COMBUSTION FUNDAMENTALS: CHARACTERISTICS OF COMBUSTION PROCESSES
Referring to the reaction rate equation, there are two factors
which dictate whether combustion takes place. That is for the
system to be transformed from a stable mixture to a rapidly
reacting combustion process. The first is that there should be
sufficient energy to allow initiation of the reaction. This may
be supplied by any of a number of methods: electrical spark,
heat addition, radical addition. The propensity of a system to
burn is dependent on many factors: fuel type, calorific value,
mixture, pressure, velocity, turbulence, enclosure geometry. SIT
may be characterised in some way by the Spontaneous Ignition
temperature. This is defined as the temperature above which
combustion, once initiated, will maintain itself and below which
active combustion cannot occur. This is tabulated in table I for
some common fuels. If heat is conducted away sufficiently
rapidly, the temperature may be reduced below the ignition point
and combustion ceases