he burner.
Early experiments with these air distributors were confined largely to
single or duplicate cones used with the idea of directing the air to the
axis of the burner. A highly successful method of such air introduction,
developed by Messrs. Peabody and Irish of The Babcock & Wilcox Co., is
by means of what they term an "impeller plate". This consists of a
circular metal disk with an opening at the center for the oil burner and
with radial metal strips from the center to the periphery turned at an
angle which in the later designs may be altered to give the air supply
demanded by the rate of combustion.

The air so admitted does not necessarily require a whirling motion, but
experiments show that where the air is brought into contact with the oil
spray with the right "twist", better combustion is secured and lower air
pressures and less refinement of adjustment of individual burners are
required.

Mechanical burners have a distinct advantage over those in which steam
is used as the atomizing agent in that they lend themselves more readily
to adjustment under wider variations of load. For a given horse power
there will ordinarily be installed a much greater number of mechanical
than steam atomizing burners. This in itself is a means to better
regulation, for with the steam atomizing burner, if one of a number is
shut off, there is a marked decrease in efficiency. This is due to the
fact that with the air admitted under the burner, it is ordinarily
passing through the checkerwork regardless of whether it is being
utilized for combustion or not. With a mechanical burner, on the other
hand, where individual burners are shut off, air that would be admitted
for such burner, were it in operation, may also be shut off and there
will be no undue loss from excess air.

Further adjustment to meet load conditions is possible by a change in
the oil pressure acting on all burners at once. A good burner will
atomize moderately heavy oil with an oil pressure as low as 30 pounds
per square inch and from that point up to 200 pounds or above. The
heating of the oil also has an effect on the capacity of individual
burners and in this way a third method of adjustment is given. Under
working conditions, the oil pressure remaining constant, the capacity of
each burner will decrease as the temperature of the oil is increased
though at low temperatures the reverse is the case. Some experiments
with a Texas crude oil having a flash poin