A fuel injection system is considered to be less susceptible to
icing than the carburetor system, but impact icing on the air
intake is a possibility in either system. Impact icing occurs
when ice forms on the exterior of the aircraft, and blocks
openings such as the air intake for the injection system.
Advantages of fuel injection:
• Reduction in evaporative icing
• Better fuel flow
• Faster throttle response
• Precise control of mixture
• Better fuel distribution
• Easier cold weather starts
Disadvantages:
• Difficulty in starting a hot engine
• Vapor locks during ground operations on hot days
• Problems associated with restarting an engine that
quits because of fuel starvation |
Superchargers and Turbosuperchargers
To increase an engine's horsepower, manufacturers have
developed forced induction systems called supercharger
and turbosupercharger systems. They both compress the
intake air to increase its density. The key difference lies in
the power supply. A supercharger relies on an engine-driven
air pump or compressor, while a turbocharger gets its power
from the exhaust stream that runs through a turbine, which in
turn spins the compressor. Aircraft with these systems have
a manifold pressure gauge, which displays MAP within the
engine's intake manifold.
On a standard day at sea level with the engine shut down,
the manifold pressure gauge will indicate the ambient
absolute air pressure of 29.92 "Hg. Because atmospheric
pressure decreases approximately 1 "Hg per 1,000 feet of
altitude increase, the manifold pressure gauge will indicate
approximately 24.92 "Hg at an airport that is 5,000 feet above
sea level with standard day conditions.
As a normally aspirated aircraft climbs, it eventually reaches
an altitude where the MAP is insufficient for a normal climb.
That altitude limit is the aircraft's service ceiling, and it is
directly affected by the engine's ability to produce power.
If the induction air entering the engine is pressurized, or
boosted, by either a supercharger or a turbosupercharger,
the aircraft's service ceiling can be increased. With these
systems, an aircraft can fly at higher altitudes with the
advantage of higher true airspeeds and the increased ability
to circumnavigate adverse weather. |