Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MECH 453 > Section 7 - IC Engine Exhaust Emissions > Flashcards

Section 7 - IC Engine Exhaust Emissions Flashcards

1
Q

What emissions do hydrogen fuelled engines produce?

A

NOx

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

Emissions of concern are:

A
  1. Unburned HCs
  2. CO
  3. NOx (nitric oxide and nitrogen dioxide)
  4. SO2
  5. Solid carbon particulates
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

HC emissions include:

A
  • Benzene
  • Polycyclic aromatic HCs
  • Three aldehydes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why is LA prone to emissions? (5)

A
  • Unique geography in the basin
  • Pacific Ocean (west) breeze always blows inland
  • Mountain ranges surround the basin
  • Population is huge, everyone loves cars
  • Emissions are trapped in the basin, and it sits endlessly to cook
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Classic smog vs. Photochemical smog

A

Classic: mix of smoke and SO2
Photochemical: chemical rxn of sunlight, NOx and HC in lower troposphere (airborne particules and ground-lvl ozone)

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

2 ways to combat growing emissions

A
  1. Make cars more fuel efficient
  2. Clean up emissions that are sent out the exhaust pipe
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why did we introduce regulation for particulate matter?

A

Direct injection (prior to 2009, all gas engines were port injection, so whatever got into the cylinder was perfect stoichiometric mix)

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

T/F: Sulfur facilitates the operation of the catalytic converter in the exhaust

A

F: Sulfur is a poison and coats the catalyst, preventing it from working

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

Tier 3 regulation tightened sulfur limit for gas to ___ ppm

A

10

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

Ontario drive clean program

A

In Ontario, every vehicle was required to perform a tail pipe emission test every other year to check compliance with emission regulations

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

What is the dominant component of NOx in SI engines?

A

NO

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

NO and equilibrium conditions

A

If [NO] is lower than equilibrium value, NO forms

If [NO] is higher than equilibrium value, NO decomposes

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

T/F: Peak NO concentrations coincide with highest adiabatic flame temperature

A

F: Peak No concentrations occur for slightly lean mixtures corresponding to lower AFT but higher oxygen concentration

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

Measures taken to reduce AFT will also reduce NO, such as:

A
  • Increased residual gas fraction
  • Exhaust gas recirculation (EGR)
  • Moisture in the inlet air
  • Run fuel lean
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

HC cause a decrease in ________ efficiency

A

Thermal

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

6 mechanisms responsible for HC emissions:

A
  1. Crevices
  2. Oil layers
  3. Deposits
  4. Liquid fuel
  5. Flame quench
  6. Exhaust valve leakage
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Crevices

A

Narrow regions of combustion chamber into which flame cannot propagate (smaller than quenching distance)

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

Oil layers

A

Piston ring is not 100% effective in preventing oil migration into the cylinder above the piston, so an oil layer in the combustion chamber traps fuel

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

Deposits

A

Build up on valves, cylinder and piston crown. porous with pore sizes smaller than quenching distance.

20
Q

Liquid fuel

A

Less volatile constituents may not vaporize (especially during engine warm-up) and be absorbed by crevices or deposits.

21
Q

Flame quenching

A

Flame does not burn completely to the internal surfaces. Extinguishes at a small but finite distance from the wall

22
Q

What happens with the hydrocarbons during exhaust?

A

Hydrocarbons rush out of cylinder twice: first time when exhaust opens (vortex forms) and second time when piston pushes it up

23
Q

Longer ignition delay leads to:

A
  • Longer fuel has to mix –> volume becomes larger, knock is introduced
  • Larger unburned HCs
24
Q

Positive Crankcase Ventilation (PCV)

A

First emission control system that directs crankcase gases into the air intake stream so they are consumed during normal in-cylinder combustion. PCV valve includes a spring and uses the intake manifold vacuum to control the flow of gases. Included a device that routed the oil from the crankcase gases to return to the crank case

25
Q

Particulates are classified as:

A
  1. Solid carbon material (soot)
  2. Condensed HCs and their partial oxidation products
26
Q

The critical C/O ratio for onset of soot formation is ___ to ___.

A

0.5 to 0.8

27
Q

Any carbon not oxidized in the culinder ends up as ______ in the ______

A

Soot, exhaust

28
Q

T/F: Diesel engine, by default, will produce more power than gas engine even if the fuel has the same E content

A

F: will produce LESS power than gas engine

29
Q

What happens to the creation/consumption of soot when we reduce the AFT to reduce NOx (in a diesel engine)?

A

Reducing AFT > decreases amnt of soot that is oxidized > increases amnt of soot in the exhaust

30
Q

Carbon monoxide appears in the exhaust of _____ _____ running engine

A

Fuel rich

31
Q

T/F: In practice, it is often assumed the C-O-H system is in equilibrium until the exhaust valve opens at which time it freezes instantaneously

A

T

32
Q

T/F: The highest CO emission occurs during engine warm up when the engine is run fuel rich to compensate for poor fuel evaporation

A

T

33
Q

3 basic methods used to control engine emissions

A
  1. Engineering of combustion process (advances in fuel injectors, O2 sensors, and ECUs)
  2. Optimizing the choice of operating parameters (2 measures currently spark retard and EGR)
  3. After treatment devices in the exhaust system (catalytic converter)
34
Q

Catalytic converter

A

Uses a reduction catalyst followed by an oxidation catalyst to remove Co, No, and HC

35
Q

Metals in catalytic converter

A

Platinum, rhodium, and/or palladium

36
Q

Three-way catalytic converter

A

Begins with reduction catalyst, where platinum and rhodium removes NOx (produces O2 and N2)

Second stage occurs when platinum and palladium oxidizes CO and unburned HCs using the O2 produced in 1st stage

37
Q

T/F: Three-way cat converter will function properly only if the exhaust gas composition corresponds to roughly stoichiometric combustion, and the temperature of the gases is high

A

T

38
Q

Light-off temperature

A

Temp at which converter becomes 50% efficient

39
Q

Emission control sensor (3)

A
  • At the exhaust (before cat converter) used to control fuel delivery so A/F ratio is near stoichiometric (feedback)
  • When hot, produces voltage that varies according to amnt of O2 in exhaust
  • Output is nonlinear (0.2 VDC to 0.8 VDC, lean to rich)
40
Q

Why are 3-way catalytic converters not useful for a diesel engine? What’s used instead?

A

Fuel runs lean in diesels. Oxidizer catalysts are used for reducing HC and CO, and Diesel Particulate Filters (DPFs) are used for removing PM

41
Q

Active Diesel Particulate Filters (DPFs)

A

Raise temp of filter by periodically adding fuel to exhaust stream that combusts in the filter, raising DPF temp. Cleans the DPF by oxidizing the collected PM with O2

42
Q

Exhaust gas recirculation (EGR) for NOx control

A

Low P: injection of exhaust gases into low P part of intake

High P: injecting exhausts into high P part of intake

43
Q

2 recent approaches to diesel exhaust treatment:

A
  1. NOx absorber catalysts (NOx trap)
  2. Selective catalytic reduction (SCR)
44
Q

NOx traps (3)

A
  • Have been used on light-duty vehicles
  • Lean operation, NOx is adsorbed into porous material and every min extra diesel is added
  • NOx is desorbed and consumed using a reduction catalyst that is effective under rich cond’ts IOT combust rich to form CO
45
Q

Selective Catalytic Reduction (SCR) (2)

A
  • Reductant ammonia is used to enable conversion of NO2 to N2 and H2O
  • Aqueous sol’n of urea (NH2)2CO is added to exhaust stream to produce ammonia

MECH 453 (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions