<p>Laminar burning speed calculation at high pressures is challenging because of unstable surface conditions at large diameters. It is therefore desired to take these measurements as small dimensions (i.e., during the discharge process) when the flame kernel is smooth and stable. Taking accurate measurements at these sizes is challenging because the kernel growth rate does not only depend on the chemical reaction but also on other terms such as energy discharge, as well as radiative and conductive energy losses. None of these terms has been adequately assessed, due to the generation of ionized gas (i.e., plasma). In order to better understand these terms, in this work spark ignition in air under different pressures is investigated. Understanding the ignition event and modeling its behavior is important to capture accurate combustion measurements at pressures pertinent to the advanced high-pressure engines and technologies. The relationship between the electrical energy supplied to the spark and the thermal energy dissipated within a gas mixture has been studied. This work looks to relate the electrical discharge power to the volume of the ignition kernel measured via schlieren imagery.</p><p>In order to capture the data, a high-speed phantom camera and a custom schlieren setup are used to visualize the heated region of the plasma kernel. Voltage and current are captured using a DAQ system which are then used as the input to a thermodynamic model which is used to predict the volume vs time data of the spark event. The plasma studied in this work occurs for a duration of approximately 750 μs and has three distinct stages. First is the breakdown stage which occurs for about 20 ns. The second stage is a glow discharge in which the breakdown plasma grows and gains mass. This stage occurs for 50 to 100 μs. After the plasma grows to its maximum size the mass gain stops and the heated gas kernel continues to grow beyond the reach of the plasma region for the rest of the discharge. The model, which utilizes measured electrical power, thermodynamic properties of ionized air, and radiation losses of air show good agreement with the experimental kernel measurements. With these results we can conclude that the thermal data presented in this work sufficiently considers the major plasma and electrical losses in order to provide accurate model results. Further work will be done to show the effectiveness of the model in combustible media. Additionally, work can be done to describe the plasma kinetics involving the kernel growth immediately following the breakdown to increase agreement within this time range.</p>

Modeling Discharge Spark Ignition Using Zero Dimension Thermodynamic Model and Experimental Power Measurements at Various Pressures

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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