BURNING FUELS Noadswood Science, 2011

Burning Fuels To know the processes involved with burning fuels Monday, May 11, 2015

Steam Why do cars produce steam from their exhaust (most noticeable on cold days)? The internal combustion engine produces water as a product – visible from the exhaust as water vapour…

Combustion Combustion is the chemical reaction which takes place when a substance burns The substance reacts with oxygen, releasing energy (heat and light) Combustion is extremely important (>90% of the world’s energy comes from combustion reactions (e.g. fossil fuels such as coal, natural gas and petrol) What is needed for combustion to take place? Heat Fuel Oxygen

Combustion Combustion is exothermic - heat is released to the surroundings This can also be called an oxidation reaction, as it involves oxygen being added to the fuel – the carbon and hydrogen in the fuels are oxidised The fuel you use will result in different combustion reactions taking place…

Combustion Demo Watch the demo of complete combustion Methane is our fuel: - methane + oxygen  carbon dioxide + water CH 4 + 2O 2  CO 2 + 2H 2 O

Complete & Incomplete A good supply of oxygen is needed for a fuel to burn completely and release as much energy as possible If there is a plentiful supply of oxygen we get complete combustion However, if there is not enough oxygen then the fuel will not burn completely, wasting both the fuel and reducing the energy released If there is not enough oxygen we get incomplete combustion Complete combustion carbon + oxygen  carbon dioxide Incomplete combustion carbon + oxygen  carbon monoxide

Complete & Incomplete Complete and incomplete combustion can be shown clearly using the Bunsen burners – when the air inlet is open plenty of oxygen is available to the fuel allowing it to burn completely (blue roaring flame) When partially or fully closed the oxygen supply is limited, and the yellow safety flame is shown which is a result of incomplete combustion (soot is very prominent product)

Complete & Incomplete Complete the combustion of methane equations in low and high oxygen environments (word and symbol)… *During complete combustion one reaction occurs producing two products *During incomplete combustion two reactions occur, both producing two products **Symbol equation for methane is CH 4

Complete Combustion In normal air (high oxygen) one chemical reactions takes place during the complete combustion: - Methane + Oxygen  Carbon Dioxide + Water CH 4 + 2O 2  CO 2 + 2H 2 O

Incomplete Combustion In low oxygen two chemical reactions take place during the incomplete combustion: - Methane + Oxygen  Carbon Monoxide + Water 2CH 4 + 3O 2  2CO + 4H 2 O Methane + Oxygen  Carbon + Water CH 4 + O 2  C + 2H 2 O

Fuels Many fuels are hydrocarbons - made up of hydrogen and carbon – when they burn they produce carbon dioxide and water Methane + Oxygen  Carbon Dioxide + Water Petrol is a complex mix of hydrocarbons, with an important component being 2,2,4-Trimethylpentane (isooctane) However as it is a hydrocarbon the equation above still applies, resulting in carbon dioxide and water being produced during the combustion (along with a few other products such as nitrogen oxides, sulfur, some un-combusted hydrocarbons and soot (particulate matter))

Experiment In groups you will be given 4x different spirit burners containing unknown fuels – how could you set up an experiment to identify which fuel is which? The only information given to you is the energy found within the different fuels: - ▫Methane = 50 MJ per kg ▫Ethane = 48 MJ per kg ▫Propane = 46 MJ per kg ▫Butane = 45 MJ per kg ▫*Hydrogen = 142 MJ per kg ▫*Petrol = 47 MJ per kg

Experiment We can use the small burners of the different fuels to heat some water for a known period of time – we should find that the water reaches a higher temperature when heated with the fuel which releases the most amount of energy (i.e. methane) Remember, keep the time of heating, amount of water, distance between the heater and water; type of water; amount of fuel etc… the same to ensure this is a fair and reliable experiment!