Density controller and differential pressure controller system
 engine at increased throttle
for take-off. When the throttle is opened for take-off, the pressure
differential before and after the throttle valve is low. This small differential
on the controller diaphragm is inadequate to force the controller valve
completely off its seat. Thus the engine during climb at
full power. When the throttle valve is wide open, there's no pressure
differential between the two sides of the throttle valve. Therefore, the
differential pressure controller remains in the normally closed position.
Regulation of oil pressure, and by extension, regulation of turbocharger
operation, is controlled by the density controller. This controller is
designed to hold the air density constant at the injector entrance. The
density controller is designed with a pressure and temperature sensing
bellows that responds to changes of the temperature and pressure of the
air between the compressor and the fuel injector inlet. As this temperature
or pressure changes, the bellows expands or contracts, changing the position
of the metering valve in the controller and the oil pressure in the exhaust
bypass valve. Air temperature is significant because a higher manifold
pressure is required as air temperature increases. Higher manifold pressure
results in a greater temperature rise across the compressor. This is why
wide open throttle manifold pressure increases with either altitude or
outside air temperature. In a full throttle climb, there will usually be
3 to 4 inches between sea level and the point at which the exhaust bypass
valve butterfly is closed to its design maximum.
Engine cruising at altitude.
During cruise at part throttle operation, the density controller does not
control oil pressure. The valve in the density controller remains closed
and the oil pressure is controlled by the differential pressure controller.
When operating at part throttle, there's a significant air pressure differential
across the throttle valve. The high pressure above the diaphragm keeps
the metering valve in the differential pressure controller from fully closing,
thus permitting a controlled amount of bleed oil to the crankcase.
Thus, deck pressure cannot be too high.
|
