Combustion

Energy

• Everything in the world runs on energy• The Earth needs the sun’s energy for light and

warmth• We need energy from the food we eat• Cars and furnaces run on energy from burning

fossil fuels

Fossil Fuels

• Plants use the sun for energy through photosynthesis

• After these plants die, their remains accumulate on the Earth’s surface

• In some areas, these remains accumulate in thick layers and are covered by rock and soil over time

• Pressure over time converts these layers into fossil fuels (coal, petroleum, natural gas), or fuels made from fossilized organic material

Fossil Fuels (Cont)

• The energy from the sun is still trapped in these fossil fuels

• Through combustion (or burning) of these fossil fuels, we can release that energy

• The fossil fuels we use in industrial combustion are called hydrocarbons

Types of Hydrocarbons

What is combustion

• Combustion = Burning• Combustion can either be complete or incomplete• Examples of combustion– Burning a candle– Burning wood in a fire place– Igniting a gas burner on a stove or grill– Burning coal in a power plant– Burning fuel in an automobile’s engine– Burning of glucose in the human body (cellular

respiration)

Combustion in a fuel tank

Complete Combustion

• Usually occurs when a hydrocarbon reacts with oxygen to produce carbon dioxide and water vapor

• Combustion is EXOTHERMIC (releases heat)• Hydrocarbon + Oxygen Carbon dioxide +

water • Hydrocarbon + O2 CO2 + H2O

Examples of Combustion reactions

• Methane• CH4 +2O2 -> CO2 +2H2O

• Naphthalene• C10H4 +12O2 -> 10CO2 + 4H2O

• Ethane• 2C2H6 + 7O2 -> 4CO2 + 6H20

Incomplete combustion

• Complete combustion needs ample amounts of oxygen

• With insufficient oxygen present, the result is incomplete combustion

• Complete combustion produces Carbon dioxide (CO2)• Incomplete combustion produces Carbon Monoxide

(CO) – a very dangerous gas• Incomplete combustion can also produce solid

Carbon

Example of Incomplete Combustion

• CH4(g) + 1.5 O2(g) → CO(g) + 2 H2O(g)

The product of this example is Carbon Monoxide

• CH4(g) + 1 O2(g) → C(s) + 2 H2O(g)

The product of this example is solid Carbon

Effects of incomplete combustion

• In a perfect world, automobiles would completely combust their fuel, or hydrocarbons(a combinations of hydrogens and carbons).

• Hydrocarbons would enter an engine, along with nitrogen and oxygen. The pressure in the engine’s internal combustion chamber would cause it to burn (or combust)

• All the of the hydrogens would turn into water, all the carbons into carbon dioxide, and the nitrogens remain unchanged

FUEL (hydrocarbons) + AIR (oxygen and nitrogen) = CARBON DIOXIDE (CO2) + Water (H2O) + Nitrogen

Effects of incomplete combustion

• The world is not perfect however, and automobile combustion is usually imcomplete

• Some of the oxygen reacts with the nitrogen creating Nitrous Oxides (NOx), while the rest of the oxygen reacts with the carbon, forming Carbon Monoxide instead of Carbon dioxide, along with the unburned fuel, or volitile organic compounds (VOCs)

(see next slide for reaction)

Effects of Incomplete combustion

• Incomplete auto combustion reactionFUEL (hydrocarbons) + AIR (oxygen and nitrogen) = UNBURNED or PARTIALLY BURNED HYDROCARBONS (VOCs) + NITROGEN OXIDES (NOx) + CARBON MONOXIDE (CO) + CARBON DIOXIDE (CO2) + Water (H2O)

• Sound familiar? Remember the products of smog? Incomplete auto combustion creates smog!!!

Solutions? Alternatives?

• 1970 – The Clean Air Act was passed• I975 – Catalysts were put into car engines to

reduce hydrocarbon and carbon monoxide emissions

• 1980-81 – More sophisticated Catalysts not only reduced emissions, but converted carbon monoxide and unburned hydrocarbons (VOCs )to carbon dioxide and water and also changed Nitrogen Oxides to elemental Nitrogen and Oxygen. Why it’s called a Catalytic Converter

Solutions? Alternatives?

• 1990 – The Clean Air Act now required manufacturers to further reduce vehicle emissions

• 2004 – EPA’s tier 2 emission standards require that all new vehicles receive a 96-99% in emissions, effectively eliminating almost all pollutants from today’s vehicles.

• Now – hybrid cars that use less fuel are becoming more common and even fully electronic cars are being developed.