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In 1923, Fritz Pregl ( [link] ) received the Nobel Prize for inventing a micro-analysis method of combustion. This method required only 5 mg or less, which is 0.01% of the amount required in Lavoisier's apparatus.
Today, combustion analysis of an organic or organometallic compound only requires about 2 mg of sample. Although this method of analysis destroys the sample and is not as sensitive as other techniques, it is still considered a necessity for characterizing an organic compound.
There are several categories of combustion, which can be identified by their flame types ( [link] ). At some point in the combustion process, the fuel and oxidant must be mixed together. If these are mixed before being burned, the flame type is referred to as a premixed flame, and if they are mixed simultaneously with combustion, it is referred to as a nonpremixed flame. In addition, the flow of the flame can be categorized as either laminar (streamlined) or turbulent ( [link] ).
| Fuel/oxidizer mixing | Fluid motion | Examples |
|---|---|---|
| Premixed | Turbulent | Spark-ignited gasoline engine, low NO x stationary gas turbine |
| Premixed | Laminar | Flat flame, Bunsen flame (followed by a nonpremixed candle for Φ>1) |
| Nonpremixed | Turbulent | Pulverized coal combustion, aircraft turbine, diesel engine, H 2 /O 2 rocket motor |
| Nonpremixed | Laminar | Wood fire, radiant burners for heating, candle |
The amount of oxygen in the combustion system can alter the flow of the flame and the appearance. As illustrated in [link] , a flame with no oxygen tends to have a very turbulent flow, while a flame with an excess of oxygen tends to have a laminar flow.
A combustion system is referred to as stoichiometric when all of the fuel and oxidizer are consumed and only carbon dioxide and water are formed. On the other hand, a fuel-rich system has an excess of fuel, and a fuel-lean system has an excess of oxygen ( [link] ).
| Combustion type | Reaction example |
|---|---|
| Stoichiometric | 2H 2 + O 2 -->2H 2 O |
| Fuel-rich (H 2 left over) | 3H 2 + O 2 -->2H 2 O + H 2 |
| Fuel-lean (O 2 left over) | CH 4 + 3O 2 -->2H 2 O + CO 2 + O 2 |
If the reaction of a stoichiometric mixture is written to describe the reaction of exactly 1 mol of fuel (H 2 in this case), then the mole fraction of the fuel content can be easily calculated as follows, where ν denotes the mole number of O 2 in the combustion reaction equation for a complete reaction to H 2 O and CO 2 , [link] .
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