Aircraft Systems

After reaching the fuel manifold valve, the fuel is distributed or boosted, by either a supercharger or a turbosupercharger, to the individual fuel discharge nozzles. The discharge the aircraft’s service ceiling can be increased. With these nozzles, which are located in each cylinder head, inject the systems, an aircraft can fly at higher altitudes with the fuel-air mixture directly into each cylinder intake port. advantage of higher true airspeeds and the increased ability to circumnavigate adverse weather. A fuel injection system is considered to be less susceptible to icing than a carburetor system, but impact icing on the air Superchargers intake is a possibility in either system. Impact icing occurs A supercharger is an engine-driven air pump or compressor when ice forms on the exterior of the aircraft and blocks that provides compressed air to the engine to provide openings, such as the air intake for the injection system. additional pressure to the induction air so that the engine can produce additional power. It increases manifold pressure and The following are advantages of using fuel injection: forces the fuel-air mixture into the cylinders. Higher manifold pressure increases the density of the fuel-air mixture and • Reduction in evaporative icing increases the power an engine can produce. With a normally • Better fuel flow aspirated engine, it is not possible to have manifold pressure • Faster throttle response higher than the existing atmospheric pressure. A supercharger is capable of boosting manifold pressure above 30 "Hg. • Precise control of mixture • Better fuel distribution For example, at 8,000 feet, a typical engine may be able to • Easier cold weather starts produce 75 percent of the power it could produce at mean sea level (MSL) because the air is less dense at the higher altitude. The supercharger compresses the air to a higher The following are disadvantages of using fuel injection: density allowing a supercharged engine to produce the same • Difficulty in starting a hot engine manifold pressure at higher altitudes as it could produce • Vapor locks during ground operations on hot days at sea level. Thus, an engine at 8,000 feet MSL could still produce 25 "Hg of manifold pressure whereas, without a • Problems associated with restarting an engine that supercharger, it could only produce 22 "Hg. Superchargers quits because of fuel starvation are especially valuable at high altitudes (such as 18,000 feet) where the air density is 50 percent that of sea level. The use Superchargers and Turbosuperchargers of a supercharger in many cases will supply air to the engine To increase an engine’s horsepower, manufacturers have at the same density it did at sea level. developed forced induction systems called supercharger and turbosupercharger systems. They both compress the The components in a supercharged induction system are similar intake air to increase its density. The key difference lies in to those in a normally aspirated system, with the addition of the power supply. A supercharger relies on an engine-driven a supercharger between the fuel metering device and intake air pump or compressor, while a turbocharger gets its power manifold. A supercharger is driven by the engine through a from the exhaust stream that runs through a turbine, which in gear train at one speed, two speeds, or variable speeds. In turn spins the compressor. Aircraft with these systems have addition, superchargers can have one or more stages. Each a manifold pressure gauge, which displays MAP within the stage also provides an increase in pressure and superchargers engine’s intake manifold. may be classified as single stage, two stage, or multistage, depending on the number of times compression occurs. On a standard day at sea level with the engine shut down, the manifold pressure gauge indicates the ambient An early version of a single-stage, single-speed supercharger absolute air pressure of 29.92 "Hg. Because atmospheric may be referred to as a sea-level supercharger. An engine pressure decreases approximately 1 "Hg per 1,000 feet of equipped with this type of supercharger is called a sea-level altitude increase, the manifold pressure gauge indicates engine. With this type of supercharger, a single gear-driven approximately 24.92 "Hg at an airport that is 5,000 feet above impeller is used to increase the power produced by an engine sea level with standard day conditions. at all altitudes. The drawback with this type of supercharger is a decrease in engine power output with an increase in altitude. As a normally aspirated aircraft climbs, it eventually reaches an altitude where the MAP is insufficient for a normal climb. Single-stage, single-speed superchargers are found on many This altitude limit is known as the aircraft’s service ceiling, high-powered radial engines and use an air intake that faces and it is directly affected by the engine’s ability to produce forward so the induction system can take full advantage of power. If the induction air entering the engine is pressurized, 7-12