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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
what do the products of combustion depend on
the amount of oxygen available
26
what is the equation for complete combustion (in a plentiful supply of air/oxygen)
hydrocarbon + oxygen ---> carbon dioxide + water
27
what is the equation for incomplete combustion (in a limited supply of air/oxygen)
hydrocarbon +oxygen (limited) ---> carbon + carbon monoxide + water
28
give a balanced equation for the complete combustion of heptane
C7H16 + 11O2 ---> 7CO2 + 8H2O
29
what else can be used as fuels
alcohols
30
what does the burning of sulfur compounds produce
sulfur dioxide S + O2 ----> SO2
31
how do nitrogen and oxygen react to form nitrous oxide
nitrogen and oxygen in the air react in the high temperatures of the vehicle engines N2 + O2 ---> 2NO
32
how are other nitrogen oxides formed
by burning nitrogen compounds in fuels but these are present in very low proportions especially in vehicle fuels
33
what is a key fact to note about NOx and SOx
the sulfur is present in the fuel but the nitrogen isn't
34
how is sulfuric acid formed
sulfur dioxide reacts with water in the atmosphere to form sulfuric acid, a weak acid SO2 + H2O ---> H2SO4
35
how is sulfur dioxide oxidised to sulfur trioxide
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
how is nitric acid formed
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
what is the major source and polluting effects of particulates
major sources - volcanoes, burning fuels and burning coal polluting effects - penetrate deep into the human body causing heart attacks and lung cancer
38
what is the major source and polluting effect of volatile organic compounds
major sources - plants, unburnt fuels from petrol vehicles polluting effects - photochemical smog
39
what is the major source and polluting effect of carbon monoxide
major sources - incomplete combustion of hydrocarbons in fossil fuels, burning biomass polluting effects - toxic gas, photochemical smog
40
what is the major source and polluting effect of carbon dioxide
major sources - combustion of fossil fuels polluting effect - greenhouse effect
41
what is the major source and polluting effect of nitrogen oxides
major sources - combustion of fuels in power stations and vehicles polluting effect - acid rain, photochemical smog
42
what is the major source and polluting effect of sulfur oxides
major sources - volcanoes, burning of fuels containing sulfur polluting effect - toxic gas and acid rain
43
how can we tackle the problems of emission
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
which 3 reactions naturally occur to convert pollutants into carbon dioxide, water and nitrogen
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
why is the way that pollutants are converted a problem
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
what are catalytic converters
they are in petrol cars and contain catalysts of platinum or rhodium on a honeycomb structure
47
what do catalytic converters do
they speed up the 3 reactions that convert the pollutants into less harmful products
48
what is another name for a catalytic converter
a 3-way catalysts as they speed up the 3 reactions that convert pollutants
49
when do catalytic converters only work
if the air-petrol mixture is carefully controlled so that it is exactly the stoichiometric mixture for the fuel
50
what does it mean by the "stoichiometric mixture of the fuel"
it has the exact calculated ratio of hydrocarbon to oxygen needed for complete combustion
51
what would happen if the air-petrol mixture inside a car had too much fuel
there is not enough oxygen in the exhaust fumes to remove carbon monoxide and the hydrocarbons
52
what do cars fitted with 3-way catalyst systems need to have
oxygen sensors in the exhaust gases, linked back to electronically controlled fuel injection systems
53
when do catalytic converters work
when they are hot
54
at what temperature do platinum catalysts start working at
around 240° but you can get the catalyst to start working at around 150° by alloying the platinum with rhodium
55
why can converters only be used with free-lead fuel
because the catalysts are poisoned with lead
56
how is the catalyst given a large surface area
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
why would any attempt to reduce NOx to nitrogen in a diesel engine fail
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
what do diesel engines have to overcome this problem
they have oxidation catalysts that turn carbon monoxide to carbon dioxide and hydrocarbons to carbon dioxide and water
59
how have the amount of particulates in diesel exhaust gases been reduced
by burning them at high temperatures
60
what is the problem with burning particulates at high temperatures to get rid of them
it reduces fuel efficiency
61
what are the main pollutants in petrol engines
carbon monoxide, hydrocarbons and nitrogen monoxide
62
what are the pollutants in petrol engines converted to
carbon monoxide 2CO + O2 ---> 2CO2 hydrocarbons C7H16 + 11O2 ----> 7CO2 + 8H2O nitrogen monoxide 2NO + CO -----> N2 + 2CO2
63
what catalyst converts the pollutants in a petrol engine
platinum or rhodium in a porous support
64
how are sulfur oxide pollutants best avoided in petrol engines
by removing sulfur impurities from the fuels before being made available to the motorist
65
what are the main pollutants in diesel engines and how are they removed
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
what is regeneration in a catalyst
burning off the carbon particles
67
how is regeneration of a catalyst accomplised
by increasing the temperatures at times decided by the vehicles computer. this increases fuel consumption
68
how are nitrogen oxides reduced in a diesel engine
by recycling some of the exhaust gases through the cylinder, lowering the temperature and thus the amount of NOx formed.
69
what is an alternative to reduce NOx in diesel engines
alternatively a reagent such as ammonia is used in the presense of a catalyst 4NO + 4NH3 + O2 ---> 4N2 + 6H2O
70
how is SOx reduced in diesel engines
sulfur dioxide is best avoided in the first place by using ultra low sulfur fuels

developing fuels (11 decks)

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