oxidation can also occur in other types of apparatus e g stationary and mobile automobile or diesel engines the purpose of combustion in these devices however is to generate reliable power and not to reduce pollutant emissions burners used in oxidation equipment are typically fired by raw natural gas there are several types of burner designs used in the industry two important classes of burners are a premix burners and b nozzle burners premix burners burn by hydroxylation and are used for natural draft applications and for forced draft applications when controlled exhaust conditions are required several high velocity burners though not strictly premix burners produce temperatures and mixing similar to premix burners e g see perry in premix burners the rate of flame propagation must be exceeded to assure that ignition cannot travel back into the burner flow mixing devices can sometimes be used to stabilize the flame and prevent the flame from travelling into the burner nozzle mix burners mix air and gas at the burner tile the burner may be a standard forced draft register with the gas emitted from holes drilled in the end of a supply pipe while easy to build the large holes in these burners can cause gas mixing problems these burners frequently produce a luminous gas flame small diameter.