2014 IR&D Annual Report

Microwave Methods for Enhanced Combustion in Natural Gas Engine Applications, 10-R8408

Principal Investigators
E. Sterling Kinkler Jr.
Christopher Chadwell
Barrett W. Mangold
Russell K. Barker

Inclusive Dates: 07/01/13 – 01/01/15

Background — Internal combustion engines (ICE) are used to convert energy stored in fossil fuels to usable power for transporting people and accomplishing work in an astonishing array of applications and industries. Planes, trains, and automobiles have been the most visible platforms using ICE technologies since the early 1900s, and the energy crises of the 1970s initiated much interest in higher fuel efficiencies. Accompanying the vast growth of operating ICE products, environmental issues are also major concerns. Current and especially future, economic, regulatory, and social pressures are fueling significant research in cleaner, higher efficiency combustion processes. Exhaust gas recirculation (EGR) techniques are frequently found in modern gasoline engines to help reduce harmful emissions and improve efficiency. High levels of EGR dilution can result in slower combustion and related ICE performance problems. Enhanced combustion of gaseous fuels has long been observed when electric fields are applied. Microwave (MW) techniques can produce very high intensity electric fields within an enclosed volume and are often used to develop intense electric fields that accelerate sub-atomic particles to near-speed-of-light velocities for modern physics research. International regulations allocate multiple MW frequency bands for use in industrial applications. Previous work at SwRI coupling MW power into an existing spherical chamber during combustion of gasoline/air mixtures has produced promising experimental results.

Approach — We sought to effectively couple MW power into an enclosed metallic chamber emulating the combustion chamber (CC) of modern ICE products. Design and test of fundamental methods and techniques to develop intense electric fields within a modern ICE CC is an enabling step toward implementation of running ICE platforms that can facilitate performance testing with MW enhanced combustion (MEC) techniques applied. Our approach was to research, fabricate, and test experimental MW coupling methods that can achieve significant MW fields within a CC and accommodate the many constraints imposed by the design and operation of modern commercial ICE products. The ICE CC is generally in the shape of a cylinder with variable height and contains a harsh internal environment, including cyclic high temperatures and pressures. Our research goals included implementation of high intensity internal electric fields for a range of ICE products and operating conditions. The large-bore natural gas ICE class was chosen due to physical and dimensional characteristics and the potential for relatively significant economic and environmental impact of improvements in efficiency and emissions, as engines in this class typically run 24/7 at high loads.

Accomplishments — The team performed research and preliminary design and analysis for a number of experimental MEC implementation methods and selected an initial design using a coaxial MW delivery system coupled to a small circular dielectric-filled MW waveguide. The filled waveguide was intended to couple and excite a desired MW field structure within the CC, maintain the necessary pressure envelope of the CC, and facilitate future MEC integration within commercial ICE products. The team completed design and fabrication of a filled waveguide, including features needed to efficiently transition between a coaxial MW feed and the waveguide. The team also completed design and fabrication of the laboratory CC fixture that mimics selected commercial CC shapes and sizes, and can facilitate MW system function, performance, and sensitivity experiments. The coaxial-fed filled waveguide and CC fixture have been combined, and system test and refinement completed. An agreement with a major engine manufacturer was concluded, providing the team with design information for current ICE products. Teaming with a large original equipment manufacturer provided realistic constraints on the design of the MEC system to accelerate acceptance of MEC technology in the large bore natural gas engine industry.

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.