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developing fuels > DF 10 - the trouble with emissions > Flashcards

DF 10 - the trouble with emissions Flashcards

specification reference - (k) (n)

1
Q

what goes and comes out of a car engine

A

fuel goes into a car engine and CO2, CO, H2O, unburnt hydrocarbons, nitrogen, NOx and SOx and particulates come out of a car engine

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2
Q

what is NOx, SOx, and CxHy

A

NOx - oxides of nitrogen
SOx - oxides of sulfur
CxHy - various hydrocarbons

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3
Q

what is evaporative emission

A

vaporized fuel being emitted into the atmosphere from the fuel system of a motor vehicle.

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4
Q

how much does evaporative emission account for the emissions of volatile organic compounds from petrol vehicles

A

10%

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5
Q

where do the oxides of sulfur come from in vehicle exhausts

A

comes from sulfur compounds in the fuel. these combine with the oxygen from the air in heat of the engine

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6
Q

where do the oxides of nitrogen come from

A

they’re formed mainly from the components of the air itself. at the high temperatures in vehicle engines, nitrogen and oxygen react in the air to form nitrogen oxide. some of this reacts with more oxygen to form nitrogen oxide

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7
Q

why do NOx and SOx give rise to acid rain

A

they’re both acidic

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8
Q

what does acid rain do

A

causes health problems, corrodes limestone buildings and damages forests and lakes

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9
Q

how is carbon monoxide formed

A

by the incomplete combustion of hydrocarbon fuels.

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10
Q

what is the problem with carbon monoxide

A

it is very toxic to humans and is oxidised to carbon dioxide in the atmosphere

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11
Q

what are particulates

A

small carbon particles not visible to naked eye that can get into our lungs and cause irritation and disease. they are also produced by the incomplete combustion of the hydrocarbon fuels in diesel

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12
Q

why is ozone a secondary pollutant

A

it is not released directly into the atmosphere.

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13
Q

how is ozone formed

A

from chemical reactions that occur when sunlight shines on a mixture of primary pollutants, oxygen and water vapour

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14
Q

give examples of primary pollutants

A

nitrogen oxides and hydrocarbons

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15
Q

what is the difference between a primary and secondary pollutant

A

A primary pollutant is an air pollutant emitted directly from a source. A secondary pollutant is not directly emitted as such, but forms when other pollutants (primary pollutants) react in the atmosphere.

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16
Q

what is photochemical smog

A

haze in the atmosphere accompanied by high levels of ozone and nitrogen oxides, caused by the action of sunlight on pollutants.

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17
Q

when does a photochemical reaction occur

A

when a molecule absorbs light energy and then undergoes a chemical reaction

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18
Q

what reactions occur in photochemical smogs

A

other irritating compounds are formed by the breakdown and further reactions of the hydrocarbons

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19
Q

what is the problems with ozone

A

it can be an irritating toxic gas and high concentrations near ground level are damaging to human health. it weakens the body’s immune system and attacks lung tissue

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20
Q

how does ozone contribute to global warming

A

it acts as a greenhouse gas

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21
Q

what does the composition of primary and secondary pollutants in ozone depend on

A

the nature of the primary pollutants, weather conditions, time of day and length of smog

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22
Q

when do photochemical smogs normally occur

A

in the summer during high pressure (anticyclonic) conditions

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23
Q

what do photochemical smogs cause

A

haziness and reduced visibility in the air close to the ground. it can cause eye and nose irritation and some difficulty in breathing. in vulnerable groups such as asthmatics who already have respiratory problems and many older people, this effect can be enhanced

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24
Q

how can high ozone concentrations affect plants and animals

A

ozone is a highly reactive substance that attacks most organic matter. compounds with carbon-carbon double bonds are particularly vulnerable so many materials such as plastics, rubbers, textiles and paints can be damaged

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25
Q

what do the products of combustion depend on

A

the amount of oxygen available

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26
Q

what is the equation for complete combustion (in a plentiful supply of air/oxygen)

A

hydrocarbon + oxygen —> carbon dioxide + water

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27
Q

what is the equation for incomplete combustion (in a limited supply of air/oxygen)

A

hydrocarbon +oxygen (limited) —> carbon + carbon monoxide + water

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28
Q

give a balanced equation for the complete combustion of heptane

A

C7H16 + 11O2 —> 7CO2 + 8H2O

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29
Q

what else can be used as fuels

A

alcohols

30
Q

what does the burning of sulfur compounds produce

A

sulfur dioxide
S + O2 —-> SO2

31
Q

how do nitrogen and oxygen react to form nitrous oxide

A

nitrogen and oxygen in the air react in the high temperatures of the vehicle engines
N2 + O2 —> 2NO

32
Q

how are other nitrogen oxides formed

A

by burning nitrogen compounds in fuels but these are present in very low proportions especially in vehicle fuels

33
Q

what is a key fact to note about NOx and SOx

A

the sulfur is present in the fuel but the nitrogen isn’t

34
Q

how is sulfuric acid formed

A

sulfur dioxide reacts with water in the atmosphere to form sulfuric acid, a weak acid
SO2 + H2O —> H2SO4

35
Q

how is sulfur dioxide oxidised to sulfur trioxide

A

it occurs in the stratosphere. the sulfur trioxide then reacts with water in the atmosphere to form sulfuric acid, a strong acid
SO3 + H2O —-> H2SO4

36
Q

how is nitric acid formed

A

nitrogen oxide and nitrogen dioxide react with water and oxygen in the atmosphere to form nitric acid, a strong acid
2NO + H2O + 1 1/2O2 —-> 2HNO3
2NO + H2O + 1/2 O2 —-> 2HNO3

37
Q

what is the major source and polluting effects of particulates

A

major sources - volcanoes, burning fuels and burning coal
polluting effects - penetrate deep into the human body causing heart attacks and lung cancer

38
Q

what is the major source and polluting effect of volatile organic compounds

A

major sources - plants, unburnt fuels from petrol vehicles
polluting effects - photochemical smog

39
Q

what is the major source and polluting effect of carbon monoxide

A

major sources - incomplete combustion of hydrocarbons in fossil fuels, burning biomass
polluting effects - toxic gas, photochemical smog

40
Q

what is the major source and polluting effect of carbon dioxide

A

major sources - combustion of fossil fuels
polluting effect - greenhouse effect

41
Q

what is the major source and polluting effect of nitrogen oxides

A

major sources - combustion of fuels in power stations and vehicles
polluting effect - acid rain, photochemical smog

42
Q

what is the major source and polluting effect of sulfur oxides

A

major sources - volcanoes, burning of fuels containing sulfur
polluting effect - toxic gas and acid rain

43
Q

how can we tackle the problems of emission

A

one involves changing the design of the car and the other involves changing the fuel used by the car.
also we can limit the traffic entering towns and encouraging car sharing schemes of tackling the problems directly

44
Q

which 3 reactions naturally occur to convert pollutants into carbon dioxide, water and nitrogen

A

1) using oxygen to turn carbon monoxide to carbon dioxide
2) using oxygen to turn hydrocarbons to carbon dioxide and water
3) reacting nitrogen oxide with carbon monoxide to form carbon dioxide and nitrogen

45
Q

why is the way that pollutants are converted a problem

A

the reactions that convert pollutants into carbon dioxide, water and nitrogen all occur naturally. however, under the conditions inside an exhaust system they go too slowly to get rid of the pollutants

46
Q

what are catalytic converters

A

they are in petrol cars and contain catalysts of platinum or rhodium on a honeycomb structure

47
Q

what do catalytic converters do

A

they speed up the 3 reactions that convert the pollutants into less harmful products

48
Q

what is another name for a catalytic converter

A

a 3-way catalysts as they speed up the 3 reactions that convert pollutants

49
Q

when do catalytic converters only work

A

if the air-petrol mixture is carefully controlled so that it is exactly the stoichiometric mixture for the fuel

50
Q

what does it mean by the “stoichiometric mixture of the fuel”

A

it has the exact calculated ratio of hydrocarbon to oxygen needed for complete combustion

51
Q

what would happen if the air-petrol mixture inside a car had too much fuel

A

there is not enough oxygen in the exhaust fumes to remove carbon monoxide and the hydrocarbons

52
Q

what do cars fitted with 3-way catalyst systems need to have

A

oxygen sensors in the exhaust gases, linked back to electronically controlled fuel injection systems

53
Q

when do catalytic converters work

A

when they are hot

54
Q

at what temperature do platinum catalysts start working at

A

around 240° but you can get the catalyst to start working at around 150° by alloying the platinum with rhodium

55
Q

why can converters only be used with free-lead fuel

A

because the catalysts are poisoned with lead

56
Q

how is the catalyst given a large surface area

A

its used in the form of a fine powder spread over a ceramic support with a surface that has a network of tiny holes

57
Q

why would any attempt to reduce NOx to nitrogen in a diesel engine fail

A

diesel engines have a higher concentration of oxygen so any attempt to reduce NOx to nitrogen would fail as the reducing agent would be oxidised by the oxygen

58
Q

what do diesel engines have to overcome this problem

A

they have oxidation catalysts that turn carbon monoxide to carbon dioxide and hydrocarbons to carbon dioxide and water

59
Q

how have the amount of particulates in diesel exhaust gases been reduced

A

by burning them at high temperatures

60
Q

what is the problem with burning particulates at high temperatures to get rid of them

A

it reduces fuel efficiency

61
Q

what are the main pollutants in petrol engines

A

carbon monoxide, hydrocarbons and nitrogen monoxide

62
Q

what are the pollutants in petrol engines converted to

A

carbon monoxide
2CO + O2 —> 2CO2
hydrocarbons
C7H16 + 11O2 —-> 7CO2 + 8H2O
nitrogen monoxide
2NO + CO —–> N2 + 2CO2

63
Q

what catalyst converts the pollutants in a petrol engine

A

platinum or rhodium in a porous support

64
Q

how are sulfur oxide pollutants best avoided in petrol engines

A

by removing sulfur impurities from the fuels before being made available to the motorist

65
Q

what are the main pollutants in diesel engines and how are they removed

A

carbon monoxide, hydrocarbons, particulates and nitrogen oxide compounds.
CO and CxHy are removed in the same way as in petrol engines
particulates are removed by diesel particulate filters that contain a variety of materials, most commonly ceramic

66
Q

what is regeneration in a catalyst

A

burning off the carbon particles

67
Q

how is regeneration of a catalyst accomplised

A

by increasing the temperatures at times decided by the vehicles computer. this increases fuel consumption

68
Q

how are nitrogen oxides reduced in a diesel engine

A

by recycling some of the exhaust gases through the cylinder, lowering the temperature and thus the amount of NOx formed.

69
Q

what is an alternative to reduce NOx in diesel engines

A

alternatively a reagent such as ammonia is used in the presense of a catalyst
4NO + 4NH3 + O2 —> 4N2 + 6H2O

70
Q

how is SOx reduced in diesel engines

A

sulfur dioxide is best avoided in the first place by using ultra low sulfur fuels

developing fuels (11 decks)

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