Powerplant

1
Lecture 2

• Powerplant
• and
• Other Systems (1)
• Chapter 2, Jeppesen

2
Powerplant Overview

• The Engine
• General engine construct and operation
• Fuel induction systems
• Carburetor
• Fuel injection
• The ignition system
• Abnormal combustion

3

• Airplane Engines
• General engine construct and operation

4
Two basic types of plane engines

• Turbine engine
• Also called jet engine
• Extremely powerful
• More costly
• Used in large passenger carriers
• Reciprocating engine
• Used with propellers
• Less powerful
• More economical
• Used in aviation training airplanes and other
  planes

5
Reciprocating Engine Operation

• The engine consists of several (e.g., 4) pistons
  each embedded in a cylinder
• Fuel-air mixture in the cylinder is compressed by
  the piston, then is ignited.
• The combustion explosion pushes the piston, which
  drives the propeller of the plane through a
  crankshaft.

6
Reciprocating Engine Operation (2)

• The engine operates in a so-called Four-Stroke
  Operating Cycle
• Fuel-air intake
• Compression
• Power
• Exhaust
• Fig. 2-22
• In a four-cylinder engine, at any moment, each
  cylinder operates at a different stroke. The
  four cylinders operate in a synchronized manner
  to maintain a continuous rotation of the
  crankshaft and the propeller. Timing is very
  important.

7
Reciprocating Engine Operation (3)

• The Four-Stroke Operating Cycle
• Fuel-air intake piston is drawn away from
  cylinder head, intake valve opens, fuel-air (f-a)
  mixture sucked into combustion chamber
• Compression piston moves back towards cylinder
  head, intake valve closed, f-a mixture compressed
• Power spark plugs fire, f-a mixture ignited and
  explode, providing the power to drive piston
  which rotates the crankshaft
• Exhaust piston goes back towards cylinder head,
  expels the burned gases from chamber through
  opened exhaust valve
• Fig. 2-22

8
The four-stroke operation cycle (2-22)
9

• The Induction Systems

10
Induction

• Induction means bring in outside air into the
  engine, mix it with fuel in the proper
  proportion, and deliver it to the cylinder where
  combustion occurs.
• Two controls are used to control the fuel and
  air, thus controlling the engine speed-
• The throttle is used to control the amount of
  fuel-air mixture that flows into the cylinders
• The mixture controls the ratio between fuel and
  air.

11
Carburetor (1)

• How is air mixed with the fuel? It is mixed in
  the carburetor (Fig 2-25)
• The Carburetor is a device consisting of a small
  fuel chamber and a cylinder constricted in the
  middle (the venturi )
• Air goes into the lower part of the carburetor
  cylinder into the venturi.
• Fuel is also delivered into the venturi to mix
  with the air.
• Fuel-air ratio is adjusted by the mixture control
  in the cockpit (through a mixture needle).

12
Float-type Carburetor used by many light plane
(2-25)
13
Carburetor (2)

• The fuel-air mixture then goes to the upper part
  of the carburetor cylinder, where it goes through
  a throttle valve and then to the combustion
  chambers of the engine cylinders to be burnt
• The throttle valve controls the rate of the flow
  of the f-a mixture by partially blocking the
  upper opening of the carburetor
• This throttle valve is controlled by the throttle
  in the cockpit

14
Carburetor (3) - Mixture

• Carburetors are calibrated at sea level for the
  right ratio of air and fuel mixture
• As altitude increases density of air decreases
  but fuel density remains unchanged, changing the
  f-a mixture ratio. You have to get the right
  ratio back using the mixture control
• As you descent you have to remember to re-adjust
  the mixture ratio again
• Process of mixture adjustment differs among
  planes, thus should refer to Pilots Operating
  Handbook often related to engine temperature

15
Carburetor Icing (1)

• Fuel vaporization in the venturi and decrease of
  air pressure there causes a sharp temperature
  drop in the carburetor
• If the air has a lot of water vapor the low
  temperature may cause ice to form inside the
  carburetor, including the throttle valve.
• This restricts the passage way to the engine and
  results in loss of power. (Fig. 2-26)
• This is especially dangerous when engine power is
  already set low, e.g., during descent.

16
Carburetor Icing (2-26)
17
Carburetor Icing (2)

• Carburetor icing is more likely to form when
  temperature gets below 21?C and relative humidity
  is above 80 (Fig 2-27)
• To fight carburetor ice planes with float-type
  carburetors use a carburetor heat control in the
  cockpit to divert some hot exhaust air into the
  carburetor for fuel-air mixture
• This causes a slight imbalance of fuel-air
  mixture as the heated air is less dense and it
  has been used. Thus re-adjustment of the ratio
  might be desirable.

18
Carburetor ice forms at temperatures below 21?C
and humidity above 80
19
Carburetor Icing (3)

• In a fixed-pitch propeller engine, if ice is
  present, carburetor heat will first result in a
  slight decrease of engine speed, followed by a
  gradual increase as the ice melts.
• If ice were not present, carburetor heat will
  first result in a slight decrease in r.p.m., then
  r.p.m. remains constant.
• In an airplane with a constant-speed propeller
  these power changes are reflected by manifold
  pressure which is indicated by a meter in the
  cockpit. (The manifold is a part of the exhaust
  passage, its pressure is indicative of the engine
  power.)

20
Carburetor Icing (4)

• Generally you should use full carburetor heat
  whenever you reduce engine r.p.m. below the
  normal operating range, or when you suspect the
  presence of carburetor ice.
• Generally you should not use carburetor heat
  continuously when full power is required, such as
  in take off, due to the decrease in engine output
  with the heated air from the engine
• Be sure to check the POH for recommendation

21
Fuel Injection (1)

• Another type of engine uses Fuel Injection.
• Fuel injection engines remove the carburetor and
  thus avoid carburetor ice problem
• More precise in metering fuel
• More precise in metering fuel-air ratio
• Lower fuel consumption
• Increase horsepower
• Lower operating temperature
• Longer engine life
• Relatively free of induction system icing

22
Fuel Injection (2)

• Fuel injection system has four basic components
• Fuel pump
• Fuel control unit
• Fuel manifold valve (not the exhaust manifold)
• Fuel discharge nozzles
• Fig 2-29

23
Fuel injection systems (2-29)
24
Fuel Injection (3)

• Fuel pump
• pumps fuel from fuel tank to fuel control unit
• Fuel control unit
• replaces carburetor in metering and controlling
  fuel passage based upon mixture control setting
  and throttle setting in the cockpit
• Sends the fuel to the fuel manifold valve
• Fuel manifold valve
• Distribute fuel evenly to the different fuel
  discharge nozzles
• Fuel discharge nozzles
• Introduces air into the fuel
• Inject the mixture into each cylinder head for
  combustion

25
Supercharging and Turbocharging

• Reciprocity engine loses its efficiency at high
  altitude because air density becomes low.
• With the same air volume the actual amount of air
  mixed with the fuel becomes lower.
• This problem can be improved by compressing the
  incoming air.
• Supercharging is a method using a pump to
  compress the air to increase engine efficiency.
• However the pump uses engine power.
• Turbocharging is even more efficient because it
  pressurizes the air using the engine exhaust
  gases (which are disposed anyway).

26
Turbine Engine

• Even with supercharging or turbocharging,
  reciprocity engines can put only about 30 of its
  power into useful work (only one of the four
  strokes are really useful at one time).
• Although not as fuel efficient, the turbine
  engine is much more powerful.
• The four strokes, instead of sequentially
  executed, are carried out simultaneously at
  different sections of the engine (Fig on page
  2-17)
• The power can even be boosted further by using a
  techniques called afterburning inject some raw
  fuel into the exhaust and ignite it again.
• Afterburning is used in some high performance
  planes such as military fighters and supersonic
  planes.

27
Turbine Engine (p. 2-17)
28

• The Ignition System

29
The Ignition System (1)

• The purpose of the ignition system is to provide
  electric sparks in the cylinder heads to ignite
  the fuel-air mixture inside.
• When you turn on the ignition switch electricity
  from the battery of the airplane turns on the
  starter which turns on the crankshaft
• Once the crankshaft is turned it generates an
  independent source of electricity through a
  generator-like system called the magneto. This
  electricity generated by the magneto is totally
  independent of the airplanes electrical system.
• Each cylinder has two spark plugs operated by two
  sets of independent magneto systems. Why?

30
The Ignition System (2)

• This electricity from the magneto causes the
  spark plugs in the cylinder to generate sparks
  that ignites the fuel-air mixture, and thus
  starts the engine moving
• Once the engine moves it continues to move the
  crankshaft, which in turn continue to activates
  the magnetos, which ignite the spark plugs
  through the electricity they generate.
• Turn switch ? moves starter ? moves crankshaft ?
  starts magneto electricity ? produce sparks in
  spark plugs ? ignite fuel ? moves engine pistons
  ? moves crankshaft ? produce magneto electricity
  ? produces sparks in spark plugs .

31
The two independent magneto systems (2-31)
32
Abnormal Combustion (1)

• Because the engine pistons moves very fast and
  the (four) pistons have to move synchronously to
  turn the crankshaft, the timing of the combustion
  in each piston has to be precisely controlled.
• Combustion starts from the spark plugs and
  rapidly but precisely progresses towards the
  cylinder side to completely burn the fuel.
• Two types of abnormal combustion upset this
  precise synchronization detonation and
  preignition.

33
Abnormal Combustion (2)

• Detonation is a sudden explosion of the fuel
  within the cylinder without gradual progression
• It causes excessive temperatures and pressures
  and results in engine roughness, or loss of
  power.
• In severe cases it can lead to damage to the
  piston, cylinder, or valve.
• Detonation happens when the engine is too hot or
  you use a low grade fuel.
• Engine overheat can happen if you takeoff when
  the engine is already hot, or you drive the plane
  above 75 of its power limit for an extended
  period of time, especially using a lean fuel.

34
Abnormal Combustion (3)

• Preignition happens when the fuel is ignited
  before the normal spark.
• Preignition is caused by a residual hot spot in
  the cylinder, caused by any damage around the
  combustion chamber.
• Preignition can also result in engine roughness
  and engine overheat.
• If you suspect detonation or preignition occurs
  you should attempt to lower cylinder temperature
  by slowing the throttle and/or enriching the fuel.

35
Preignition (2-33)
36
Induction

• More information on 4-stroke engines
• http//www.en.wikipedia.org/wiki/Four-stroke_cycle