{{Unreferenced, date=June 2011 Auto reignition is a process used in

gas burner A gas burner is a device that produces a controlled flame by mixing a fuel gas such as acetylene, natural gas, or propane with an oxidizer such as the ambient air or supplied oxygen, and allowing for ignition and combustion. The flame is gen ...

s to control ignition devices based on whether a burner flame is lit. This information can be used to stop an ignition device from sparking, which is no longer necessary after the flame is lit. It can also be used to start the sparking device again if the flame goes out while the burner is still supplying gas, for example, from a gust of wind or vibration.

Kitchen appliances

Most gas

ranges In the Hebrew Bible and in the Old Testament, the word ranges has two very different meanings. Leviticus In Leviticus 11:35, ranges probably means a cooking furnace for two or more pots, as the Hebrew word here is in the dual number; or perhaps ...

and cooktops use sparking devices to ignite the burner flame. This eliminates the need for a

pilot flame Merker Tankless water heating, tankless gas-fired water heater from the 1930s, with pilot light clearly visible through the aperture in the front cover. The large opening allowed for the manual lighting of the pilot light by a lit match or taper ...

, which wastes energy. Most of these sparking device-equipped ranges require the user to control the ignition sparking manually, resulting in a three-step process required to operate the burner: #turn burner knob to a position that opens the gas valve and activates the sparking (typically labelled "Light") #wait for ignition, typically 0.5 to 2 seconds #turn burner knob past lite position, to stop the sparking noise and burning out the ignition electrode, to a desired flame intensity One implementation of a gas burner with auto reignition senses the electrical conductivity of the flame. This nonzero

flame conductivity A flame (from Latin ''flamma'') is the visible, gaseous part of a fire. It is caused by a highly exothermic chemical reaction taking place in a thin zone. When flames are hot enough to have ionized gaseous components of sufficient density they ...

is because combustion of

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...

releases enough free electrons to support a small current in air. An electronic circuit then starts or stops the igniter from sparking, based on whether the flame is lit. This reduces the number of steps to turn a burner on from three to one: #turn knob to a desired flame intensity—while confirming flame ignites This is an elegant solution, compared to detecting flame via a

thermocouple A thermocouple, also known as a "thermoelectrical thermometer", is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the ...

, a

photoresistor A photoresistor (also known as a photocell, or light-dependent resistor, LDR, or photo-conductive cell) is a passive component that decreases resistance with respect to receiving luminosity (light) on the component's sensitive surface. The elect ...

or a mercury-filled sensor. No extra components or electrical connections between the sparker electrode and the spark module electronics are required. This convenience and safety feature is found only (as of June 2009) on higher priced gas ranges and cooktops.

The case for requiring auto reignition as a safety feature

Auto reignition lowers the risk of gas leaks: #if a flame goes out during operation, for example, from vibration or a gust of wind #due to misoperation—a user might not understand the "light" position must be maintained for about 0.5 to 2 seconds before turning the burner knob on fully. The user might, as a result, turn the burner knob on quickly past the "light" position without the burning actually igniting and leave the kitchen; thus leaving the gas burner leaking gas into the room. This feature is especially valuable on gas burners with several different short-term users, less likely to bother with or learn multi-step procedures—for example, gas ranges in rental properties, guest houses, or in office kitchens. Firelighting Cooking appliances