Systems and methods for detecting the presence of a burner flame using flame rectification are shown and described. A conductive flame sensor is positioned to conduct electricity to a burner flame when the burner is lit. The flame provides a conductive path to the burner conductive body and when operatively connected to an alternating current source, half-wave rectifies the current flowing to the sensor. A flame sensing circuit provides an output signal that is conditioned for use as an input to a flame indicator and/or a controller that is configured to shut off gas flow to the burner when no flame is present after an attempt at igniting the burner.

Methods and apparatus to thermally destruct volatile organic compounds are disclosed. An example thermal oxidizer for a furnace includes: an oxidation chamber comprising an inlet configured to receive exhaust gases from a furnace and an outlet configured to output resultant gases; and a plurality of heating elements within the oxidation chamber configured to heat the exhaust gases to oxidize one or more components of the exhaust gases between the inlet and the outlet to result in the resultant gases, the plurality of heating elements comprising resistive heating elements forming coils having respective axes, the plurality of heating elements being oriented within the oxidation chamber such that the axes of the coils are transverse to an exhaust gas flow direction from the inlet to the outlet of the oxidation chamber.

A method is provided for operating a fuel-operated vehicle heater (10) during a start phase of combustion operation. The heater includes a combustion air feed device (26) feeding air and a fuel feed device (22) feeding fuel (B) to a burner area (12) with a combustion chamber (16). An electrically energizable ignition element (32) ignites a fuel/air mixture formed. The method includes energizing the ignition element (32) in a preheating phase prior to the fuel feed, at a time of entry into an ignition phase, detecting electrical resistance of the ignition element (32) and determining a desired resistance based on the electrical resistance of the ignition element (32) detected and operating the ignition element (32) in a resistance-regulating operating mode during the ignition phase such that an actual resistance of the ignition element (32) is in the range of the determined desired resistance of the ignition element (32).

A combustion system such as a furnace or boiler includes a perforated reaction holder configured to hold a combustion reaction that produces very low oxides of nitrogen (NOx).

Methods and apparatus to thermally destruct volatile organic compounds are disclosed. An example thermal oxidizer for a furnace includes: an oxidation chamber comprising an inlet configured to receive exhaust gases from a furnace and an outlet configured to output resultant gases; and a plurality of heating elements within the oxidation chamber configured to heat the exhaust gases to oxidize one or more components of the exhaust gases between the inlet and the outlet to result in the resultant gases, the plurality of heating elements comprising resistive heating elements forming coils having respective axes, the plurality of heating elements being oriented within the oxidation chamber such that the axes of the coils are transverse to an exhaust gas flow direction from the inlet to the outlet of the oxidation chamber.

An exhaust detecting safety switch assembly for turning off an oil burner when a disruptive quantity of exhaust is detected includes an oil burner. The oil burner ignites oil to define a flame when the oil burner is turned on. An ignition is positioned in and is in electrical communication with the oil burner. The ignition is actuated to ignite the oil. A shutoff is electrically coupled to the ignition and is actuated to turn the oil burner off when the shutoff no longer detects the flame. A safeguard unit is mounted on and is in fluid communication with the oil burner. The safeguard unit is electrically coupled to the ignition. The safeguard unit detects when the oil burner emits a disruptive quantity of opaque exhaust and when detected turns the oil burner off. The safeguard unit is positioned to inhibit access to the safeguard unit.

A method is provided for operating a fuel-operated vehicle heater (10) during a start phase of combustion operation. The heater includes a combustion air feed device (26) feeding air and a fuel feed device (22) feeding fuel (B) to a burner area (12) with a combustion chamber (16). An electrically energizable ignition element (32) ignites a fuel/air mixture formed. The method includes energizing the ignition element (32) in a preheating phase prior to the fuel feed, at a time of entry into an ignition phase, detecting electrical resistance of the ignition element (32) and determining a desired resistance based on the electrical resistance of the ignition element (32) detected and operating the ignition element (32) in a resistance-regulating operating mode during the ignition phase such that an actual resistance of the ignition element (32) is in the range of the determined desired resistance of the ignition element (32).