Design and Verification of a Speed of Sound Sensor for Biogas for Future use in a Fuel Flexible Burner
Due to strict emissions regulations, combustion systems in California are required to attain and maintain ultra-low emissions while achieving high efficiencies. Further, an increasing desire to utilize fuels that are derived from renewable sources to help mitigate emission of greenhouse gases is requiring more flexibility of these systems. As a result, combustion systems are adopting an increasing array of sensors and controls to achieve the desired performance.
The subject of this thesis is the development of a speed of sound (SOS) sensor for use in fuel flexible combustion systems. The goal is to facilitate the ability of the combustion system to self-tune to selected combustion characteristics, primarily the fuel stock. The fuel of primary interest is biogas, also known as digester gas, which is promoted by California’s energy policy as a renewable and carbon neutral fuel. In order to make such a system commercially available and help offset natural gas consumption with the underutilized fuel an inexpensive speed of sound sensor was developed to detect fuel compositions. The sensor was designed using acoustic attenuation models to select a suitable transducer for detection of the speed of sound. It was found that by detecting the speed of sound of a gas mixture up to two components from a gas mixture could be found. The model used to design the sensor was later verified by measuring the excitation of transmitting and receiving transducers in different digester gas mixtures. Utilizing this speed of sound sensor would help reach ultra-low NOX emissions while operating at lean conditions.