the outer shell of the nozzle and passes through the secondary screen
and into the secondary swirl slots. The secondary swirl slots, being
slightly larger in size than the primary swirl slots, allow a greater
volume of fuel to be discharged into the combustor. The combination
of primary and secondary flow which is delivered to the combustor at
anoptimum spray angle of 90 is sufficient to operate the engine at
all power settings above 32% N1.
To further atomize the fuel entering the combustor liner,
swirl cones located at the aft end of the combustor liner assembly
allow combustion air to enter the liner and swirl in the opposite
direction to that of the fuel being injected by the atomizer. This
additional swirling air establishes a definite flame pattern at the
end of each atomizer. Additionally, air is routed through the air
shroud to cool the atomizers and assist in establishing this flame
pattern. When fuel flow is cut off at engine shutdown, the inlet
pressure falls below the dumpvalve opening pressure, and the dump
valve plunger is moved by its spring to the fully open position. The
fuel in the primary manifold then flows to drain through the main
flow passage between the flow divider and drain valve. The secondary
manifold is drained via a small drain port in the upper housing
leading into the dumpvalve cavity.
b. Manual fuel flow. The manual or emergency fuel flow
sequence is the same as normal fuel flow sequence except for the
fuelcontrol changeover valve. When the changeover valve is actuated
to the manual position, fuel is redirected to the manualsystem
metering valve, which is mechanically linked to the main power
control in the cockpit. This flow path bypasses the main metering
valve. Other than that, the manual fuelflow sequence is the same as
the normal. The fuel system on the T53L13 is similar to the one on
the T53L701. However, the T53L701 turboprop engine has a fuel
heater to prevent fuel from icing by using engine lubricating oil to
heat the fuel. The fuel heater supplies fuel in temperature ranges
between 35 to 70 F when fuel inlet temperatures are in the 65 to
70 F range.
4.16.
INTERNAL COOLING AND PRESSURIZATION SYSTEM
The internal cooling system provides cooling air to the
internal engine components and pressurizes the number one, two, and
three main bearing seals. Cooling and pressurization air is obtained
from five parts of the engine. The following numbers in parentheses,
such as (1), (2), and so on in the discussion, correspond to similar
numbers in figure 4.24 and refer you to that particular portion of
the engine. Air flows down through the fourth stage spacer (1) into
the
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