Basics of combustion

Combustion takes place when gas, liquid, biomass or fossils react with oxygen in the air and create heat. The process requires three main elements, namely; fuel, oxygen and the source of ignition. Combustion can be likened to an explosion; however, this is a controlled explosion that takes place in a monitored space at a projected time.

“There are three “T’s” for combustion, they are; Temperature, Turbulence and Time” the late Dr Tony Biddlestone

Perfect combustion happens when the accurate quantities of the two main elements mix effectively. When fuel, in the form of gas, liquid or biomass has mixed with oxygen or another oxidant, ignition should follow. However, the mixing and burning of exactly the correct measurements of fuel and oxygen is only theoretical. Practically, fuels vary in chemistry, often minute by minute while the moisture and pressure of the air may also not be textbook, this makes it impossible to determine the perfect proportions needed in an actual combustion process.

The amount of heat above the ignition temperature must be efficient enough for impact. This mixture has to be given sufficient time for the burning process to be completed. Perfect combustion takes place when the three “T’s” have been closely followed. “To state that oxygen supports combustion is an understatement” said Riaan van der Walt during his presentation at the SADC Combustion Seminar that was hosted by SAGA on the 27th– 28th March 2018.

The burning flame after ignition

After ignition, the flame temperature varies, depending on the fuel. This flame may gradually increase, this will in turn create an increase on the electromagnetic radiation given off by the flame. The amount of oxygen the flame reaches determines the value of combustion achieved. Good combustion can be identified by minimal black-radiating soot. In turn, gas molecules are ionized and enough energy is generated.

The temperature of the flame varies vastly, for example, a candle flame sits at a temperature of only 1000 Degrees Celsius while a Dicyanoacetylene flame has 4990 Degrees Celsius, more than four times that of a candle flame.

Flames can be divided into two types, i.e. the Laboratory and the Industrial flame. The main difference between these two types of flames is that the information acquired from one may not necessarily be precisely the information acquired from the other. Lab conditions are superior to industrial conditions and the quantity of material being tested differs greatly, this will no doubt cause different conclusions. The complexity of the combustion process and what each type of flame communicates requires great skill and knowledge, this underlying factor was one of the main discussions amongst the delegates who attended the SADC Combustion Seminar.


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