Underfiring

The designer believes that by this combination of a combustion-chamber with the underfiring grate the combustion of the fuel is improved.

Underfiring of steam boilers, though not approved in this country, is very largely practised in America, […]

The lowered demand for coke during the depression, the necessity of maintaining the gas output and the ready availability of liquefied petroleum gas for underfiring led to the conversion of the North Shore coke plant of Becker ovens at Waukegan, Illinois, to this fuel. […] The thermal efficiency of the underfiring was about five per cent lower and somewhat more attention was required to keep the ovens in balance.

One of the major factors contributing to high particulate emissions from domestic burners is on-off cycling. […] Modulation and underfiring have been suggested as methods of reducing the significance of the startup transient. […] Underfiring consists of using a smaller (undersized) unit which has to stay on longer and, therefore, cycles less.

A steam temperature transient correction is a signal that is applied to the normal steam temperature control strategy to counter the impact of a transient process change. An example of a transient process change, and the most typical, would be overfiring or underfiring. Overfiring and underfiring are considered transients because they are not required to maintain a steady-state condition.

In natural gas-fired boilers, gas pressure is critical to proper burner operation and efficient combustion. Variations in gas pressure may cause over- or underfiring of the boiler. […] Underfiring may cause flame instability and poor combustion efficiency due to high levels of excess air.

Gas-burner maintenance should include these measures: […] Adjust gas input if combustion testing indicates overfiring or underfiring.

Damaged or clogged oil piping between the tank and the furnace will result in reduced fuel flow to the burner. This can cause burner underfiring, which is identified by: / Reduced heating capacity / High oxygen readings during combustion test / Low stack or flue temperature / Low temperature rise (temperature differential) across the heat exchanger […]