Induction System, Carburetor, and Mixture

Question 1

It is designed to supply air to the engine so that, when fuel is added, combustion can take place.

Answer 1

induction system

Question 2

Once fuel is added, the fuel/air mixture is delivered into an ________ where it is ducted to the cylinders for combustion.

Answer 2

intake manifold

Question 3

On reciprocating engines, outside air passes through an air intake and is then routed to a ______ or other fuel metering device.

Answer 3

carburetor

Question 4

Reciprocating engine induction systems can be broadly classified as _________, __________, and __________.

Answer 4

normally aspirated, supercharged, turbocharged

Question 5

___________ means that the engine has no supercharger or turbocharger to maintain sea level atmospheric pressure at higher altitudes and, therefore, that it’s maximum available power decreases with ________.

Answer 5

Normally aspirated, altitude

Question 6

A standard induction system on a normally aspirated engine consists of four major components, or sections which are:

Answer 6

• air intake
• induction air filter
• fuel delivery system
• induction manifold

Question 7

An air intake, sometimes referred to as an _______, is designed to direct outside air into a carburetor or other fuel metering device.

Answer 7

air scoop

Question 8

The intake is generally located to take advantage of __________ as much as possible.

Answer 8

ram air pressure

Question 9

For an engine to provide a long service life and a reliable operation, the induction air must be free of any kinds of foreign material. To achieve this property, ______ are typically installed in ________ to prevent sand, dust, abrasive materials, and/or other contaminants from entering the engine.

Answer 9

induction air filters or filters, air intake ducts

Question 10

The fuel delivery system on a normally aspirated engine can be either a _______ or a _________.

Answer 10

carburetor, fuel injection system

Question 11

The purpose of a _________ is to meter the amount of fuel and air that is delivered to the cylinders.

Answer 11

fuel delivery system

Question 12

An ________ typically consists of ducting that goes from the fuel metering device to the individual cylinders.

Answer 12

intake manifold

Question 13

On a typical horizontally opposed engine, the intake manifold is the ________ of all the individual pipes which deliver air or fuel/air mixture to the cylinders.

Answer 13

connecting point

Question 14

One end of each cylinder’s intake pipe is typically bolted to the _______ on each cylinder while the other end is attached to the ______.

Answer 14

cylinder intake port, manifold

Question 15

In some installations, the intake manifold goes through the ______ before it branches out to go to each cylinder which increases the temperature of the fuel/air mixture which, in turn, promotes better ________.

Answer 15

oil sump, fuel vaporization

Question 16

One very important characteristic of an intake manifold is that it must maintain a ________. If a seal is not maintained, air will leak into the intake manifold and lean out the mixture which will cause the engine to run rough.

Answer 16

gastight seal

Question 17

Small induction leaks are most noticeable at idle because the pressure differential between the manifold and atmosphere is greatest at ______.

Answer 17

low rpm

Question 18

Two types of Induction System Arrangements

Answer 18

Updraft Induction System, Downdraft Induction System

Question 19

______ consists of small particles of hard, abrasive material that can be carried by the air and drawn into the engine cylinders; can collect on the fuel metering elements of the carburetor and fuel injector, upsetting the proper relation between airflow and fuel flow at all engine power settings.

Answer 19

dust

Question 20

__________ can be a serious source of trouble to an aircraft engine.

Answer 20

dust and dirt

Question 21

_________ act on the cylinder walls by grinding down these surfaces and the piston rings. Then, they contaminate the oil and are carried through the engine, causing further wear on the bearings and gears.

Answer 21

dirt particles

Question 22

In extreme cases, dirt accumulation may clog an oil passage and cause _______. Likewise, dirt accumulation on fuel injection nozzles affect the fuel/air mixture delivered to the engine.

Answer 22

oil starvation

Question 23

Although dust conditions are most critical at ground level, continued operation under such conditions without ________ results in extreme engine wear and can produce excessive oil consumption.

Answer 23

engine protection

Question 24

When operation in a dusty atmosphere is necessary, the engine may be protected by an alternate induction system air inlet that incorporates a ______.

Answer 24

dust filter

Question 25

This type of air filter system (dust filter) consists of a ________, a _____, and an __________.

Answer 25

filter element, door, electrically operated actuator

Question 26

When the filter system is operating, air is drawn through a ________ that does not face directly into the airstream. With this entrance location, considerable dust is removed as the air is forced to turn and enter the duct.

Answer 26

louvered access panel

Question 27

Since the dust particles are solid, they tend to continue in a straight line. Most of them are separated at this point, those that are drawn into the louvers are easily removed by the _____.

Answer 27

filter

Question 28

In flight, with air filters operating, consideration must be given to possible icing conditions that may occur from actual surface icing or from freezing of the filter element after it becomes _______.

Answer 28

rain soaked

Question 29

Some installations have a ___________ that automatically opens when the filter is excessively restricted.

Answer 29

spring-loaded filter door

Question 30

The installation of __________ prevents the airflow from being cut off when the filter is clogged with ice or dirt. Other systems use an _______ in the filtered air entrance.

Answer 30

spring-loaded filter door, ice guard

Question 31

The ice guard consists of a _________ located a short distance from the filtered-air entrance. In this location, the screen is directly in the path of incoming air so that the air must pass through or around the screen.

Answer 31

coarse-mesh screen

Question 32

When ice forms on the screen, the air, which has lost its heavy moisture particles, passes around the _____ and into the _______.

Answer 32

iced screen, filter element

Question 33

What must the carburetion system do?

Answer 33

• control air/fuel ratio in response to throttle setting and during ac/deceleration
• function at all altitudes and temperatures in the operating range
• provide for ease of starting; may incorporate a means of shutting off the fuel to stop engine

Question 34

The _____________ is the cheapest and simplest arrangement and is used on many light aircraft, however it is very prone to carburetor icing, and may be affected by flight maneuvers.

Answer 34

float-chamber carburetor

Question 35

The _________ is a more sophisticated device and meters fuel more precisely, thus providing a more accurate air/fuel ratio, it is also less affected by flight maneuvers, and is less prone to icing.

Answer 35

fuel injection system

Question 36

Two principles used in simple float chamber carburetor operation

Answer 36

U-tube principle, Venturi principle

Question 37

In terms of the U-tube principle, explain how the liquid would be in a U-tube with equal pressure and differing pressure.

Answer 37

equal pressure = liquid would be of same level on both legs
differing pressure = cause the liquid to flow

Question 38

In practice one leg of the ‘U’ tube is opened out to form a small tank, a constant level being maintained by a _____________ regulating the flow of fuel from a fuel pump (or pumps) delivering a supply from the main aircraft tanks.

Answer 38

float and valve mechanism

Question 39

Bernoulli’s Theorem states that

Answer 39

the total energy per unit mass along any one streamline in a moving fluid is constant

in equation:
P1 + (rho/2)(V1)^2 = P2 + (rho/2)(V2)^2 = C

Question 40

The fluid possesses energy because of its _______, ________, and _______. If one of these changes, one or both of the others must also change to maintain the same overall energy.

Answer 40

pressure, temperature, velocity

Question 41

As the air passes through the restriction of the venturi, its velocity increases, causing a drop in ________ and _________.

Answer 41

pressure, temperature

Question 42

The pressure drop at the throat of the venturi is ________ to the mass airflow, and is used to make fuel flow from the float chamber by placing one leg of the ‘U’ tube in the venturi.

Answer 42

proportional

Question 43

In a float-chamber carburetor, airflow to the engine is controlled by a _______, and fuel flow is controlled by _________.

Answer 43

throttle valve, metering jets

Question 44

________ provides a flow of air from the air intake through a Venturi in the carburetor to the induction manifold.

Answer 44

Engine suction

Question 45

The air speeds up as it passes through the Venturi, and a drop in _________ occurs at this point.

Answer 45

pressure

Question 46

Within the induction manifold however, pressure rises as the throttle is _________.

Answer 46

opened

Question 47

Fuel is contained in a float chamber, which is supplied by ______, or an ___________, or by an _________, and a constant level is maintained in the chamber by a float and needle-valve.

Answer 47

gravity, electrical booster pump, engine-driven fuel pump

Question 48

Where fuel pumps are used, a ________ is included in the system to provide an indication of pump operation.

Answer 48

fuel pressure gauge

Question 49

____________ acts on the fuel in the float chamber, which is connected to a fuel discharge tube located in the throat of the Venturi.

Answer 49

air intake or atmospheric air pressure

Question 50

The difference in pressure between the float chamber and the throat of the Venturi provides the ______ necessary to discharge fuel into the airstream.

Answer 50

force

Question 51

As airflow through the venturi increases, the pressure drop increases, and a higher pressure differential acts on the fuel to increase its ________ in proportion to the airflow.

Answer 51

flow

Question 52

The __________ in the discharge tube determines the quantity of fuel which is discharged at any particular pressure differential, and therefore controls the ________.

Answer 52

size of the main jet, mixture strength

Question 53

Modifications to the Simple Carburetor

Answer 53

pressure balance duct, diffuser well, air bleed diffuser, slow running systems, idle cut-off valve, mixture control

Question 54

In pressure balance duct as modification to carburetor, to maintain the correct rate of discharge of fuel through the main jet, the pressure in the float chamber and the air intake must be _______.

Answer 54

equal

Question 55

Admitting atmospheric pressure in the float chamber by means of a _______ in the float chamber cover plate is not a satisfactory method of ensuring equalized pressure across the carburetor.

Answer 55

drilling

Question 56

Equalized pressure conditions can only be obtained by connecting the float chamber directly to the air intake by a duct which is called the _________.

Answer 56

pressure balance duct

Question 57

As engine speed and airflow through the Venturi increase, the proportion of fuel to air _____ as a result of the different flow characteristics of the two fluids. This causes the mixture to become _______.

Answer 57

rises, richer

Question 58

To overcome the effect which is the mixture becoming richer, some carburetors are fitted with a _________.

Answer 58

diffuser well

Question 59

As engine speed is progressively increased above idling, the fuel level in the diffuser well _____ and progressively uncovers more ________ which allows more air into the discharge tube, and by reducing the pressure differential, prevent enrichment of the air/fuel mixture.

Answer 59

drops, air holes

Question 60

The process of drawing both air and fuel through the discharge tube also has the effect of ____________ more readily, particularly at low engine speeds.

Answer 60

vaporizing the fuel

Question 61

___________ also supplies air to the diffuser and is used in some carburetors to provide altitude mixture control.

Answer 61

Pressure balance duct

Question 62

Pressure balance duct also supplies air to the diffuser and is used in some carburetors to provide __________.

Answer 62

altitude mixture control

Question 63

A ________ applied to a tube immersed in a liquid is sufficient to raise a column of liquid to a certain height up the tube.

Answer 63

suction

Question 64

A suction applied to a tube immersed in a liquid that is sufficient to raise a column of liquid to a certain height up the tube.

Answer 64

air bleed diffuser

Question 65

In an air bleed diffuser, should a small hole be made in the tube, under the same condition, bubbles of air will enter the tube and the liquid will be drawn up the tube in _________ rather than a continuous stream.

Answer 65

smaller drops

Question 66

The liquid will be “diffused” or made to ______ with the air in an air bleed diffuser. The air “bleeds” into the tube and reduces the forces acting on the fuel ________ the flow of liquid through the tube.

Answer 66

intermingle, retarding

Question 67

At low engine speeds, the volume of air passing into the engine is so small that the depression in the choke tube is _________ to draw fuel through the main jet.

Answer 67

insufficient

Question 68

Above the throttle valve, there exists a considerable ________ and this is utilized to effect a second source of fuel supply for slow running conditions.

Answer 68

depression

Question 69

A slow running fuel passage with its own jet leads from the float chamber to an outlet at the lip of the throttle valve. The strong depression at this point gives the necessary _______ to create a fuel flow.

Answer 69

pressure difference

Question 70

The size of the slow-running jet is such that it will provide the rich mixture required for slow-running conditions. An air bleed, opening into the area below the throttle valve, assists ______.

Answer 70

atomization

Question 71

The purpose of the ________ drilled through the throttle valve is to evenly distribute the mixture over the area of the induction manifold.

Answer 71

transverse passage

Question 72

A small hole is drilled into the transverse passage in the __________ side of the throttle valve. It acts as an air bleed to draw some of the fuel through the throttle valve to mix the air passing to the engine.

Answer 72

high pressure

Question 73

As the throttle is opened, the depression at the lip of the throttle valve _______ and the depression in the venturi ______.

Answer 73

decreases, increases

Question 74

As the throttle is opened, the depression at the lip of the throttle valve decreases and the depression in the venturi increases. The main jet starts to ________ and the flow through the slow-running system _______.

Answer 74

deliver fuel, diminishes

Question 75

Carburetors must be carefully tuned in order to obtain a smooth progressive change over between the slow-running and the main system to prevent ‘_________’.

Answer 75

flat spots

Question 76

________ is a period of poor response to throttle opening caused by a temporary weak mixture, it normally makes itself felt as a hesitation during engine acceleration.

Answer 76

flat spot

Question 77

It is usually incorporated in the slow-running passage, and is used when stopping the engine.

Answer 77

idle cut-off valve

Question 78

When the cut-off (idle cut-off valve) is operated, the valve moves over to block the passage to the slow-running delivery, the mixture being delivered to the engine becomes progressively weaker until it will not support _________ and the engine _______.

Answer 78

combustion, stops

Question 79

Operation of the idle cut-off valve prevents any possibility of the engine continuing to run erratically due to _______, and also prevents fuel condensing in the cylinders which would tend to wash the oil from the cylinder walls, causing _________ when the engine is next started.

Answer 79

pre-ignition, lack of lubrication

Question 80

The cut-off may be a separate control or it may be incorporated in the ________.

Answer 80

mixture control lever

Question 81

As altitude increases, the weight of air drawn into the cylinder decreases because the air density ______.

Answer 81

decreases

Question 82

For a given intake velocity, the pressure drop in the Venturi will decrease as ambient density _______.

Answer 82

decreases

Question 83

The fuel flow due to pressure drop will _______ by the same amount and so the mixture will become richer.

Answer 83

not decrease

Question 84

This progressive richness with increased altitude is _______ for economic operation.

Answer 84

unacceptable

Question 85

Types of Mixture Control

Answer 85

needle type mixture control, air bleed mixture control

Question 86

With a __________ mixture control, a cockpit lever is connected to a needle.

Answer 86

needle type

Question 87

In a needle type mixture control, the movement of the cockpit lever inserts or extracts the needle, and varies fuel flow through an orifice to the main jet, thereby controlling the ________.

Answer 87

mixture strength

Question 88

The smallest orifice in the whole fuel system is the _______.

Answer 88

fuel jet

Question 89

To prevent any blockage of the jets by dirt or debris, a ______ can be fitted just before them in the fuel line.

Answer 89

fuel strainer

Question 90

The ________ mixture control operates by controlling the air pressure in the float chamber, thus varying the pressure differential acting on the fuel.

Answer 90

air bleed

Question 91

A small air bleed between the float-chamber and the Venturi tends to reduce air pressure in the float-chamber, and a valve connected to a cockpit lever controls the _________ into the float chamber.

Answer 91

flow of air

Question 92

A small air bleed between the float-chamber and the Venturi tends to reduce air pressure in the float-chamber, and a valve connected to a cockpit lever controls the flow of air into the float chamber. When this valve is fully open the air pressure is greatest, and the mixture is ________.

Answer 92

fully rich

Question 93

A small air bleed between the float-chamber and the Venturi tends to reduce air pressure in the float-chamber, and a valve connected to a cockpit lever controls the flow of air into the float chamber. As this valve is closed, the air pressure decreases, thus reducing the flow of fuel and ________ the mixture.

Answer 93

weakening

Question 94

A small air bleed between the float-chamber and the Venturi tends to reduce air pressure in the float-chamber, and a valve connected to a cockpit lever controls the flow of air into the float chamber. This valve includes a pipe connection to the ________ of the throttle valve. When this pipe is connected to the float-chamber by moving the cockpit control to the ‘_______’ position, float-chamber air pressure is reduced and fuel ceases to flow, thus stopping the engine.

Answer 94

engine side, idle cut-off

Question 95

At power settings above the cruising range, a _________ is required to prevent detonation.

Answer 95

richer mixture

Question 96

The rich mixture required to prevent detonation at power settings above the cruising range may be provided by an ________ or by setting the carburetor to provide a rich mixture for high power and then bleeding off __________ to reduce fuel flow for cruising.

Answer 96

additional fuel supply, float-chamber pressure

Question 97

Some types of carburetor are fitted with an additional needle valve, which may be known as a _________, enrichment jet, or economizer.

Answer 97

power jet

Question 98

The needle valve, which is connected to the throttle control, is fully closed at all throttle settings below that required to give maximum cruising power at sea-level, but as the throttle is opened above this setting the needle valve opens progressively until, at full throttle, it is ________.

Answer 98

fully open

Question 99

A ____________ is used to automatically weaken the mixture for economical cruising.

Answer 99

back-suction economizer

Question 100

When the throttle valve is at a high power setting, the pressure of air flowing past the valve is only slightly below atmospheric pressure, and will have little effect on air pressure in the float chamber, thus a ________ will be provided.

Answer 100

rich mixture

Question 101

As the throttle is closed to the cruising position, air flowing past the throttle valve creates a suction, which is applied to the float-chamber through the _________ and ________.

Answer 101

economizer channel, air jet

Question 102

The reduced float-chamber pressure reduces fuel flow through the main jet to provide the _________ required for cruising.

Answer 102

economical mixture

Question 103

If the throttle valve is opened quickly, airflow responds almost immediately and a larger volume of _____ flows through the carburetor.

Answer 103

air

Question 104

The fuel metering system however, responds less quickly to the changing conditions (throttle valve opening quickly), and a temporary weakening of the mixture will occur, known as a ______ (or at worst causing a ‘______’) before fuel flow again matches airflow.

Answer 104

flat spot, weak cut

Question 105

The fuel metering system responding less quickly to changing conditions is overcome by fitting an _______.

Answer 105

accelerator pump

Question 106

It is linked directly to the throttle; it forces fuel into the Venturi whenever the throttle is opened.

Answer 106

accelerator pump

Question 107

In other pumps, an additional __________ is incorporated to supply an additional quantity of fuel to the engine for a few seconds after throttle movement has ceased.

Answer 107

delayed-action plunger

Question 108

Normally, a _______ would supply fuel to the induction manifold, close to the inlet valve.

Answer 108

priming pump

Question 109

In the absence of a priming pump, it is permissible on some aircraft to prime the engine by __________ (exercising the accelerator pump) several times.

Answer 109

pumping the throttle

Question 110

In the absence of such a device, it is permissible on some aircraft to prime the engine by pumping the throttle (exercising the accelerator pump) several times. This practice must be discouraged in any other circumstances because it increases the chance of __________.

Answer 110

carburetor fires

Question 111

In a simple, light aircraft fuel system, the fuel tanks are rigid tanks fitted in the wings and filled by the ________.

Answer 111

over wing method

Question 112

In a simple, light aircraft fuel system, the fuel is drawn from the tanks by a _________ or _________ fuel pump, through a tank selector, and filter before being delivered to the carburetor.

Answer 112

mechanical, electrical

Question 113

__________ is achieved by use of a priming pump which takes fuel from the filter housing and delivers it to the inlet manifold.

Answer 113

Engine priming

Question 114

The fuel system is monitored for contents and pressure and the fuel drains allow any ______ to be removed before flight.

Answer 114

water

Question 115

Even when an inspection shows that everything is in proper working order and the engine performs perfectly on the ground, ___________ can cause an engine to act erratically and lose power in the air. Many engine troubles commonly attributed to other sources are actually caused by this.

Answer 115

induction system ice

Question 116

It is an operating hazard because it can cut off the flow of the fuel/air charge or vary the fuel/air ratio.

Answer 116

induction system icing

Question 117

_____ can form in the induction system while an aircraft is flying in clouds, fog, rain, sleet, snow, or even clear air that has high moisture content (high humidity).

Answer 117

ice

Question 118

Induction system ice can be prevented or eliminated by raising the temperature of the air that passes through the system, using a _________ located upstream near the induction system inlet and well ahead of the dangerous icing zones.

Answer 118

carburetor heat system

Question 119

Induction System Icing Formations

Answer 119

impact ice, fuel evaporation ice, throttle ice

Question 120

It is caused by visible moisture striking an aircraft and then freezing. Therefore, the air intake and air filter are the areas of an induction system that are most susceptible to this.

Answer 120

impact ice

Question 121

It can also collect at points in an induction system where the airflow changes direction, or where dents and protrusions exist.

Answer 121

impact ice

Question 122

Whenever an induction system encounters this, air flow to the remaining system is restricted. Severe cases of this can cause a total blockage to airflow and complete engine failure.

Answer 122

impact icing

Question 123

sometimes referred to as carburetor ice

Answer 123

fuel evaporation ice

Question 124

It is a result of the temperature drop that occurs when fuel is vaporized.

Answer 124

fuel evaporation ice

Question 125

In a carburetor, as fuel is released into the airstream, it turns into a _______ and absorbs heat from the surrounding air.

Answer 125

vapor

Question 126

In a carburetor, as fuel is released into the airstream, it turns into a vapor and absorbs heat from the surrounding air. This can cause a drop in air temperature of ______. In some cases, this loss of heat is enough to cause the moisture in the air to condense and freeze.

Answer 126

30 deg Fahrenheit or more

Question 127

What part of an aircraft typically accumulates ice before any other part of aircraft in flight?

Answer 127

carburetor

Question 128

Carburetor ice can occur at ambient air temperatures up to ____ and when relative humidity is as low as ____%.

Answer 128

70 deg Fahrenheit, 50

Question 129

Optimum conditions for carburetor ice exist when the outside air temperature is between ___ and ____ and the relative humidity is above _____%.

Answer 129

30 deg Fahrenheit, 40 deg Fahrenheit, 60

Question 130

In a fuel injection system, fuel is injected and vaporized at or near the intake port of each cylinder. In this case, the heat of combustion offsets the temperature drop caused by fuel vaporization. Therefore, __________ is typically not a concern in fuel injected engines.

Answer 130

fuel evaporation icing

Question 131

It is formed on the rear side of the throttle, or butterfly valve when it is in a partially closed position.

Answer 131

throttle ice

Question 132

Why is throttle ice formed on the rear side of the throttle, or butterfly valve when it is in a partially closed position?

It is because as air flows across and around the throttle valve, a _______ is created on the downstream side which has a cooling effect on the fuel/air mixture that causes moisture to accumulate and freeze on the backside of the butterfly valve.

Answer 132

low pressure area

Question 133

basahin mo lang

Answer 133

Since throttle icing typically occurs when the butterfly valve is partially closed, a small amount of ice can cause a relatively large reduction in airflow and a corresponding loss of engine power.

Question 134

In severe cases, a large accumulation of ice can jam the throttle and render it __________.

Answer 134

immovable

Question 135

Since the temperature drop created by the low pressure area is not that great, throttle ice seldom occurs at temperatures above ___°F.

Answer 135

38

Question 136

____________ causes heated air, from the region of the exhaust pipe, to be fed into the induction system. The heated air will then melt ice. The ice then passes through the engine as _________.

Answer 136

Carburetor heat system, water

Question 137

The carburetor heat is operated by a _______ in the cockpit.

Answer 137

push-pull control

Question 138

A ____________ is located below the carburetor for selecting an alternate warm air source (carburetor heat) to prevent carburetor icing.

Answer 138

carburetor heat air valve

Question 139

During normal operation, the carburetor heat valve admits air from the __________.

Answer 139

outside air scoop

Question 140

During icing conditions, the carburetor heat valve admits warm air from the ___________.

Answer 140

engine compartment (cowling)

Question 141

The pilot normally performs a pre-takeoff check of the __________ before each flight. Technicians frequently test the system as part of their engine evaluation during inspections or when performing engine troubleshooting measures.

Answer 141

carburetor heat system

Question 142

A normal response during the application of carburetor heat is a ____________. Should the engine lose more than the normal amount of rpm, a system fault is present.

Answer 142

slight reduction of rpm

Question 143

rich mixture ratio

Answer 143

8:1

Question 144

weak mixture ratio

Answer 144

30:1

Question 145

chemically correct mixture ratio

Answer 145

14.7:1 or 15:1

Question 146

At this ratio, all of the oxygen in the air combines with all of the hydrogen and carbon in the fuel.

Answer 146

14.7:1 or 15:1

Question 147

The _________ does not give the best results because the temperature of combustion is so high that power can be lost through detonation.

Answer 147

chemically correct mixture

Question 148

The chemically correct mixture does not give the best results because the temperature of combustion is so high that power can be lost through _________.

Answer 148

detonation

Question 149

Although the chemically correct mixture strength would theoretically produce the highest temperature and therefore power, in practice, _____________ are less than perfect. This results in some regions being richer and others being weaker than the optimum strength. This variation may exist between one cylinder and another.

Answer 149

mixing and distribution

Question 150

A slightly rich mixture does not have much effect on power since all the oxygen is still consumed and the excess of fuel serves to slightly reduce the effective __________.

Answer 150

volumetric efficiency

Question 151

The cooling effect of the evaporating fuel can be to some extent beneficial preventing ________.

Answer 151

detonation

Question 152

______ mixtures rapidly reduce power since some of the inspired oxygen is not being utilized, and this power reduction is much greater than that resulting from slight richness.

Answer 152

weak

Question 153

It is quite common to run engines (when maximum power rather than best fuel economy is the objective) at somewhat ________ than chemically correct mixtures to ensure that no cylinder is left running at severely reduced power from being unduly weak.

Answer 153

richer

Question 154

A mixture which is weaker than the chemically correct ratio, besides burning at a lower temperatures, also burns at a _________ (because of the greater proportion of nitrogen in the cylinder).

Answer 154

slower rate

Question 155

Power output decreases as the mixture is weakened, but, because of the increase in efficiency resulting from cooler burning, the fall in power is proportionally less than the decrease in fuel consumption. Thus, the specific fuel consumption (S.F.C.), decreases as the mixture strength is weakened below _____.

Answer 155

15:1

Question 156

For economical cruising at moderate power, air/fuel ratios of _____ may be used, an advance in the ignition timing being necessary to allow for the slower rate of combustion.

Answer 156

18:1

Question 157

With extremely weak mixtures, the gases may still be burning when the exhaust valve opens, exposing the valve to high temperatures which may cause the valve to _________.

Answer 157

crack or distort

Question 158

With extremely weak mixtures, the gases may still be burning when the exhaust valve opens. As the inlet valve opens, the heat of the exhaust gases is still so high that it may ignite the mixture in the induction system, and ‘_______’ occurs through the induction manifold.

Answer 158

popping back

Question 159

The slow burning caused by weak mixtures also causes _______, as a certain amount of heat is not converted into work by expansion and has to be dissipated by the cooling system.

Answer 159

overheating