Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

ice > exam 2 > Flashcards

exam 2 Flashcards

1
Q

What components are included in an engine intake system?

A

Intake manifold, throttle, intake valves, and carburetor or fuel injectors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does the intake manifold do?

A

Delivers air and fuel to each cylinder via runners.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

List the types of fuel addition in an intake system.

A

Carburetor (upstream), Throttle body injection (upstream, common to all cylinders), Multi-port injection (downstream, before valves, dedicated to each cylinder), Direct injection (into cylinder)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What design features improve intake runner performance?

A

Proper sizing for balance between pressure drop and turbulence, smooth bends, no protrusions, sometimes variable size based on engine speed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the advantages of direct fuel injection?

A

Higher volumetric efficiency, consistent air-fuel (AF) ratio, no need for heated manifold, larger diameter runners possible.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the forms of fuel flow in the intake manifold?

A

Vapor in air, Liquid droplets in air, Liquid on runner walls

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What issues can liquid fuel on intake walls cause?

A

AF sensitivity to geometry, hard to adjust AF with rapid airflow changes, inconsistent AF mixture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is volumetric efficiency in SI engines and why is it important?

A

Ratio of actual air intake to theoretical max; affects engine performance and varies with speed and design.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How does early fuel addition affect volumetric efficiency?

A

Lowers efficiency as vapor displaces air.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How does valve overlap affect volumetric efficiency?

A

Exhaust gases can displace fresh charge, reducing efficiency—especially at lower speeds.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What factors cause friction losses in intake systems?

A

Flow resistance through components, turbulent losses increase with speed, poor runner design (sharp bends, gaskets)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is choked flow?

A

When airflow reaches sonic velocity and is no longer influenced by downstream pressure—often at valves or carburetors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why does intake valve timing matter?

A

Optimizing closing time after BDC maximizes volumetric efficiency. Timing is fixed in older designs but variable in modern systems.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is intake tuning and how does it work?

A

Uses pressure wave reflections in intake runners to boost air into cylinder at certain speeds—optimized for a design RPM.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is Exhaust Gas Recirculation (EGR)?

A

Recycling up to 20% exhaust back into the cylinder to reduce combustion temp, emissions, and volumetric efficiency.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are intake valves typically made of, and how do they operate?

A

Hardened steel poppet valves; spring-closed and camshaft-opened.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is valve lift (lmax) and how is it related to flow area?

A

Max distance a valve opens; Apass = π × dv × l (dv = valve diameter)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Define valve discharge coefficient (CDv).

A

CDv = Aact / Apass; accounts for flow separation and smaller effective area.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How does variable valve control (VVC) enhance performance?

A

Adjusts valve timing, duration, and overlap to optimize performance across RPM range—improves power, torque, emissions, and fuel economy.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the benefits of electromechanical valves?

A

No camshaft, less friction, flexible timing, supports higher temps, improves performance.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are fuel injectors and how do they operate?

A

Nozzles spraying fuel into air; electronically controlled based on feedback (e.g., oxygen sensor, engine speed, throttle position).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the types of fuel injection systems?

A

Throttle body injection, Multipoint port injection, Direct injection (GDI)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are the advantages of gasoline direct injection (GDI)?

A

Stratified mixtures, lean burn under light loads, better fuel economy, reduced knock and emissions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What are the three stratified mixture modes in GDI?

A

Light load: Lean 50:1, Medium load: Richer 20:1, High load: All early injection for max power

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What is a carburetor and how does it work?
Fuel delivery device that uses a venturi to draw fuel via pressure drop; controls AF ratio using throttle, choke, and various valves.
26
What are the key components of a carburetor?
Venturi, Throttle, Capillary tube, Float valve and reservoir, Idle valve and adjustment, Choke, Acceleration pump
27
What are common carburetor issues and design considerations?
Rich/lean mix based on throttle position, cold start issues, AF distribution imbalance, icing, complexity vs. injection systems
28
What is supercharging?
Mechanically driven intake compressor boosting air pressure; provides more power, but adds load, noise, and weight.
29
What is turbocharging and how does it differ from supercharging?
Uses exhaust-driven turbine to compress intake air; more efficient but can suffer turbo lag.
30
What are common super/turbocharger controls?
Air bypass, Variable blade pitch, Aftercoolers to reduce air temp and knock risk
31
What are dual-fuel engines and give an example.
Engines that use two fuels (e.g., diesel and natural gas); diesel helps ignite cheaper natural gas.
32
What’s unique about two-stroke engine intake?
Requires pressurized intake, no exhaust stroke, simpler design but emissions challenges.
33
What are the types of two-stroke scavenging?
Cross, Loop, Uniflow/Throughflow
34
How is fuel injected in two-stroke engines to reduce emissions?
After exhaust valves close, direct injection avoids fuel loss during scavenging.
35
What makes CI engine intake different?
No throttle, fuel added late, turbocharging common, high pressure fuel injection (20-200 MPa)
36
How does nitrous oxide boost engine power?
Adds oxygen to allow more fuel to burn; evaporative cooling increases intake density—can double or triple power output.
37
What are the primary motions of air, fuel, and exhaust in the cylinder?
Turbulence, Swirl, Squish, Tumble, Crevice flow, Blowby.
38
What does turbulence do in the combustion chamber?
Increases heat transfer, fuel evaporation, air-fuel mixing, and combustion rates.
39
What is swirl and how is it quantified?
Bulk rotational motion in the cylinder, quantified by Swirl Ratio (typically 5–10).
40
When is swirl highest and lowest during the engine cycle?
High during intake and combustion; low during compression and expansion.
41
What is squish?
Inward flow as piston approaches TDC, promoting air-fuel mixing.
42
What is tumble?
Secondary rotational motion caused by piston face contours, helps stratify mixture.
43
What is tumble ratio?
Tumble angular speed / engine speed, typically 1 to 2.
44
What are divided combustion chambers?
Separate into main (80%) and secondary (20%) chambers for better combustion.
45
How does the SI engine use divided chambers?
Secondary chamber with rich mix and spark generates torch to ignite lean mix in main chamber.
46
How does the CI engine use divided chambers?
Passive secondary cavity evens piston pressure.
47
What is crevice flow?
Air-fuel trapped in small volumes (1-3%) that may not combust.
48
Why is crevice flow a problem in SI engines?
Up to 20% of air-fuel mixture trapped and unburned; less issue in CI due to late injection.
49
What is blowby?
Gases passing piston rings into crankcase.
50
How is blowby controlled?
Compression rings and precise machining; crankcase vented to intake manifold.
51
What are the benefits of mathematical modeling?
Reduces testing costs, enables simulation of combustion dynamics.
52
Why are computer simulations used?
Engine control and design testing using sensors and assumptions; useful but not infallible.
53
What are the three regions of SI combustion?
Ignition and flame development, Flame propagation, Flame termination.
54
When does spark occur in SI engines?
10 to 30 degrees before TDC.
55
What affects spark plug performance?
Voltage (25k–40kV), current (200A), temp (650–950°C), gap size (0.7–1.7mm).
56
What promotes spherical flame growth?
Richer mixture near spark, plug near intake valve.
57
What is the burn angle?
Crank angle during flame propagation, typically about 25 degrees.
58
Why advance spark at high speed?
Less time for combustion.
59
Why advance spark at idle?
Slow flame propagation.
60
What causes flame termination?
Fuel near walls/corners, more heat loss, low turbulence.
61
What causes cylinder-to-cylinder combustion variation?
Runner length/temperature, injector differences.
62
What causes cycle-to-cycle combustion variation?
Low speed/load, fuel mixture fluctuations.
63
What controls combustion in modern engines?
Sensors (throttle, temp, O2, knock, etc.) and actuators (timing, injection, etc.).
64
What is stratified charge combustion?
Rich mix in secondary chamber ignites leaner main chamber.
65
What is the typical lean mix ratio in stratified charge?
Around 25:1.
66
What are power operation traits?
Rich mixture, retarded timing, high emissions.
67
What are cruise operation traits?
Lean mix, high EGR, efficient, low emissions.
68
What happens during idle or low speed?
High exhaust residual, rich mix, misfires.
69
What happens when throttle closes at high speed?
Vacuum, rich mix, poor combustion, high emissions.
70
Why is starting a cold engine difficult?
Poor vaporization, cold surfaces, low speed.
71
What are fast-burn combustion chamber features?
High turbulence, short burn distance, small chamber, edge plug location.
72
What are CI combustion characteristics?
Unsteady, non-homogeneous, swirl/turbulence needed, high efficiency.
73
When is CI fuel injected?
From 15° before to 5° after TDC.
74
What are the stages of CI combustion?
Atomization, Vaporization, Mixing, Self-ignition, Combustion.
75
What affects CI ignition delay?
Temperature, pressure, engine speed, compression ratio.
76
What is cetane number?
Measure of ignition delay (low CN = long delay).
77
What causes soot in CI engines?
Rich zones, poor mixing; avoid with leaner mixes.
78
How do high compression engines help?
Can burn any fuel, more efficient, used in military.
79
What cold weather problems do CI engines face?
Cold walls, hard starts, require glow plugs, fuel heating.
80
What is HCCI?
Homogeneous Charge Compression Ignition—experimental, uses dual fuels, late diesel injection.
81
What is variable compression ratio tech?
Adapts compression for load/fuel via moving parts (hinges, rods).
82
What are the two stages of exhaust?
Blowdown and exhaust stroke.
83
When does blowdown begin?
40 to 60 degrees before BDC.
84
What are typical blowdown conditions?
4-5 atm pressure, 1000K temp, exhaust pressure ~1 atm.
85
Why is exhaust valve timing important?
Too early wastes power; too late causes pumping losses.
86
What is choked flow during blowdown?
When pressure ratio is high enough for sonic velocity at the valve.
87
Where does turbocharger benefit from blowdown?
Kinetic energy from high-speed exhaust gases.
88
When does exhaust valve close?
8 to 50 degrees after TDC.
89
Why do intake and exhaust valves overlap?
Helps scavenging but can increase residuals.
90
Why are exhaust valves smaller than intake valves?
Higher temp and pressure differences enable faster flow.
91
What are typical SI engine exhaust temps?
400–600°C (design), 300–400°C (idle), 900°C (max speed).
92
What are typical CI engine exhaust temps?
200–500°C, lower due to leaner mix and more expansion cooling.
93
Why is the exhaust manifold thermally coupled to intake?
Helps vaporize incoming fuel.
94
What does a thermal converter do?
Burns CO in manifold using injected O2 and insulation.
95
Why is manifold runner tuning used?
Reduce pressure drop at specific speeds by tuning wave reflections.
96
What powers the turbocharger?
Exhaust gases spin a turbine that drives the compressor.
97
What is turbo lag?
Delay in boost response due to turbine acceleration.
98
How is turbo performance managed?
Bypass valves, ceramics for turbine, and speed-based controls.
99
What is EGR?
Exhaust Gas Recirculation—recycles 15–20% exhaust to intake, reduces temp and emissions.
100
What is the muffler for?
Reduces exhaust sound via absorption and wave cancellation.
101
How does the tailpipe contribute to safety?
Directs gases away from passengers.
102
How does exhaust heating help air-cooled engines?
Can be used for cabin heating—risk if heat exchanger corrodes.
103
How do two-stroke engines handle exhaust?
Use blowdown and pressurized scavenging, with one-way valves to prevent backflow.

ice (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions