Mechanics > Ignition > Flashcards

Ignition Flashcards

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1
Q

What is the purpose of ignition?

A

To allow combustion of air-fuel mixture

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2
Q

What is the ignition system divied into?

A

Primary and secondary circuit

That are electrically separated

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3
Q

What do the primary and secondary circuit do?

A

Primary circuit connects to car’s main 12V electrical system

Secondary circuit delivers high voltage to the spark plugs

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4
Q

What is the ignition coil comprised of?

A

Primary and secondary windings around a soft IRON core

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5
Q

How does the ignition coil act as a transformer?

A

Control system causes the primary winding to gradually build a magnetic field

When a spark is required, the magnetic field collapses suddenly, inducing a voltage in the secondary winding

Backward EMF occurs causing the increase in voltage through the secondary winding (many more turns in secondary windings)

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6
Q

How have ingition systems evolved over time?

A

Used to use mechanical distributor for both timing control and spark distribution

Now fully electronic spark timing and distribution systems have become standard
(coil pack for distrbution and ECU for timing control)

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7
Q

What is the ignition called that uses a mechanical distributor?

A

Breaker point ignition

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8
Q

How does a mechanical distributor work?

A

Inside the distributor is a cam that operates a spring-loaded switch known as the points

When the points closed it energizes the primary coil

The magnetic field collapses when the points are open

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9
Q

What can occur when the points are open? And what helps reduce this?

A

Spark arcing between the contacts

Condenser/Capacitor helps the magnetic field collapse more quickly to reduce arcing

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10
Q

What is the role of hte condenser/capacitor?

A

Helps the magnetic field collapse more quickly to reduce arcing

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11
Q

Why is arcing of the spark bad?

A

Arcing erode sthe point

So the ignition timing becomes inaccurate

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12
Q

Name some maintenance break point ignition requires

A

Need to adjust the points gap

Replace components more frequently

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13
Q

What is points bounce?

A

When the camshaft is turning so fast it bounces away

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14
Q

What is found in the distrbutor cap to distrbute the spark?

A

Carbon brush

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15
Q

Where is the king lead found and what is its role?

A

It is the center contact in the distrbutor

High voltage is fed down it to the engine-driven rotor

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16
Q

How does distributorless ignition work? (direct ignition)

A

Plugs are connected directly to the coil

(reduces loss of spark jumping)

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17
Q

What does a double-ended coil allow in the distributorless ignition?

A

Connects two spark plugs for a pair of cylinders on opposite strokes

BOTH plugs spark the the same time on thee very engine revolution

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18
Q

What materials are the spark plug wires made of?

A

Carbon-stranded conductor

Silicone insulator

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19
Q

What materials is the spark plug made of?

A

Central COPPER electrode

Aluminium oxide ceramic insulator

STEEL shell electroplated with NICKEL

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20
Q

What does it mean for the spark plug to be electrically grounded?*

A
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21
Q

What are the typical components of a spark plug?

A

Terminal

Ribbed insulator

Shell

Conductive seal

Centre electrode

Insulator nose

Ground electrode

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22
Q

Why is the insulator ribbed?

A

Increases surface are to reduce flashover to the ground

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23
Q

Where is the gound electrode welded to?

A

The shell

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24
Q

What are the thread diameters of spark plugs?

A

10,12,14,18mm thread diameters

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25
What happens if the spark gap is too small or large?
If it is too small = weak spark is produced If it is too large = mixture will burn inefficiently
26
What is the spark plug reach?
How long the threaded portion is (indicates how far into cylinder head it will go)
27
What are the different types of spark plug seating?
Flat seating Spark plugs must be fitted with a metal washer to seal combustion chamber and remove heat Conical / Taper Seating No washer required as plug is sealed by its conical seat (cone face)
28
What ist he ideal spark plug tip temperature?
500-850 degrees Celsius
29
What happens if the spark plug tip temperature is too high or too low?
If temp is too low = carbon and combustion chamber deposits will not be burnt off (Carbon and oil fouling will occur) If temp is too high = the plug may overhead, damaging the electrodes (Start burning the electrode off Pre-ignition can also occur)
30
What can spark plugs remove?
Combustion chamber HEAT
31
How is combustion heat dissipated and by what %?
2% is absorbed by spark plug wires 20% is absorbed by the insulator and spark plug side walls 58% is absorbed by the cylinder head walls 20% is absorbed by intake stroke fresh air
32
What determines how much heat spark plugs can remove?
Insulator nose length Gas volume around the insulator nose Composition of the insulator and the center electrode
33
What is the difference between a hot and cold spark plug?
Hot plug Long insulator nose = exposing a large surface area to combustion gases Dissipates heat slowly = so it remains hot Firing end heats up quickly Cold plug Shorter insulator nose = minimizing surface area exposed to combustion gases Dissipates heat quickly Firing end heats up slower
34
What is the advantage of spark plugs with multiple ground electrodes?
They produce multiple spark paths = reduces spark erosion
35
What are resistor spark plugs and there advantages?
Spark plug with carbon compound resistor in center core The resistor suppresses radio frequency interference (RFI)
36
What is a surface discharge plug and its advantages?
Creates a spark that jumps along the insulator surface (like a flat face) from the center electrode to the shell (rather than across a gap between two protruding electrodes) Better fouling resistance, consistent gap, and improved flame kernel growth in high-performance or demanding engines, although they can be pricier and less common for standard cars
37
What are the steps to spark plug removal?
Remove the lead from each plug, by using a rubber boot Slacken each spark plug Use an airline/brush to remove all debris from around each plug Remove all plugs and place on bench in cylinder order (helps with diagnosing) Inspect each spark plug
38
What causes white smoke?
Burning coolant
39
What causes blue smoke?
Burning oil
40
What causes black smoke?
Burning fuel
41
What causes bubbling?*
42
What are the steps to spark plug gap adjustment?
Obtain gap information from Auto data Check gap between electrodes with a feeler gauge It should be a sliding fit If necessary, adjust gap suing feeler gauge tool (if too big an just tap it on the bench)
43
What are the steps to fitting spark plugs?
Apply grease to spark plug threads (check to see if it is put in dry) ---Lubrication can mean it screws in tighter and can crack the cylinder head (esp tapered) Hand screw spark plugs into cylinder head Tighten plugs as per Auto data Refit the spark plug leads
44
Why were ignition systems improved?
To minimize ehause emssion
45
What are the typical components of the electonic ignition system?
Ignition module Ignition coils Crankshaft sensor Trigger wheel (attached to crankshaft)
46
What are the advantages to the electronic ignition system?
Fewer moving parts No mechanical timing Less mainentance No mechanical load on engine (not actually much effort to turn distributor using the camshaft) Increased coil saturation
47
The electronic system secondary circuit produces two sparks, what is the THEORETICAL output voltage of the 'waste' spark? And what is it in practice?
Should be equal in magnitude, but opposite in polarity But in practive, the 'waste' spark voltage is smaller Event spark 20,000 V Waste spark 1000V
48
What are the advantages of direct ignition systems?
No spark plug leads, therefore no RFI No coil packs to worry about, reduced number of components = cheaper No mechanical wear due to moving parts Compact packaging Nowhere to lose spark energy to
49
What does CDI system stand for?
Capacitor Discharge Ignition System
50
How does a CDI system work?
Widely used in racing for high RPM operation Uses a capacitor to store energy that is discharged through a coil, at the required firing time Power supply converts 12V DC into 400V, to charge the capacitor Diode = directs current one way When a spark is required, the capacitor is discharged through a primary winding This produces a high voltage pulse across a secondary winding (typically 50,000V) Charging and discharging timing is controlled by the computer (ECU)
51
What is the discharge time of a CDI system?
Discharge time 150-500microseconds
52
What problem do modern CDI systems overcome and how?
Modern CDI systems produce multiple sparks to overcome poor combustion problems with lean mixtures
53
How is the combustion process optimized in the fuel injection phase?
injection is divided into two phases At pre-injection, a small amount of fuel is injected before thee piston reaches TDC The resultant rise in temperature and pressure shortens the main ignition delay and reduces pressure fluctuations The benefits include lower combustion noise and reduced exhaust emissions
54
How is the fuel injector held closed?
When the solenoid is de-energized, the outlet restrictor is held closed by spring pressure The balance of hydraulic forces acting on the nozzle needle keep it pressed against a seat This seals the higher pressure chamber and no fuel can enter the combustion chamber
55
How does fuel injection begin?
When current is applied to the solenoid valve, it opens very rapidly The spring pressure is overcome and the outlet restrictor now opens, allowing fuel to flow out of the control chamber The forces acting on the nozzle plunger reduce and allow it to move upwards This opens the nozzle jets and high pressure fuel injection starts
56
What happens to the forces during fuel injection?
An equilibrium is reached when the needle plunger reaches an upper stop The injection pressure is nearly equal to the rail pressure and the nozzle jets are fully open The quantity of fuel injected is proportional to the length of time that the solenoid is open
57
How does fuel injection end?
When current is removed from the solenoid, it is de-energized and closes The armature is pressed down by the spring force and the outlet restrictor closes The pressure in the control chamber rises, causing the nozzle plunger to move downwards and back to its closed position The nozzle jets closes and fuel injection cycle is complete
58
How do piezo crystals work in the knock sensor?
Crystal distorts with knocking noise = as it vibrates it generates electricity More knock = more electricity produced; ECU gets this signal and adjusts accordingly Probably retards fuel ignition = driver will notice that engine performance decreases, but knocking sound stops
59
How is fuel delivered from back to front of car?
Fuel tank (Fuel level sensor) Fuel Pump Fuel hose/pipe (Pressure sensor) Fuel injectors
60
What is an open loop and what is a closed loop?
Open loop = ECU uses preprogrammed values to control engine (used when car starts up and there are no sensor inputs) Close loop = injection profile adjusted by ECU based on sensor inputs
61
What does ROM stand for?
Read only memory
62
Where is injector found in single point EFI system?
Injector located inside throttle body, sits on top of inlet manifold Injector sprays fuel from above throttle valve ECU controls injector opening
63
Where is injector found in multipoint EFI system?
Injector based in each branch of inlet manifold below throttle valve Injectors spray fuel directly into each port ECU controls opening of injectors
64
What are the different types of fuel injection timing?
Intermittent (or modulated) ----Injectors controlled independently of inlet valve position Timed (or sequential) ----Injectors controlled in time with inlet valves Continuous ----Injectors open all the time, fuel pressure is controlled
65
What are the different types of fuel injector opening relationships?
Simultaneous injection = all injectors firing together (Wasteful because will be spraying onto the back of a valve) Sequential injection = one injector firing at a time Group injection = injectors of Vee engine operating in A and B banks
66
What other component operates in open and closed loops too?
Catalytic converter
67
What are the typical fuel systems and subsystems?
Fuel Supply System >>>Supplies clean fuel to fuel metering system (fuel pump, filter, pipes) Air Supply System >>>Supplies controlled clean air to engine (air filter, ducting) >>>Turbos factor into this too Fuel Metering System >>>Controls amount of fuel (and air) entering engine (injectors, pressure regulator, throttle valve)
68
What are the advantages of common rail disel injection?
Improved performance Lowered fuel consumption Quieter engines
69
What are the components of common rail disel injection?
Low pressure pump Low pressure filter Overflow valve Return manifold High pressure pump Pressure Control Valve Rail pressure sensor Rail Fuel injectors ECU (aka EDC = electronic diesel control) Fuel Temperature Sensor Other sensors
70
What is the role of the low pressure pumps?
Supplies fuel to the high pressure pump
71
What is the role of the fuel filter?
It is vital that this is replaced in line with manufacturers recommendations to ensure system cleanliness and lifespan
72
What is the role of the overflow valve?
Enables excess fuel to overflow back into the fuel tank
73
What is the role of the return manifold?
Controls the return of fuel back to the fuel tank
74
What is the role of the high pressure pump?
Heart of fuel system = where diesel fuel has its pressure increased It is engine driven, system dependent and can generate excess of 2000 bar
75
What is the role of the high pressure control valve?
Controls pressure generated within the pump electronically (ECM controlled)
76
What is the role of the rail pressure sensor?
Monitors system pressure
77
What is the role of the common rail
Where fuel is stored and passed into the injectors for injection
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