Inductor devices – With outer casing or housing – Potted type
Reexamination Certificate
2000-09-11
2003-03-18
Mai, Anh (Department: 2832)
Inductor devices
With outer casing or housing
Potted type
C336S090000, C336S092000
Reexamination Certificate
active
06535096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field Of The Invention
This invention relates to spark ignition systems for gas turbine and diesel engines that operate on diesel, natural gas or alternative fuels and require at least an initial ignition source.
2. Description Of The Prior Art
Current gas turbine engines for power production such as those used for hybrid electric vehicles and power generation require very high energy spark ignition systems due to use of low volatility fuels that are difficult to ignite. Typical high energy ignition systems are those used in the avionic industry for auxiliary power units (APUs). Some of these systems have severe emission control requirements that can be met only by providing very high energy ignition sources in order to start the engine before too much unburned fuel is released through the exhaust system. Diesel engines require glo-plugs to initiate combustion. In this case the glo-plug tip is heated to temperatures of >2000 F. which typically takes large amounts of current (~8 amps per plug) and lengthy warm up times.
To achieve the spark ignition performance needed for ignition and, at the same time, reduce the incidence of spark plug soot fouling, the spark ignition transformer core material must possess certain properties. Such core material must have moderately high magnetic permeability, must not magnetically saturate during operation, and must have low magnetic losses. The combination of these required properties severely curtails the availability of suitable core materials. Possible candidates for the core material include silicon steel, ferrite, and iron-based amorphous metal. Conventional silicon steel routinely used in utility transformer cores is inexpensive, but its magnetic losses are too high. Thinner gauge silicon steel with lower magnetic losses is too costly. Ferrites are inexpensive, but their saturation inductions are normally less than 0.5 T and Curie temperatures at which the core's magnetic induction becomes close to zero are near 200° C. This temperature is too low because a spark ignition transformer's upper operating temperature is typically about 180° C. Conventional iron-based amorphous metal has low magnetic loss and high saturation induction exceeding 1.5 T, however it shows relatively high permeability, limiting its energy storage capability.
Conventional avionic ignition systems can deposit very high energies (500 millijoules) into the spark, but typically operate at 10 Hz or less due to power consumption issues and also require DC-DC converters. They also have high rates of ignitor erosion, limiting the total duration of operation between ignitor changes and precluding their being operated continuously.
SUMMARY OF THE INVENTION
The present invention provides an ignition system containing a magnetic core-coil assembly and associated driver electronics. The system is capable of high pulse rate operation because of its rapid charge time (for example, ~100 microseconds using a 12 volt source), rapid voltage rise (for example, 200-500 nanoseconds), and rapid discharge time (for example, ~150 microseconds). It has low output impedance (30-100 ohms), produces high (>25 kV) open circuit voltages, and delivers high peak current through the spark (0.4-1.5 ampere) and high spark energy, typically 6-12 millijoules per pulse. Operation from a 12 volt battery source is readily accomplished using simple driver electronics at rates ranging from single shot to about 4 kHz, which are considerably greater than the current ignition systems can offer. The core-coil assembly may actually be operated using any voltage >5 volts to supply the driver electronics input voltage. The upper voltage supply limit is dependent on the voltage rating of the components used within the driver electronics, so the present system may be operated with conventional 12 V power or with readily available components at higher supply voltages including the 40-50 Volt system now being contemplated within the automotive industry. The charging time of the core-coil assembly is related to the supply voltage of the driver electronics. The higher the supply voltage, the faster the current will increase through the primary winding of the core-coil. This is due to loss reduction in the components that comprise the driver electronics and the ability to source more current. At lower voltages, the voltage drop across the switching element of the driver electronics (typically an IGBT) will limit the available voltage drop across the core-coil. This has the effect of increasing the charge time until a pre-determined current is flowing through the core-coil primary. This type of electronic system (electronic driver plus core-coil) output delivered through a surface gap plug (typical of avionic spark ignition systems) or a conventional J gap spark plug or derivatives results in a high power ignition source with localized heating capability. A “spark plug” or alternative term “ignitor” refers to a device that requires high voltage to create a spark across a gap. That gap can be a ceramic which is typical of a surface gap ignitor, or it can be an air gap, which is typical of a “J” gap spark plug. A “J” gap derivative refers to any other type of spark plug where an arc must be created over a distance similar to the distance between electrodes of a conventional “J” gap spark plug.
The magnetic core-coil assembly and ignition system of the invention may be operated at much higher pulse rates than prior art systems. The high pulse rates have a number of advantages applicable both to turbine and to diesel engines. Avionic systems are capable of high energy per spark but typically achieve only a 10 Hz rate. In the case of turbine engines fuel is burned substantially continuously. During engine start-up an ignition source must be provided. This source may advantageously employ an ignition system with a very high pulse rate, such as the 4 kHz or more that the present system can provide. The system is generally operated asynchronously, that is, spark activation is not synchronized to the position of other moving parts in the engine. After the engine is running continuously, the ignition system may be turned off, since the fuel burning is normally self-sustaining. However, in applications such as aerospace, safety considerations may dictate that the ignition system be activated at least periodically to insure the engine continues to run despite adverse conditions. For example, the intake of moisture into an aircraft turbine propulsion engine can cause a flameout, that is the quenching of the self-sustaining reaction, necessitating an engine re-start. For example, a gas turbine engine may flame out when an aircraft flies through rain. To avoid this, the ignition system may periodically be activated during known adverse conditions. However, the high Coulombic transfer of energy in a conventional system results in very rapid erosion of spark ignitors, thereby limiting the duty cycle and extent of the periodic activation of the system. In contrast, the present system experiences substantially slower rates of ignitor degradation, so the extra ignition can be used much more liberally, enhancing flight safety without the risk of ignitor failure.
The high pulse rate arc obtainable with the present system can also act as a localized heating source that can be activated essentially instantaneously, thus representing a cost effective replacement for glo-plugs in some applications such as diesel engines. The high pulse (>300 pulses per second) rate arc can create a greater heating of the fuel droplets or gas since the amount of total energy in the multiple arcs can exceed that of a conventional ignition system which is limited to approximately 110 pulses per second. In a diesel automotive or truck vehicle application, the engine may thus be started essentially on demand without the waiting time for a glo-plug to heat. In addition, a smaller battery may be used, since the total energy required for glo-plug heat up is much greater than the present system uses in start-up.
Gener
Fish Gordon E.
Grimes Donald Allen
Papanestor Paul A.
Rapoport William R.
VanBuskirk Bruce
Criss Roger H.
Mai Anh
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