Carburation

Question 1

Gasoline will not burn unless it is first vaporised and then mixed with ______ which is normally obtained from the ______.

Answer 1

oxygen; air

Question 2

The workable limits of fuel-air ratio for reliable ignition by spark are from as rich as 1:______ to as lean as 1:______.

Answer 2

1:9; 1:18

Question 3

The ‘chemically correct’ or stoichiometric mixture is very close to 1:______. In theory, at this mixture strength, complete combustion of both the ______ and ______ will occur. In a richer mixture some ______ will be left over after combustion. In a leaner mixture, some ______ will be left over.

Answer 3

1:15; fuel; oxygen; fuel; oxygen

Question 4

In practice, it has been found that maximum power output is achieved with a relatively rich mixture strength of about 1:______, and best economy with a relatively weak mixture around 1:______.

Answer 4

1:12; 1:16

Question 5

Aircraft carburettors are typically set up to operate with a rich mixture at (idling / cruise / high) power settings, and with a lean mixture at (idling / cruise / high) power.

Answer 5

rich for idling and high power; lean for cruise

Question 6

In normal operation, fuel will flow from the float chamber through the main jet of the carburettor because the air pressure above the fuel in the float chamber is (at ambient / higher than ambient) pressure while the venturi air pressure affecting the jet is at (ambient / lower than ambient) pressure.

Answer 6

pistions fit closely within the cylinders. Three or more grooves are machined around the piston near the top into which are set the steel pistion rings. The function of the upper rings is to prevent combustion gases from escaping between the pistion and cylinder walls. The lower piston ring is usually desinged to prevent lubricating oil from entering and being burnt in the combustion space. The piston is what compresses the fuel air mixure.

Question 7

Atomisation and diffusion of the fuel leaving the main jet (improves / prevents) vaporisation and even mixing with the air.

Answer 7

improves

Question 8

The density (and inertia) of the fuel is (higher / lower) than that of the air. Hence, an accelerating system is required to provide extra (fuel / air) to maintain the mixture strength when the throttle is opened.

Answer 8

higher; fuel

Question 9

A separate idling system is required because, at low rpm:

A. The main jet provides too much fuel.

B. With little difference in air pressure between the float chamber and venturi, the flow of fuel from the main jet drops to zero or becomes unreliable.

Answer 9

B. With little difference in air pressure between the float chamber and venturi, the flow of fuel from the main jet drops to zero or becomes unreliable.

Question 10

Idling fuel is drawn from an outlet (a jet) situated (near the gap between the butterfly valve and carburettor wall / in the middle of the venturi).

Answer 10

near the gap between the butterfly valve and carburettor wall

Question 11

The phasing out of the idling system and phasing in of the main fuel metering system takes place typically between ______ rpm and ______ rpm.

Answer 11

1000; 1400

Question 12

A power enrichment system is needed at high rpm and manifold pressure to avoid ______ and ______.

Answer 12

overheating; detonation

Question 13

A mixture control system is needed because, as an aircraft climbs, the carburettor will meter (less / the same weight of) fuel into a decreasing weight of air, making the mixture (too rich / too lean).

Answer 13

the same weight of; too rich

Question 14

The idle cut-off part of the mixture control system operates by ______ the fuel supply at the carburettor.

Answer 14

cutting off

Question 15

The two main disadvantages of the float-type carburettor are that fuel flow can be interrupted by manoeuvres and ______ and susceptibility to ______.

Answer 15

turbulance; icing

Question 16

The pressure injection carburettor (has / does not have) a float chamber. A ______ is still used to measure the amount of air entering the engine and a fuel pressure regulator unit varies the amount of ______ in the mixture.

Answer 16

does not have; venturi; fuel

Question 17

The main jet (or discharge nozzle) of the pressure-injection carburettor is (ahead of / on the engine side of) the throttle butterfly. This makes it (less / more) susceptible to carburettor icing than the float-type carburettor.

Answer 17

on the engine side of; less

Question 18

Other advantages are that it (will / will not) operate when inverted, has (more / less) accurate fuel metering, has better ______ and mixing and there is (less / a greater) chance of vapour lock.

Answer 18

will; more; atomisation; less

Question 19

Fuel injection systems (have / do not have) a carburettor. The fuel is injected into the intake air as a high-pressure spray near the inlet valve or ______ impeller or, on some large engines, directly into the ______ chamber. The amount of air (and therefore of the mixture) is controlled in the normal way through ______ butterfly valve.

Answer 19

do not have; supercharger; combustion; throttle

Question 20

In a continuous flow system, the fuel is injected ______ into the intake manifold air at the inlet port of each cylinder. In a direct injection system, the fuel is injected directly into the cylinder, only during the ______ stroke.

Answer 20

continuously; induction

Question 21

Which of the following are true?

The advantages of fuel injection systems are:

A. Freedom from refrigeration ice.

B. More accurate delivery of the mixture to Individual cylinders.

C. Improved control of the mixture and therefore increased engine efficiency.

D. Better throttle response.

E. Less susceptibility to vapour lock and fuel contamination.

Answer 21

A, B, C and D are true.

E is not true - fuel injection systems are more susceptible.

Question 22

The mixture control is almost always placed in ______ ______ for takeoff.

Answer 22

full rich

Question 23

As the aircraft is climbed with the mixture in FULL RICH, the excess fuel in the mixture assists in ______ the engine and helps to prevent ______.

Answer 23

cooling; detonation

Question 24

To lean the mixture manually for the cruise, you should move the mixture control toward the lean position until the rpm begin to ______ and the engine shows signs of running a little ______. Then move the control back toward rich to regain best ______ and the engine runs ______. Finally, move the mixture control to a slightly ______ position.

Answer 24

drop; roughly; rpm; smootly; richer

Question 25

The mixture control is normally placed in ______ ______ at top of descent.

Answer 25

full rich

Question 26

If leaning the mixture using an EGT gauge, this will involve moving the mixture control toward lean until a in EGT is observed and then moving the control to the ______ ______ side until a specified drop in EGT is obtained.

Answer 26

peak; rich

Question 27

Which of the following is true? An over-rich mixture can cause:

A. Rough running

B. A loss of power

C. Fouling of spark plugs

D. Possibly lead deposits on piston and valves

E. Excessive cylinder head temperatures

Answer 27

A, B, C and D are true.

E is not true - a rich mixture results in cooling.

Question 28

An over-lean mixture can cause excessively (low / high) cylinder head temperatures, possibly leading to ______.

Answer 28

high; detonation

Question 29

State the three forms of carburettor ice.

Answer 29

refrigeration; throttle; impact

Question 30

Refrigeration ice is caused by the ______ of fuel.

Answer 30

­ vaporisation

Question 31

Throttle ice arises because of the drop in ______ though the venturi and especially past the ______ throttle.

Answer 31

pressure; butterfly

Question 32

Refrigeration and throttle ice (can / cannot) form if ambient air temperatures are well above freezing (up to +25 °C) when the relative humidity is above 50%.

Answer 32

can

Question 33

Refrigeration and throttle ice are most likely to form when the temperature of the fuel-air mixture inside the carburettor has dropped into the range 0°C to ______°C. Visible moisture (is / is not) necessary for its formation.

Answer 33

-10°C; is not

Question 34

Impact ice is likely to occur (and affect the carburettor) when the ambient air temperature is near or below ______°C and when ______ moisture is present.

Answer 34

0°C; visible

Question 35

Symptoms of carburettor ice formation are: a loss of engine ______ and ______ running.

Answer 35

power; rough

Question 36

The remedy for carburettor ice is to apply ______ ______.

Answer 36

carburettor heat

Question 37

If carburettor ice is suspected, apply ______ carburettor heat. Initially, it may be expected that the engine will run very (roughly / smoothly), but this should disappear once the ice is ______.

Answer 37

full; roughly; melted

Question 38

Once the ice has been cleared from the carburettor, the carburettor heat should be (left in full hot / left partially on / removed).

Answer 38

removed

Question 39

In extreme conditions, when carburettor ice continues to form, you have only two options.

Which is the preferred option?

A. To operate the engine with full carburettor heat continuously applied, or

B. To fly out of the extreme icing conditions if this can be done safely.

Answer 39

B. To fly out of the extreme icing conditions if this can be done safely.

Question 40

The likelihood of carburettor ice forming is (increased / decreased) in a descent when the throttle butterfly is nearly closed. Therefore, for descent, especially on a cool/high-humidity day, would it be advisable to set the carburettor heat to full hot? If so, at what point should carburettor heat be removed.

Answer 40

increased; yes; on short final approach to land

Question 41

The continuous use of carburettor heat on the ground should be avoided because in most aircraft the source of hot air is (filtered / unfiltered).

Answer 41

unfiltered