High-temperature gas sensors

An acoustic wave (AW) sensor for sensing the amount of a gas in a fluid flow, comprising:

• a) a first gas-absorbing layer;
• b) a high-temperature-stable piezoelectric plate coupled to the first gas-absorbing layer, the high-temperature-stable piezoelectric plate including at least one material selected from the group consisting of AlN, GaN, Al1-xGaxN (0≦x≦1), GaPO4, AlPO4, and materials having the crystal structure of Ca2Ga2Ge4SiO14;
• and
• c) a controller coupled to the high-temperature-stable piezoelectric plate to measure a resonant frequency in the high temperature stable piezoelectric plate correlated with an amount of gas absorbed by the first gas absorbing layer,
• whereby the amount of a gas in a fluid flow is sensed.

A method of sensing the amount of NOx in an exhaust stream from an internal combustion engine, comprising:

• a) operating an acoustic wave (AW) sensor at a resonant frequency, the AW sensor having a La3Ga5SiO14 high temperature stable piezoelectric plate coupled to a barium carbonate layer;
• b) combining an exhaust stream including a NOx component with the barium carbonate layer at a temperature of at least about 500° C., thereby reacting at least a portion of the NOx component with the barium carbonate layer to form barium nitrate;
• c) sensing at least one resonant frequency of the high temperature stable piezoelectric plate;
• and
• d) correlating the resonant frequency with the amount of NOx reacted to form barium nitrate,
• thereby sensing the amount of NOx in the exhaust stream.

A method of reducing NOx to N2 in the exhaust stream of an internal combustion engine, comprising:

• a) directing an exhaust stream including a NOx component from an internal combustion engine to a NOx trap coupled in series with an acoustic wave (AW) NOx sensor, thereby reacting at least a portion of the NOx component with barium carbonate to form barium nitrate, wherein:
• i) the trap includes a second barium carbonate layer;
• and
• ii) the AW sensor, located downstream of the trap with respect to the flow direction of the exhaust stream, includes a La3Ga5SiO14 high temperature stable piezoelectric plate coupled to a first barium carbonate layer;
• b) sensing at least one resonant frequency of the high temperature stable piezoelectric plate;
• c) correlating the resonant frequency with the amount of NOx absorbed in the first barium carbonate layer, thereby sensing a saturated NOx trap condition and an unsaturated NOx trap condition;
• d) operating the engine in a lean burn mode upon sensing an unsaturated NOx trap condition, thereby reacting at least a portion of NOx resulting from the lean burn condition with the second barium carbonate layer to form barium nitrate;
• and
• e) operating the engine in a rich burn mode upon sensing a saturated NOx trap condition, thereby purging at least a portion of the barium carbonate layers of barium nitrate to release NOx, and reducing at least a portion of the released NOx to N2.

A method of sensing the amount of ammonia in an exhaust stream from an internal combustion engine, comprising:

• a) operating an acoustic wave (AW) sensor at a resonant frequency, the AW sensor having a La3Ga5SiO14 high temperature stable piezoelectric plate coupled to a zeolite gas absorbing layer, the zeolite having a nanopore size between about 0.5 nm and about 0.6 nm;
• b) combining an exhaust stream including an ammonia component with the zeolite gas absorbing layer at a temperature of at least about 500° C., thereby absorbing at least a portion of the ammonia into the zeolite gas absorbing layer;
• c) sensing at least one resonant frequency of the high temperature stable piezoelectric plate, and correlating the resonant frequency with the amount of ammonia absorbed in the zeolite gas absorbing layer;
• d) sensing the electrical complex impedance of the zeolite gas absorbing layer, and correlating the electrical complex impedance with the amount of ammonia absorbed in the zeolite gas absorbing layer, and
• e) comparing the amount of ammonia absorbed in the zeolite gas absorbing layer according to the frequency and the electrical complex impedance,
• thereby sensing the amount of ammonia in the exhaust stream.

An acoustic wave (AW) sensor for sensing the amount of a NOx component in an exhaust stream of an internal combustion engine, comprising:

• a) a first barium carbonate layer having a surface area to volume ratio of less than about 1×107 cm2:1cm3;
• b) a La3Ga5SiO14 high temperature stable piezoelectric plate coupled to the first barium carbonate layer;
• and
• c) a controller coupled to the La3Ga5SiO14 high temperature stable piezoelectric plate that correlates a resonant frequency in the high temperature stable piezoelectric plate with an amount of NOx absorbed by the first barium carbonate layer,
• whereby the amount of NOx in an exhaust stream of an internal combustion engine is sensed.

A system for reducing NOx to N2 in the exhaust stream of an internal combustion engine, comprising:

• a) an acoustic wave (AW) NOx sensor including a first barium carbonate layer having a surface area to volume ratio of less than about 1×107 cm2:1 cm3, and a La3Ga5SiO14 high temperature stable piezoelectric plate coupled to the first barium carbonate layer;
• b) a NOx trap coupled in series with the AW NOx sensor, the NOx trap including a second barium carbonate layer, the AW NOx sensor being located downstream of the NOx trap with respect to the flow direction of an exhaust stream from an internal combustion engine;
• and
• c) a controller that is:
• i) coupled to the La3Ga5SiO14 high temperature stable piezoelectric plate to sense a resonant frequency in the high temperature stable piezoelectric plate;
• and
• ii) in electronic communication with the internal combustion engine to direct the engine to operate in a lean burn mode and a rich burn mode,
• whereby at least a portion of NOx is reduced to N2 in the exhaust stream of the internal combustion engine.

An acoustic wave (AW) sensor for sensing the amount of an ammonia component in an exhaust stream of an internal combustion engine, comprising:

• a) a zeolite gas absorbing layer having a surface area to volume ratio of less than about 1×107 cm2:1 cm3, the zeolite having nanopore sizes between about 0.5 nm and about 0.6 nm;
• b) a La3Ga5SiO14 high temperature stable piezoelectric plate coupled to the zeolite gas absorbing layer;
• and
• c) a controller that is:
• i) coupled to measure at least one resonant frequency of the La3Ga5SiO14 high temperature stable piezoelectric plate that is correlated with an amount of ammonia absorbed by the zeolite gas absorbing layer;
• and
• ii) coupled to measure at least one electrical complex impedance of the zeolite gas absorbing layer that is correlated with the amount of ammonia absorbed by the zeolite gas absorbing layer,
• whereby the amount of an ammonia component in an exhaust stream of an internal combustion engine is sensed.

A method of sensing the amount of a gas component in a fluid flow, comprising the steps of:

• a) operating an acoustic wave (AW) sensor at a first resonant frequency, the AW sensor including a piezoelectric plate coupled to a first gas-absorbing layer, the gas absorbing layer comprising a metal carbonate;
• b) combining a fluid flow having a gas component with the first gas-absorbing layer;
• and
• c) sensing at least one resonant frequency of the AW sensor,
• whereby the resonant frequency can be correlated with the amount of gas absorbed in the first gas-absorbing layer, thereby sensing the amount of gas in the fluid flow.

An acoustic wave (AW) sensor for sensing the amount of a gas in a fluid flow, comprising:

• a) a first gas-absorbing layer comprising a metal carbonate;
• b) a piezoelectric plate coupled to the first gas-absorbing layer;
• and
• c) a controller coupled to the piezoelectric plate to measure a resonant frequency piezoelectric plate correlated with an amount of gas absorbed by the first gas absorbing layer,
• whereby the amount of a gas in a fluid flow is sensed.

A method of sensing the amount of a gas component in a fluid flow, comprising the steps of:

• a) operating an acoustic wave (AW) sensor at a first resonant frequency, the AW sensor including a piezoelectric plate coupled to a first gas-absorbing layer, the gas absorbing layer including a metal carbonate or a zeolite;
• b) combining a fluid flow having a gas component with the first gas-absorbing layer;
• c) sensing at least one resonant frequency of the AW sensor;
• and
• d) sensing at least one electrical complex impedance value of the gas-absorbing layer,
• whereby the resonant frequency can be correlated with the amount of gas absorbed in the first gas-absorbing layer, and the electrical complex impedance value of the gas-absorbing layer can be correlated with the amount of gas absorbed by the first gas absorbing layer, thereby sensing the amount of gas in the fluid flow.

An acoustic wave (AW) sensor for sensing the amount of a gas in a fluid flow, comprising:

• a) a first gas-absorbing layer including a metal carbonate or a zeolite;
• b) a piezoelectric plate coupled to the first gas-absorbing layer;
• c) a controller;
• i) coupled to the piezoelectric plate to measure a resonant frequency piezoelectric plate correlated with an amount of gas absorbed by the first gas absorbing layer;
• and
• ii) coupled to the gas absorbing layer to measure an electrical complex impedance value correlated with an amount of gas absorbed by the first gas absorbing layer,
• whereby the amount of a gas in a fluid flow is sensed.