Overfire

In the interest of smoke abatement, overfire jets are now installed on thousands of commercial and industrial coal-fired furnaces. [...] The overfire jet is a device for providing turbulence and/or overfire air above the fuel bed of hand-fired and stoker-fired furnaces.

Volatile matter in the vapor form and carbon monoxide just above the bed must be fully mixed with overfire air to complete the combustion process. At low firing rates it is important to minimize the amount of overfire air to prevent cooling of the volatile matter resulting in incomplete combustion and soot formation.

The primary flame zone can be operated fuel rich to reduce oxygen concentration, then additional air can be added downstream. This overfire air provides oxygen to complete combustion of unburned fuel and oxidizes carbon monoxide to carbon dioxide, creating a second combustion zone. Because there is so little fuel in this overfire zone, the peak flame temperature is low.

Over-fire boilers are the simplest and cheapest domestic boilers for burning wood logs. [...] In over-fire boilers, combustion takes place in the whole fuel batch more or less at the same time, as in wood-stoves. The boiler is normally equipped with a primary air inlet under the grate and a secondary air inlet over the fuel batch, into the gas combustion zone.

I found that the Chapelon steamed almost too freely, because on a strange locomotive and road one usually tends to overfire a little through a natural lack of confidence.

Overfiring the appliance may cause a house fire. If a unit or chimney connector glows, you are overfiring.

We have so far concentrated on creosote fires as a source of elevated flue gas temperatures. But overfiring the stove or fireplace – building a large, hot fire – can also produce very high temperatures.

BUBBLES IN GLAZE may be caused by too heavy an application, or by severe underfiring or overfiring. [...] LOSS OF COLOR IN CHINA PAINTING is a result of overfiring or mixing too much medium with the paint. Be careful not to overfire china colors, and if a light shade of a dark color is needed, apply the color very lightly rather than thinning too much.