Fuels and Combustion
Junior Science
Alkanes
Compounds that contain only carbon and hydrogen are known
as hydrocarbons. Those that contain as many hydrogen atoms as possible are
said to be saturated. The saturated hydrocarbons are also known as alkanes.
Sources of Alkanes
Alkanes are found in petroleum (either crude oil or natural gas). They are formed
by the anaerobic decomposition of marine plant and animal organisms. The main
components in new Zealand natural gas are methane (one carbon alkanes) and
carbon dioxide.
Crude oil is imported into New Zealand from other countries and contains a
mixture of different hydrocarbons with different length carbon chains. The
different chain length hydrocarbons are separated by a process called fractional
distillation as they have different boiling points.
Combustion of Alkanes
Combustion of hydrocarbons involves the breaking of bonds between the
atoms, (as opposed to melting) either with plentiful oxygen – complete
combustion, or limited oxygen – incomplete combustion. The products
formed are water plus CO2 (or CO/C with limited oxygen).
Combustion of Alkanes
Complete combustion
Alkane + Oxygen → Carbon Dioxide + water
Incomplete combustion
Alkane + limited oxygen → Carbon Monoxide or Soot + Water
Combustion
Complete combustion: needs plentiful O2 / good ventilation. Flame burns clear / blue.
The products are CO2 and H2O
Energy efficient - maximum amount of energy in hydrocarbon released
Incomplete combustion:
occurs in limited O2 / poor
ventilation. Flame burns dirty
yellow/orange. The products
CO and C (soot) and H2O.
Reduced energy efficiency –
less than the maximum
amount of energy in
hydrocarbon is released
As C chain length increases you
get more incomplete
combustion occurring as bigger
molecules need more O2 from
complete combustion
complete
incomplete
Combustion equations
Combustion Equations
Step 1. Write down the molecular formula of the alkane plus O2 on the left hand side
Step 2. Write down CO2 plus H2O on the right hand side
Step 3. Add the number of carbon atoms in the Alkane and balance the number of CO2
(same as number of Cs)
Step 4. Add number of Hydrogen atoms in the Alkane and balance the number of H2O
(will be half number of Os)
Step 5. add the total number of Os on the RHS and balance the LHS of O2 (if there is an
uneven number then you can use ½ Os)
Incomplete combustion
For limited oxygen replace CO2 with CO and use same steps
For very limited oxygen replace CO2 with C and use same steps
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Effects of Combustion products on human health and the environment
Carbon Dioxide
Increased levels of Carbon dioxide are linked
to an enhanced greenhouse effect and
global warming leading to climate change.
Climate change has resulted in melting polar
ice and less settled weather as well as
causing different climates that is affecting
animal and plant survival.
Carbon dioxide is a greenhouse gas and traps heat in the atmosphere.
Without it and other greenhouse gases, Earth would be a frozen world
Earth’s climate in 4.5 billion-year has naturally changed between being very cold and
covered in ice, or very hot. In the recent 10,000 years the planet’s climate has become
much more stable, creating an ideal environment for humans and domestication of plants
and animals.
However, over the past 50-100 years, increasing human activity (such as industry,
agriculture and transportation) has begun to affect the natural climate balance. These
activities are increasing the amount of greenhouse gases in our atmosphere and causing
Earth to heat up faster than ever seen before since humans have been on Earth.
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Human activity is increasing the CO2 in the atmosphere and Earth is
becoming a warmer place
Around 1750, the period of
history called the industrial
revolution, humans began to
burn (combust) fossil fuels
and produce carbon dioxide in
increasing amounts. The
overall effect of human
activities on the climate has
been a warming influence.
According to scientific studies,
in the past 650,000 years the
planet has never had so much
carbon dioxide in its
atmosphere as it does today,
and the levels of the gas are
continuing to rise.
Human activity is accelerating climate change
Persistent human
activities like driving
cars, farming and
burning coal in
combustion reactions
produce greenhouse
gases – mainly carbon
dioxide. This gas
gathers in the
atmosphere, wrap
around the earth and
trap the sun's heat.
Human activity is increasing the CO2 in the atmosphere and Earth is
becoming a warmer place
The carbon dioxide and
other greenhouse gases in
the atmosphere act as an
“insulation blanket”. With
not enough greenhouse
gases the heat from the
Sun would reach Earth but
then radiate away leaving
the planet to cold. With
too much greenhouse
gases the heat is trapped
around Earth and doesn’t
escape as easily making
the Earth to hot.
Human activity is accelerating climate change
The more greenhouse
gases we release, the
faster the world's climate
heats up. This process is
called global warming
but it also leads to
climate change because
it is increasing the
amount of floods,
storms, cyclones,
droughts and landslips.
Climate change is
affecting our economy,
environment and the way
we live – we are already
seeing the effects and
need to prepare for more
changes in the future.
Human activity is accelerating climate change
In New Zealand likely climate change impacts include: higher temperatures, more
droughts in some areas and floods in others, and a change in the amount of rain with
higher rainfall in the west and less in the east.
These changes in climate will cause a range of effects including changing agricultural
productivity where some species will not grow as well and other warm loving species will
need to be grown, warmer winters with fewer frosts, but hotter summers causing heat
stress and diseases in plants and animals, rising sea levels will effect coastal areas and
glaciers are expected to retreat.
All living things are made of carbon and that carbon
changes from one form to another in a carbon cycle
Carbon exists in a
number of forms. It is
part of a gas
molecule called
carbon dioxide found
in the atmosphere
which can be turned
into carbon
compounds in plants
through
photosynthesis. This
carbon is then
passed along to
other living
organisms when they
are consumed and
released back into
the atmosphere
during respiration
and combustion
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All living things are made of carbon and that carbon changes from one form
to another in a carbon cycle
Natural processes of photosynthesis and respiration (blue arrows) keep the carbon dioxide
levels reasonably stable in the atmosphere – and therefore the global temperature steady.
Human activity such as farming, industry and burning fossil fuels (red arrows) which have a
large amount of “locked up” carbon are affecting this balance and causing the levels of
Carbon Dioxide to increase.
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Carbon can be stored in the Earth in ‘carbon sinks’ such as fossil fuels, rocks
and ocean sediments
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Effects of Combustion products on human health and the environment
Carbon Monoxide
Carbon Monoxide (CO) is a colourless, odourless, toxic gas that is produced
during incomplete combustion when not enough oxygen is available.
Carbon Monoxide stops haemoglobin in red blood cells carrying oxygen
around body and so a person suffocates.
Effects of Combustion products on human health and the environment
Carbon Monoxide
Effects of Combustion products on human health and the environment
Soot (carbon)
Soot (C) is dirty and polluting.
Soot is produced during
combustion when there is very
limited amounts of oxygen
available. Carbon particles can
cause asthma in some people
and even lung cancer.
Fuels
Fuels are a group of chemicals, mostly alkanes but also alkenes and alcohols, that
humans use by converting the chemical energy stored in the high energy bonds
between carbon and hydrogen into heat and light energy
through the process of combustion. Fuels are used
to heat homes and include coal and oil as well as
for transportation and industry using oil, petrol,
diesel and coal. Other fuels are
processed into plastics.
The Earth has a fixed amount of resources that have to be managed
sustainably
Sustainable means to continue
being able to do something or
use something indefinitely.
Some of our fuels on Earth are
Non-renewable such as coal,
and oil and they will be all
used up eventually as the
process to make more takes a
very long time. Other fuels
such as biofuels are
renewable. As long as we do
not take to much and replace
what we use then these
resources can be used for a
long period of time
sustainably.
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Biomass energy
Biomass relies on the
photosynthetic ability of
plants to convert solar
energy into chemical
energy. The chemical
energy stored in plants is
then broken down by
enzymes and useful
bacteria into biofuels to
be used in machinery.
This type of fuel is
renewable as long as the
same amount of trees are
planted to replace those
cut down. The carbon
dioxide released when
burning the fuels will also
be reabsorbed by the
plants as they grow.
Non-Renewable Energy
Non renewable energy is
energy that comes from the
ground and is able to be not
replaced within a useful
period of time. Fossil fuels
are the main category of
non renewable energy.
Fossil fuels include; coal, oil
and natural gas. These
resources come from
animals and plants that
have died millions of years
ago and then decomposed
to create a useable source
of energy for humans.
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Fossil Fuels - Coal
Coal was formed millions of years ago when plants fell into peat swamps and were
buried by heavy earth and rocks. Over millions of years, the weight of the rocks and heat
in the ground turned the plants into coal.
Most of the world’s coal was formed 300–350 million years ago during the
Carboniferous period that was warm and damp, ideal for plant growth. New Zealand
coals are much younger – they were made 30–70 million years ago and they are a less
energy rich fuel. Coal is mined either underground or in large open cast mines.
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Fossil Fuels – Oil and Gas
Oil and gas were formed
many millions of years ago from
dead sea organisms falling to the sea floor
and being covered by sediment. Over time the
sediment that covered these dead creatures was27 compressed
and formed rock. The carbon and hydrogen atoms that used to be
part of the dead organisms bodies reformed into fuel – the liquid form called oil and the gas
form. Oil and gas are mined by drilling deep into the ground from oil rigs.
The limits of fossil fuels and the unlimited energy of the sun
Fossil fuels are a limited resource. Extraction and mining can be expensive and can
damage the surrounding area. Carbon dioxide gas that is released upon burning the fuels
are contributing to the warming of the climate. Human society has a dependence on fossil
fuels for energy but needs to consider alternative renewable energy sources to replace
decreasing coal, gas and oil supply. Renewable energy is sustainable and in many cases
produces little or no harm to the environment. As new technology develops to collect the
energy it will become cheaper.
Fossil
fuels
Renewable
energy
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Production of fuels – New Zealand Fuels
A fully laden coal train about to leave Seddonville for Westport. (1898)
Due to new Zealand’s geological history and the processes involved to create fossil fuels we do
not have large fields of crude oil (unprocessed oil) but we do have sources of coal (but not the
very black and old high energy coal) and natural gas (mostly methane).
Coal can be used directly by combusting it in power stations such as Huntly to heat water into
steam and power turbines. It is also used in homes for heating. Combusting and mining coal is
very polluting and its use is becoming more limited in New Zealand. Recent disasters (pike river)
in coal mining have also reflected badly on the coal mining industry.
Production of fuels – New Zealand Fuels
Natural gas is extracted at fields around New Zealand, mostly off the coast out at sea, and
this can be further processed into methanol (an alcohol fuel).
We can also produce Ethanol (an alcohol fuel) through the process of fermentation –
anaerobic respiration of yeast.
Above: Kupe Gas platform in Taranaki
Methanol from Natural gas
Producing methanol (an alcohol CH3OH) from
Natural gas (an alkane CH4) is a three step process.
(i) Steam reforming where methane reacts with
steam
CH4 + H2O → CO + 3H2
(iii) Synthesis reaction
2H2 + CO → CH3OH
Methanol is used to make other chemicals that are
used in making paints, plastics and explosives and
in methylated sprits
(ii) Water shift reaction – a
reaction that adjusts
the ratio of CO: H2 gas
Fermentation to produce fuel (ethanol)
Fermentation is anaerobic respiration. Enzymes in yeast turn sugar solution (eg
glucose) into ethanol and carbon dioxide (in the absence of oxygen).
C6H12O6 →
Glucose
CO2
+
carbon dioxide
CH3CH2OH
ethanol
Production of fuels – imported Fuels
New Zealand needs to
import crude oil from
other countries and then
further refine it (or process
it) into other types such as
petrol, diesel and motor oil
in order to provide fuel for
our cars, trucks and
industries.
These processes of refining
include fractional
distillation to separate out
the mixed length carbon
chain alkanes into distinct
types of fuel as well as
cracking which breaks the
long carbon chained
alkanes into shorter, more
useful fuels.
Fractional distillation of crude oil
Fractional column
Coolest at the top, gases
(Carbon chains 1 – 4) collected
at the top – they have the
lowest boiling points which is
why they don’t condense – they
stay as gases
Cooler as you go up, smaller
molecules condense higher up
as they have lower boiling
points
Hottest at bottom. Large
molecules condense here as
have highest boiling points
Fractional distillation of crude oil
Different hydrocarbons and their boiling points
Petroleum Gas - Used for heating, cooking, and making plastics
-small alkanes (1 to 4 carbon atoms)
-commonly known by the names methane, ethane, propane, butane
-boiling range = less than 104 degrees Fahrenheit / 40 degrees Celsius
-often liquified under pressure to create LPG (liquified petroleum gas)
Naphtha - intermediate that will be further processed to make gasoline
-mix of 5 to 9 carbon atom alkanes
-boiling range = 140 to 212 degrees Fahrenheit / 60 to 100 degrees
Celsius
Gasoline - motor fuel
-liquid
-mix of alkanes and cycloalkanes (5 to 12 carbon atoms)
-boiling range = 104 to 401 degrees Fahrenheit / 40 to 205 degrees Celsius *
Kerosene - fuel for jet engines and tractors; starting materials for making other
products
-liquid
-mix of alkanes (10 to 18 carbons) and aromatics
-boiling range = 350 to 617 degrees Fahrenheit / 175 to 325 degrees Celsius *
Different hydrocarbons and their boiling points
Gas oil - used for diesel fuel and heating oil; starting material for making other products
-liquid
-alkanes containing 12 or more carbon atoms
-boiling range = 482 to 662 degrees Fahrenheit / 250 to 350 degrees Celsius *
Lubricating oil - used for motor oil, grease, other lubricants
-liquid
-long chain (20 to 50 carbon atoms) alkanes, cycloalkanes, aromatics
-boiling range = 572 to 700 degrees Fahrenheit / 300 to 370 degrees Celsius *
Heavy gas or fuel oil - used for industrial fuel; starting material for other
products
-liquid
-long chain (20 to 70 carbon atoms) alkanes, cycloalkanes, aromatics
-boiling range = 700 to 1112 degrees Fahrenheit / 370 to 600 degrees Celsius *
Residuals - coke, asphalt, tar, waxes; starting material for other products
-solid
-multiple-ringed compounds with 70 or more carbon atoms
-boiling range = greater than 1112 degrees Fahrenheit / 600 degrees Celsius
Cracking of fractions
The cracking process uses heat and/or catalyst to break long less useful alkenes e.g.
naptha fraction, into smaller more useful ones such as to make petrol or to make
ethene (that can be made into plastics)
Temp, pressure, catalyst
C10H22 ---------------------- C8H18 + C2H4
Long hydrocarbon chain
alkane + alkene