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French chemist Jean-Baptiste André Dumas (1800-1844).
Dumas' apparatus; note the aspirator at 8. Sourced from J. A. Dumas, Ann. der Chem. and Pharm. , 1841,  38 , 141.

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.

Austrian chemist and physician Fritz Pregl (1869-1930).

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.

Categories of combustion

Basic flame types

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] ).

Types of combustion systems with examples. Adapted from J. Warnatz, U. Maas, and R. W. Dibble, Combustion: Physical and Chemical Fundamentals, Modeling and Simulation, Experiments, Pollutant Formation , 3 rd Ed., Springer, Berlin (2001).
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
Schematic representation of (a) laminar flow and (b) turbulent flow.

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.

Bunsen burner flames with varying amounts of oxygen and constant amount of fuel. (1) air valve completely closed, (2) air valve slightly open, (3) air valve half open, (4) air valve completely open.

Stoichiometric combustion and calculations

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] ).

Examples of stoichiometric, fuel-rich, and fuel-lean systems.
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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Source:  OpenStax, Physical methods in chemistry and nano science. OpenStax CNX. May 05, 2015 Download for free at http://legacy.cnx.org/content/col10699/1.21
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