An early method of atomizing the fuel is to pass it
through a swirl chamber where tangentially disposed holes
or slots imparted swirl to the fuel by converting its pressure
energy to kinetic energy. In this state, the fuel is passed
through the discharge orifice that removes the swirl motion
as the fuel is atomized to form a cone-shaped spray. This is
called “pressure jet atomization.” The rate of swirl and
pressure of the fuel at the fuel spray nozzle are important
factors in good atomization. The shape of the spray is an
indication of the degree of atomization as shown in
Figure 7e15. Later fuel spray nozzles utilize the airspray
principle that employs high velocity air instead of high
velocity fuel to cause atomization. This method allows
atomization at low fuel flow rates (provided sufficient air
velocity exists) thus providing an advantage over the
pressure jet atomizer by allowing fuel pumps of a lighter
construction to be used.