# Staged combustion

Staged combustion is a method for reducing nitrogen oxides (NOx) emissions from combustion. There are two methods - air staged supply and fuel staged supply. Applications include boilers [1] and rocket engines.[2]

## Air staged supply

Characteristics
• NOX reduction rate from 50-75% is possible.
• Spatial separation of primary and secondary air.
• Control of combustion performance with primary air (sub-stoichiometric conditions, ${\displaystyle \lambda }$ < 1).
• Secondary air supply for burnout (usually,above stoichiometric conditions, ${\displaystyle \lambda }$>1 ).
• Simple configuration.
• Application at small scale combustions.

## Fuel staged supply

Characteristics
• NOX reduction rate from 50-75% is possible.
• Minor temperature instabilities at the reduction zone.
• Lower temperature necessary.
• Complex constructive configuration.
• Application at large scale combustions.

## History

Staged combustion dates back to the hot bulb engine of the 1890s. The first stage of combustion occurred inside the hot bulb and the hot gases were then forced out into the cylinder, where they mixed with additional air, and the second stage of combustion took place. At this time, staged combustion was used because it was a convenient method of ignition and it is unlikely that there would have been much concern about air pollution. A modern application of the principle is the Stratified charge engine, in which a rich mixture is ignited by a spark and the resulting flame-front ignites the weaker mixture elsewhere in the cylinder.