Franz A. Pertl

Electromagnetic design of a novel microwave internal combustion engine ignition source, the quarter wave coaxial cavity igniter

Abstract New ignition sources are needed to operate the next generation of lean high-efficiency internal combustion engines. A significant environmental and economic benefit could be obtained from these lean engines. Towards this goal, the quarter wave coaxial cavity resonator (QWCCR), igniter was examined. A brief overview of the QWCCRs history is presented, followed by an electromagnetic analysis of the resonator. Microwave and radio-frequency gas breakdown at atmospheric and higher conditions are reviewed briefly. The presented analysis focuses on geometric and material parameter relations compared with performance characteristics, such as resonator quality factor and developed tip electric field which initiates a single-electrode high-pressure microwave gas breakdown. Conductor surface losses, dielectric losses, and radiation losses of the device are considered in the analysis, for which parameters of a prototype QWCCR were chosen for construction and evaluation of a resonator. Improved designs allowed successful integration of a QWCCR into a Briggs and Stratton engine. Given the capability of precise control, high power, and high energy delivery, and the opportunity for further optimization, the QWCCR has the potential to deliver more energy per ignition than a conventional spark plug and thus should be considered for application as a lean ignition source.

Comparative testing of a novel microwave ignition source, the quarter wave coaxial cavity igniter:

The performance of a novel microwave ignition source was experimentally tested against a standard multi-spark ignition system. Comparison of the combustion and detonation performance was measured. The growth of combustion kernels and the discharge pattern of the igniters were recorded using high-speed video cameras for visual comparison. The results showed that the transition of deflagration to detonation transition was comparable between the two ignition systems. Significant improvement in ignition of lean mixtures of ethylene and ethane were observed for the microwave ignition system over the baseline multi-spark ignition and thus should be considered for application as a lean ignition source.

Momentum Analytical Model of a Circulation Controlled Vertical Axis Wind Turbine

A possible method for modeling a Circulation Controlled - Vertical Axis Wind Turbine (CC-VAWT) is a vortex model, based upon the circulation of a turbine blade. A vortex model works by continuously calculating the circulation strength and location of both free and blade vortices which are shed during rotation. The vortices’ circulation strength and location can then be used to compute a velocity at any point in or around the area of the wind turbine. This model can incorporate blade wake interactions, unsteady flow conditions, and finite aspect ratios. Blade vortex interactions can also be studied by this model to assist designers in the avoidance of adverse turbulent operational regions. Conventional vertical axis wind turbine power production is rated to produce power in an operating wind speed envelope. These turbines, unless designed specifically for low speed operation require rotational start-up assistance. The VAWT blade can be augmented to include circulation control capabilities. Circulation control can prolong the trailing edge separation and can be implemented by using blowing slots located adjacent to a rounded trailing edge surface; the rounded surface of the enhanced blade replaces the sharp trailing edge of a conventional airfoil. Blowing slots of the CC-VAWT blade are located on the top and bottom trailing edges and are site-controlled in multiple sections along the span of the blade. Improvements in the amount of power developed at lower speeds and the elimination or reduction of start-up assistance could be possible with a CC-VAWT. In order to design for a wider speed operating range that takes advantage of circulation control, an analytical model of a CC-VAWT would be helpful. The primary function of the model is to calculate the aerodynamic forces experienced by the CC-VAWT blade during various modes of operation, ultimately leading to performance predictions based on power generation. The model will also serve as a flow visualization tool to gain a better understanding of the effects of circulation control on the development and interactions of vortices within the wake region of the CC-VAWT. This paper will describe the development of a vortex analytical model of a CC-VAWT.Copyright

Pitch Stability Analysis of an Airfoil in Ground Effect

The effects of placing a slot through a two-dimensional Wortmann FX 63-137 airfoil in ground effect were examined using computational fluid dynamics. The geometric shape of the slot was varied in three different ways: the width of the slot (w/c = 0.02, 0.04, and 0.06), the angle of the slot with respect to the airfoils chord line (d = 20, 30, and 40), and the position ofthe slot along the chord line, (x/c = 0.15,0.20, and 0.25). In addition, the airfoil was tested at five different angles of attack: ―3, 0, 5, 10, and 15 deg. The commercially available software Gambit 2.3.16 was used to create the computational grids. FLUENT 6.2.16 with the renormalized group k-e turbulence model was then used to simulate the flow. Pitch stability of the slotted airfoil was examined and results indicated that increasing the angle of attack of the slotted airfoil while in ground effect had a reduced increase in lift when compared with the lift generated by the baseline Wortmann FX 63-137 airfoil. Results also showed that the slot could be used to reduce center-of-pressure movement along the chord of the airfoil for the range of angles of attack investigated, thus improving the overall pitch stability of the airfoil. The slot geometry that produced a minimal center-of-pressure fluctuation was located at 20% of the chord length from the leading edge with a width of 2% and an angle of 20 deg between the slot and a line normal to the chord line.

Performance Predictions of a Circulation Controlled-Vertical Axis Wind Turbine With Solidity Control

Conventional straight bladed vertical axis wind turbines are typically designed to produce maximum power at tip speed ratio, but power production can suffer when operating outside of the design range. These turbines, unless designed specifically for low speed operation, may require rotational startup assistance. Circulation control methods, such as using blowing slots on the trailing edge could be applied to a Vertical Axis Wind Turbine (VAWT) blade. Improvements to the amount of power developed at lower speeds and elimination or reduction of startup assistance could be possible with this lift augmentation. Selection of a beneficial rotor solidity and control over when to utilize the blowing slots for the CC-VAWT (Circulation Controlled-Vertical Axis Wind Turbine) appears to have a profound impact on overall performance. Preliminary performance predictions indicate that at a greater range of rotor solidities, the CC-VAWT can have overall performance levels that exceed a conventional VAWT. This paper describes the performance predictions and solidity selection of a circulation controlled vertical axis wind turbine that can operate at higher overall capture efficiencies than a conventional VAWT.Copyright

IGNITION ENERGY TESTING OF THE QUARTER WAVE COAXIAL CAVITY RESONATOR WITH AIR- LIQUEFIED-PETROLEUM-GAS MIXTURES

Significant environmental and economic benefit could be obtained from engines that utilize lean mixtures ignited with high energy sources. To help reach this goal, the quarter wave coaxial cavity resonator (QWCCR) igniter was examined as an ignition source. Evaluation consisted of comparative ignition tests with liquefied-petroleum-gas (LPG) air mixtures of varying composition. Combustion of these mixtures was contained in a closed steel vessel with a pre-combustion pressure near one atmosphere. The resonator igniter was fired in this vessel with a nominal 150 W microwave pulse of varying duration to determine ignition energy limits for various mixtures. Mixture compositions were determined by partial pressure measurement and the ideal gas law. Successful ignition was observed through a view port in a combustion chamber. Microwave pulse and reflected power was captured in real time with a high-speed digital storage oscilloscope. Ignition energies and power levels were calculated from these measurements. As a comparison, ignition experiments were also carried out with a standard non-resistive spark plug where gap voltage and current were recorded for energy calculations. Results show that ignitable mixtures around stoichiometric and slightly rich compositions are combustible with the QWCCR using similar levels of energy as the conventional spark plug, in the low milli-Joule range. Combustion energy for very lean mixtures could not be determined reliably for the QWCCR for this prototype test, but are expected to be lower than that for a conventional spark. Given the capability of high power, high energy delivery, and opportunity for optimization, the QWCCR has the potential to deliver more energy per unit time than a conventional spark plug and thus could be considered be as a lean ignition source.

Feasibility of Pulsed Microwave Plasma Ignition for Use in SI-Engines

Ignition of the fuel-air mixture through compression and spark ignition are the two basic methods for igniting combustion mixtures in modern internal combustion (IC) engines. A significant environmental and economic benefit could be obtained if spark ignited (SI) engines were to be made more efficient. Higher thermal efficiencies could be obtained through operation with leaner fuel-air mixtures and through operations at higher power densities and pressures. These types of mixtures are often more difficult to ignite with traditional spark plugs. In pursuit of better ignition sources, this paper investigates a microwave plasma alternative to the traditional spark plug. Additionally, measurements of a novel pulsed microwave induced plasma ignition concept are presented. Measurements at atmospheric pressures show promising results with respect to energy and plasma formation delay. With some refinement, it is possible to produce sufficiently energetic microwave discharges, in a short enough time frame to make them feasible for ignition of SI engines in an automotive setting. These results justify further investigation to quantify the advantages such an ignition source may have to offer.Copyright

An analysis of the CTHA's resonance currents and the resulting radiation shapes

The contrawound toroidal helical antenna (CTHA), a novel low-profile antenna, is a bifilar antenna with four terminal connections. The two filaments of the antenna can be thought of as a two-wire transmission line whose resonances are determined by the boundary conditions present at the ends of the line. The CTHA is then approximated by a circular array of vertical loops for certain resonance modes. This structural approximation is used in an analytical approach to estimate the general shape of the radiation pattern of the CTHA for these cases. The analytical results are compared with simulation. Relatively good agreement was found, validating the structural approximation for rough pattern estimations.

Machine-vision-based bar code scanning for long-range applications

Bar code labeling of products has become almost universal in most industries. However, in the steel industry, problems with high temperatures, harsh physical environments and the large sizes of the products and material handling equipment have slowed implementation of bar code based systems in the hot end of the mill. Typical laser-based bar code scanners have maximum scan distances of only 15 feet or so. Longer distance models have been developed which require the use of retro reflective paper labels, but the labels must be very large, are expensive, and cannot stand the heat and physical abuse of the steel mill environment. Furthermore, it is often difficult to accurately point a hand held scanner at targets in bright sunlight or at long distances. An automated product tag reading system based on CCD cameras and computer image processing has been developed by West Virginia University, and demonstrated at the Weirton Steel Corporation. The system performs both the pointing and reading functions. A video camera is mounted on a pan/tilt head, and connected to a personal computer through a frame grabber board. The computer analyzes the images, and can identify product ID tags in a wide-angle scene. It controls the camera to point at each tag and zoom for a closeup picture. The closeups are analyzed and the program need both a barcode and the corresponding alphanumeric code on the tag. This paper describes the camera pointing and bar-code reading functions of the algorithm. A companion paper describes the OCR functions.

Design of a compact quarter wave coaxial cavity resonator for plasma ignition applications

Atmospheric and higher pressure RF and microwave plasma sources have numerous applications including material processing and spectroscopy. More recently, advantages in using such discharges for combustion ignition are being investigated. A particularly simple and compact microwave discharge generating device is the quarter wave coaxial cavity resonator (QWCCR). This paper presents a new, compacted design of such a device. A simple approximate analysis of the quality factor, Q, which is a measure of the resonant electromagnetic potential step-up capability is given, and compared to experimentally measured quality factors showing reasonable agreement. Analytic results indicate that the foreshortened folded cavity quality factors are comparable to tapered coaxial cavity designs.