Auto reignition

Auto reignition is a process used in gas burners 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, for example from a gust of wind or vibration.

Kitchen appliances

Most gas ranges and cooktops use sparking devices to ignite the burner flame. This eliminates the need for a pilot flame, which wastes energy. Most of these sparking device-equipped ranges require the user to control the ignition sparking manually, resulting in a four-step process required to operate the burner:

#turn burner knob to a position that opens the gas valve and activates the sparking (typically labeled "Lite")
#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
#turn knob to a desired flame intensity (can be combined with step 3 with practice)

One implementation of a gas burner with auto reignition senses the electrical conductivity of the flame. This nonzero [http://www.durag.com/html/heg/heglit.html flame conductivity] is because combustion of natural gas 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 four 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 photoresistor 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 December 2006) 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 while the user is not present, for example from vibration or a gust of wind
#due to misoperation--a user might not understand the "lite" 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 fully, past the "lite" position, observe no flame, then give up and leave the room, thus leaving the gas burner leaking gas into that 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.

(original author does not know the history of auto reignition, or the full case for and against requiring it on kitchen gas appliances) (any fire accident reports where misunderstanding of manual ignition isolated as the cause?)