Piper Navajo PA-31 Service Manual page 917

381 A
HIGH VELOCITY
WHIRLING FLAME
SPARK PLUG
/ COMBUSTION AIR
HEATED AIR
VALVE
EXHAUST GASES
FRESH AIR
FROM BLOWER
Figure 13-6. Cutaway of Heater, Showing Whirling Flame (Typical)
13-6. DESCRIPTION OF HEATER AND BASIC COMPONENTS.
13-7. SPARK-SPRAY IGNITION. (Refer to Figure 13-6Z.) The controlled atomized spray from a specially
designed spray nozzle, coupled with high-voltage spark plug ignition, insures instant firing and continuous
burning under all flight conditions.
Heat is produced by burning a fuel-air mixture in the combustion chamber of the heater. Aviation
gasoline 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 28-volts to high-voltage, oscillating current to provide a
continuous spark across the spark plug 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.
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.
13-8. FUEL REGULATOR AND SHUTOFF VALVE. (Refer to Figure 13-7.) This unit provides preset,
regulated fuel pressure as well as remote shut-off to the heater, regardless of fuel inlet pressure variations. It
is set at 7 psi, with inlet pressures up to 50 psi. The shutoff valve is operated by a solenoid and is adjustable,
but not repairable.
Reissued: 10/12/79
HEATING AND VENTILATING SYSTEM
PIPER NAVAJO SERVICE MANUAL
5B11