Abstract

The current method of achieving center chamber ignition in the Plasma Combustion Research Laboratory’s (PCRL) Constant Volume Combustion Chamber (CVCC) utilizes either a standard or modified spark plug. The standard spark plug achieves a representation of side wall ignition (similar to a combustion engine) while modified sparkplugs have an extended electrode to allow for a center camber ignition. Two of these modified spark plugs are placed on both sides of the chamber and can effectively seal and isolate the chamber from the electrode. However, the process of welding electrode material to the spark plug is time consuming and requires a large number of modified electrodes to effectively test multiple different spark gap sizes. Also, the process of cleaning the electrode after experimentation shortens the electrode over time with no method of compensation other than creating a new electrode. The new electrode design aims to reduce the structural weakness by removing the welded joint as well as allowing for linear adjustment between testing while remaining firm during testing. The new design presented utilizes high-temperature epoxy, ceramic and grafoil seals to make adjustments easy and precise. The design was analyzed, prior to building and testing, based on the stress induced from the sealant, the total rated voltage, the rated temperature, and the fracture stress of the ceramic material. The stress induced in the electrode device was analyzed with FEA and the results were found to be within the limits of the material in terms of the compressive and fracture strength. The maximum voltage was found to be around 30 kV. The design is tested with 3 different electrode sizes where the largest electrode of 1.3 mm (0.05 in) has the same diameter as the current experimental set up. Two smaller electrodes 1 mm and 0.5 mm (0.04 in and 0.02 in) are tested as well to show the range and capabilities of the new system. The voltage and current data of the new and old system are compared and are found to be statistically similar within a 90 percent confidence level. The new electrodes is also compared to the previous system in terms of electrical resistance, the peak power each system can provide to the plasma, the visual shape and duration of the plasma through high speed photography. The range of operation for a successful design includes pressures from 20 mTorr to 40 atm, temperatures up to 280 C, and voltages up to 25 kV.

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