TECHNIQUES FOR IMPROVING OPERATIONS OF MICRO-ELECTRO-MECHANICAL SYSTEMS (MEMS) CALORIMETERS (18-Jan-2010)

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TECHNIQUES FOR IMPROVING OPERATIONS OF MICRO-ELECTRO- MECHANICAL SYSTEMS (MEMS) CALORIMETERS

BRIEF ABSTRACT

    A method for improving the accuracy of a Micro-Electro-Mechanical Systems (MEMS) based calorimeter is disclosed. In general, MEMS based calorimeters are used to determine properties of materials, whereas here it is specifically used to determine the properties of gaseous fuels. A MEMS device (in a sensor) is coated with a catalyst and maintained at a constant temperature using a feedback control mechanism. A fuel-air mixture is passed across the MEMS device where combustion takes place in the presence of the catalyst. Measurement of the energy released by the fuel is obtained by monitoring the power that is required to maintain the constant temperature. A sensor detects the temperature changes in the catalyst. The varying and fixed catalyst temperature signals received from the sensor of the MEMS device are used to determine fuel constituent data.

KEYWORDS

Micro-Electro Mechanical System (MEMS), calorimeter, sensor, low heating value (LHV), Wobbe index, temperature, catalyst, gaseous fuel, fuel, air, gas chromatograph (GC), Infrared spectroscopy

DETAILED DESCRIPTION

    The variation of constituents in natural gas has been increasing as reserves from different parts of the world are utilized. Alternate gaseous fuels, which have large variations in their properties, are also being increasingly used. These variations place a demand on combustion systems to maintain high efficiency and avoid excessive emissions. For tackling such variations, there is a need for a sensor that measures the fuel constituents or properties online, allowing action to be taken by the combustion

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control system to deal with fuel constituent variation before such variation affects performance.

    A method of determining the properties of gaseous fuels using a MEMS based sensor is presented. The sensor consists of two MEMS heaters held at a constant temperature using a feedback control system. One of the devices is coated with an inert coating (referred to as 'reference device') while a second device is coated with a catalyst (referred to as 'active device'). The fuel air mixture is passed across the MEMS devices, and the power required to maintain a constant temperature on both the reference device and active device is monitored. The fuel air mixture will combust and energy will be released on the active device. The reference device, therefore, will require more power to be maintained at a constant temperature than the active device due to convective losses. The delta between the power required to maintain the active and reference devices at constant temperature provides a measure of the energy of the fuel.

    With catalytic combustion, it is not possible to completely combust all the fuel in the fuel air m...