How Things Change/React With One Another
A combustion reaction is a major class of chemical reactions, commonly referred to as "burning". Combustion usually occurs when a hydrocarbon reacts with oxygen to produce carbon dioxide and water. In the more general sense, combustion involves a reaction between any combustible material and an oxidizer to form an oxidized product. Combustion is an exothermic reaction, so it releases heat, but sometimes the reaction proceeds so slowly that a temperature change is not noticeable.
Good signs that you are dealing with a combustion reaction include the presence of oxygen as a reactant and carbon dioxide, water and heat as products. Inorganic combustion reactions might not form all of the products but are recognizable by the reaction of oxygen.
Combustion doesn't always result in fire, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g., but using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining.
The general form of a combustion reaction
Hydrocarbon + oxygen → carbon di-oxide + water
Complete versus incomplete combustion
Combustion, like all chemical reactions, does not always proceed with 100% efficiency. It is prone to limiting reactants that same as other processes. So, there are two types of combustion you are likely to encounter:
- Complete Combustion - Also called "clean combustion", clean combustion is oxidation of a hydrocarbon that produces only carbon dioxide and water. An example of clean combustion is burning of candle wax, where the heat from the wick vaporizes wax (a hydrocarbon), which reacts with oxygen in the air to release carbon dioxide and water. Ideally, all the wax burns so nothing remains once the candle is consumed. The water vapour and carbon dioxide dissipate into the air.
- Incomplete Combustion - Also called "dirty combustion", incomplete combustion is hydrocarbon oxidation that produces carbon monoxide in addition to carbon dioxide. An example of incomplete combustion would be burning coal, where a lot of soot and carbon monoxide is released. Many of the fossil fuels burning incompletely, releasing waste products.
Fuel Efficiency: How Efficient Are Fossil Fuels?
As we all knew that the energy can neither be created nor destroyed. Efficiency is basically the measure of the amount of an energy converted to another form. Basically, fuel efficiency can be defined as the efficiency of the process in which thermal energy given to the fuel converts the chemical potential energy of fuel to kinetic energy.
The efficiency of all the fuels varies with the device. In terms of the economy also, the efficiency of the fuel depends upon the energy efficiency of a particular device. The efficiency of fuels is measured in kilometres per litre in India, miles per gallon (mpg) in the U.S. and there are other measurement systems for different countries based on their standard units of use for the measurement of efficiency.
Coal is responsible for 41% of world’s electricity generation. The overall efficiency of a coal power plant is 32% to 42%.
For example, let us take an example of two fuels: Gasoline and diesel oil and see why it differs in efficiency and cost.
We see that people choose diesel not gasoline since it saves money. Most of the diesel consumption is seen in big trucks but nowadays diesel is also used in other segment vehicles. Diesel is 33% more efficient than gasoline when it comes to fuel mileage. This means that if we get 40 miles to the gallon on gasoline, a diesel equivalent engine will give 53.2 miles per gallon. A Diesel engine offers more torque than gasoline engines, this torque allows greater acceleration and helps to increase the fuel economy.
Factors which determine fuel efficiency:
- Environmental effects: This is the most primary reason why we choose the most efficient fuel. That is why we choose a diesel car as it uses less fuel per mile and it gives out less carbon dioxide. But diesel fuels are not totally pollution free. It releases some compounds which are carcinogenic and very harmful to the environment.
- Engine performance: Engine performance decides the cost as well as the efficiency of the fuel. Diesel has a better engine performance, therefore, it is cheaper.
- Noise: This is also one of the important criteria. Diesel does not produce smoke or dust but gives a roaring noise.