21-40-01
99M90
Page: 2-2
Issued: May 9, 2012
Rev. New
I-Series Combustion Heater
Owners Manual
DESCRIPTION
2.1
Component Operation
Spark Spray Ignition
The controlled atomized spray from a specially designed spray nozzle, coupled with
high voltage spark plug ignition, ensures instant firing and continuous burning under
all flight conditions. Spark spray ignition combined with the exclusive HET whirling
flame combustion has been proved by millions of hours of heater operation in all types
of aircraft throughout the world.
Heat is produced by burning a fuel air mixture in the combustion chamber of the
heater. Aviation fuel is injected into the combustion chamber through the spray nozzle.
The resulting cone shaped fuel spray mixes with combustion air and is ignited by a
spark from the spark plug. Electric current for ignition is supplied by an ignition unit
which converts 12 volts or 24 volts to high voltage, oscillating current, to provide a
continuous spark across the spark gap. A shielded, high voltage lead connects the
ignition assembly to the spark plug. Combustion air enters the combustion chamber
tangent to its surface and imparts a whirling or spinning action to the air. This produces
a whirling flame that is stable and sustains combustion under the most adverse
conditions because it is whirled around itself many times. Therefore, ignition is continuous
and the combustion process is self piloting. The burning gases travel the length of the
combustion tube, flow around the outside of the inner tube, pass through cross over
passages into an outer radiating area, then travel the length of this surface and out the
exhaust. (See Figure 2.2)
Ventilating air passes through the heater between the jacket and combustion tube
assembly outer surface and through an inner passage in the assembly. Consequently
ventilating air comes into contact with two or more heated, cylindrical surfaces.
Fig. 2.2
Whirling Flame Depiction
