Plasma-assisted combustion in a miniature microwave plasma torch applicator

Summary form only given. A compact microwave plasma torch has been designed and experimentally evaluated for operation in both plasma-only and plasma-assisted combustion modes. The torch is designed to be light and to operate at atmospheric pressure with a torch discharge size of less than 0.5 mm in diameter. The potential applications of the torch are materials synthesis, material cutting and welding, and various surface treatments. The operation of the torch in a combustion mode with hydrocarbon gases burning with oxygen is investigated with microwave power applied to modify the combustion process. The objective of this investigation is to quantify the changes in the combustion process as microwave power is applied to create or intensify the discharge. This torch employs an open-ended coaxial structure with the discharge located at the 12 mm outer diameter tip of the 5 mm diameter center conductor. Microwave power at 2.45 GHz is coupled into the torch applicator at power levels of 10-100 watts. The discharge is formed at atmospheric pressure where the feed gas flows through a nozzle hole of 200-500 mum diameter located at the end of the center conductor. The torch is experimentally evaluated with a variety of feed gas mixtures including argon, mixtures of argon with hydrogen, argon with nitrogen, methane and oxygen, and selected other hydrocarbon gases mixed with oxygen. This torch maintains discharges over a wide range of flows from diffusion flow for gentle surface processing to high velocity flow approaching supersonic velocities. Diagnostic measurements performed include (1) gas temperature measured by optical emission spectroscopy, (2) discharge power densities (3) discharge volume and size, and (4) atomic radical species produced by the plasma-assisted combustion mode. These measurements are made versus absorbed microwave power, gas flow rate, and gas mixture composition