and flammable vapours are rising from the fuel surface, heat and what are called chain carriers are produced where the flame reactions are occurring. A proportion of these will pass into the next layer of gas and start the oxidation and heat release processes there, rather as in a relay race. Chain carriers are believed to be atoms or fragments of molecules known as free radicals which are extremely reactive

Chain carriers are believed to be atoms or fragments of molecules known as free radicals which are extremely reactive

laminar flow and turbulant flow

is steady flow in which two particles starting at any given point follow the same path. Particles never cross each other’s paths, so the particle paths are bunched together like uncooked spaghetti in a packet. At any given time, the velocities of all particles on one path are the same, but the velocities of particles in different paths might be different. Laminar flow is associated with slow flow over smooth surfaces.

there are random changes in velocity and direction of the flow, although the flow as a whole is moving in a definite direction. If we consider wind blowing down a street on a windy day, leaves and litter may be blown up, down, across and around, revealing local changes in the flow, but the general direction of the wind is still down the street. Turbulent flow tends to occur in fast flows over rough surfaces and around obstacles.

occur when a fuel is well-mixed with an oxidant, e.g., 10% methane mixed with air. For ignition to occur, energy must be supplied to the system in the form of a spark or small flame. A self-sustaining flame will then be established around the ignition source and propagate outwards in all directions.

pressure, temperature, dimensions of the test apparatus, direction of flame propagation and moisture content of the mixture all have some effect. (In general, the limits widen with rise in temperature.)

optimum mixture in which there is just sufficient fuel to use up all the oxygen.

For each mixture of fuel and air between the flammability limits, there is a characteristic burning velocity at which a premixed flame will propagate through a stationary gas

Diffusion flames occur at the interface where fuel vapour and air meet. Unlike premixed flames, the fuel vapour and the oxidant are separate prior to burning.