General Requirements for a burner
 Mixture of fuel with primary air
should be within the limits of
inflammability
 Flame stability should be maintained
throughout the combustion
 All factors causing flame extinction
and flash back should be avoided

General Requirements for a burner
 Adequate combustion space should be
provided for its completion
 Complete mixing of oxygen and fuel is
desirable( may be obtained by creating
turbulence in the combustion space)
 Flame shape should correspond to the
geometry of furnace

Burner Selection
 Flame Shape
 Combustion Volume
 Stability
 Drive
 Turndown Ratio:
Ratio of maximum to minimum heat input rates within
which burner operates satisfactorily
Maximum limit depends upon flame blow off. Minimum limit
depends upon flame flash back

Simple Burner
Fuel
Air
Burning Velocity
Flow velocity
• Burning Velocity > Flow Velocity : Flash Back Limit
• Burning Velocity < flow Velocity : Blow Off Limit
• Burning Velocity = Flow Velocity : Stable Flame.
• The ability of the
combustion process to
sustain itself in a
continuous manner is
called Combustion
Stability.
• Stable and efficient
combustion can be
upset by too lean or
too rich mixture.

Burners for Liquid Fuels
The purpose of a fuel burning system are to
 To position flame at areas of useful heat
release
 Initiate and maintain ignition
 Mix the fuel and air
 Volatilize the fuel
 Proportion the fuel to air

Schematic of an Industrial Combustion Process

Liquid Fuel Burners
Oils may be burnt in two ways
 it is vaporized before ignition so that
it burns like a gas
(vaporising burners)
 it is converted into droplets which are
injected into hot air so that they
evaporate while burning (atomising
burners)

Liquid Fuel Burners
Atomising burners: On industrial scale, most
commonly used burners are atomising
burners
 Oil is heated to low viscosity and atomised
(i) Mechanically by means of a rotating disc
or cup with a uniform droplet size (50
microns)
(ii) By a high pressure ejection from a fine
orifice which gives a conical spray

Liquid Fuel Burners
 by an entrainment in a blast of air or
steam
 air atomisation gives a better
theoretical flame temperature as
compared to steam
 steam atomisation is preferred for
high viscosity fuels to reduce the
viscosity e.g. for residual fuel oils

Liquid Fuel Burners
 For most of the applications
compressed air is the atomising
fluid
 The minimum temperature at which
an oil is pumpable in practice
depends upon the viscosity of the oil