Combustion chamber includes a primary stage fuel burner to supply fuel into a primary combustion zone and secondary stage fuel burner supplies fuel into a secondary combustion zone. A sensor is positioned downstream from combustion chamber measuring concentration of one or more compounds. The sensor sends measurements of the concentration of compounds to a processor. The processor compares the measured concentration of the compound with a first threshold value and a second threshold value. The processor supplies more fuel to the primary stage fuel burner if the measured concentration is higher than the first threshold value, supplies more fuel to the secondary stage fuel burner if the measured concentration is higher than the second threshold value, maintaining fuel supply to the primary and secondary stage fuel burners if the measured concentration is lower than the first threshold value and lower than the second threshold value.

A burner assembly includes a burner housing having a fuel inlet; a burner for emitting ignited fuel to a heat exchanger; and an igniter and flame sensor assembly mounted to the burner housing, the igniter and flame sensor assembly including an opening therein providing an air path from an exterior of the burner housing to an interior of the burner housing, the opening sized to provide a predetermined drop of carbon dioxide at an outlet of the heat exchanger.

A system for widely spaced wavelength tunable diode laser absorption spectroscopy includes at least a first and second tunable diode laser generating laser light at a first and second wavelength, wherein laser light of the first and second wavelengths cannot co-propagate efficiently on the same single-mode fiber. A first fiber may be configured to carry light in the first wavelength, and a second fiber configured to carry light in the second wavelength. A fiber bundle may be formed from the distal ends of the first and second fibers stripped of their respective coatings, and arranged with their claddings adjacent to each other. One or more pitch heads are configured to project respective beams of laser light from the fiber bundle through a measurement zone. One or more catch heads located across the measurement zone receive the respective beams and direct the respective beams onto at least one sensor.

A gas analysis device includes: a measurement part configured to measure an absorption amount of a laser light including an absorption wavelength corresponding to at least two electronic level transitions having the same component contained in the combustion gas, by emitting the laser light on a plurality of measurement paths disposed to pass through the combustion gas; a standard setting part configured to set a standard gas concentration distribution and a standard temperature distribution on the basis of a measurement result of the measurement part; and an analysis part configured to obtain the gas concentration distribution and the temperature distribution by solving a function including the gas concentration distribution and the temperature distribution as variables so as to minimize a difference between the absorption amount measured by the measurement part and a standard absorption amount obtained on the basis of the standard gas concentration distribution and the standard temperature distribution.

A method for operating a furnace includes: providing a furnace comprising feed materials, an oxygen-containing stream, and a fuel-containing stream; providing a virtual sensor including a model generated using inputs including condition data collected by a physical gas sensor previously arranged in the furnace; placing the virtual sensor in communication with the furnace; operating the furnace by a combustion reaction, where during operation of the furnace: the virtual sensor receives the further condition data; in response to receiving the further condition data, the virtual sensor, using the model, determines the combustion product based on the further condition data; and based on the determined combustion product, the virtual sensor sends a signal to the furnace to automatically adjust a flow rate of at least one input.

Systems and methods for controlling a variable speed blower of a gas-fired heater associated with a swimming pool or spa are provided. A gas heater may include an air-fuel mixture chamber and a circuit. The circuit may be configured to receive a signal to initiate heating water and output a first control signal that operates a variable speed blower associated with the gas heater at a first rate of speed for a first time duration during ignition of the gas heater. The variable speed blower draws air into the air-fuel mixture chamber where the air is combined with gas fuel to ignite the air and the gas fuel to heat the water. The circuit may also be configured to output a second control signal that operates the variable speed blower at a second rate of speed after the first time duration has expired and after the gas heater is ignited.

Measuring a concentration of at least one target species is described. A first and second tunable diode laser are configured to generate laser light at a respective wavelength different from one another. A pitch head comprising a transmitting optic is optically coupled to the first and second tunable diode lasers via distal ends of the first and second optical fibers, and is oriented to project respective beams from each of the first and second distal ends through a measurement zone. A photodetector is configured to detect an optical power of light in the first and second wavelengths. A catch head located across the measurement zone from the pitch head is in optical communication with the pitch head to receive the respective beams from the first and second distal ends and direct the respective beams to the photodetector.

A residential gas heater assembly that comprises a gas heater, a blower assembly, a flue, and a combustion sensor assembly. The gas heater assembly comprises a burner chamber. The blower assembly comprises a housing. The blower assembly is adapted and configured to move air into the burner chamber and move combustion gases through the flue along a combustion gases flow path. The combustion sensor assembly is in fluid communication with a first location and a second location. The first location is within the combustion gases flow path. The gas heater assembly is adapted and configured such that operating the gas heater and the blower assembly induces a pressure differential between the first location and the second location to thereby cause a portion of the combustion gases to be drawn from the first location and flow to the combustion sensor assembly.