i've been seeing some hot flames... like halle berry ;)... so i thought i'd write something about it...
SynGas Burner Flame
Furnace Oil Burner Flame viewed through a filter
Wood Fired Boiler Furnace Flame
SynGas Flame with Excess Air
NuWay Furnace Oil Burner
SynGas Burner
burner
the function of a burner is to combust fuel with air at a defined ratio... this ratio is known as the air-to-fuel-ratio (afr)... burners regulate the fuel flow and air flow so that the set afr is maintained... also the internal arrangement of burner is designed so that fuel mixes with air and reacts vigorously...
flame
a flame is a mixture of hot gases hot enough to radiate energy in the form of visible light...
when fuel reacts with air... it releases energy... and this energy is absorbed by the combustion gases (flue gases)... and this increases their internal energy which in turns makes them very hot... (like halle berry...)... according to plank's law of black body radiation... the flame must be sufficiently hot so that it would radiate energy in the form of visible light... or else the intensity of the radiation around the visible light wavelengths will be so low that the flame would not be visible... this is true for even a candle... where wax combusts with air...
flame color
there are two factors that contribute to the flame color... one is the black body radiation and this can be modeled using plank's theory... the other factor is spectral emission of various compounds and elements contained in the flue gas... (try burning a piece of copper wire... you'll notice that the flame color changes)...
adiabatic flame temperature
this is a measure of the combustion capability of a fuel... because... it is important to know how to extract heat from a fuel... so the adiabatic flame temperature is an important parameter is combustion science...
the adiabatic flame temperature is temperature a fuel could produce with no heat or work transfer during sociometric combustion (complete combustion)... there are two types of adiabatic flame temperatures but we usually consider the constant volume adiabatic flame temperature as there is no work transfered as well...
the flame temperature of a fuel obviously depends on the air-to-fuel ratio... since oxygen in air is "diluted" with nitrogen... having excess air in a combustion reaction would cause the flame temperature to go down... by increasing the oxygen concentration by mixing oxygen to combustion air it is possible to generate high(er) temperature flames... like the cutting flame in gas welding... the flame temperature drops as it transfers heat by radiation and convection...
listed bellow are adiabatic flame temperatures of some fuels...
| Fuel | Formula | Adiabatic Flame Temp (°C) |
| Hydrogen | H2 | 2045 |
| Methane | CH4 | 1957 |
| Acetylene (with air) | C2H2 | 2400 |
| Acetylene (with O2) | C2H2 | 3100 |
| Diesel | 2138 | |
| Coal | 2211 | |
| SynGas / Producer Gas / Wood Gas / Town Gas | CO & H2 | 1100 |
excess air
the stoichiometric ratio is the minimum afr when complete combustion occurs...
a rich mixture is when there is more fuel and thus the afr of a rich mixture is lower (because there is less air and more fuel) than the stoichiometric aft... a lean mixture is the opposite of that... when there is more air than the stoichiometric ratio... so the afr is higher than the stoichiometric aft
most burners allow some amount of excess air in order to ensure complete combustion... for example... most diesel burners allow about 10-20% excess air... this has a negative effect because it causes the flame temperature to drop...