Ignition device for a gas appliance and method of operation
An ignition device for a gas appliance is provided. The ignition device includes a membrane and a plurality of heating elements embedded in the membrane, wherein the heating elements comprise a plurality of patterned resistors and wherein the plurality of heating elements are configured to heat a surface on application of voltage through the heating elements. The ignition device also includes a cavity disposed adjacent to the heating elements and configured to provide thermal isolation of the heating elements.
The invention relates generally to gas appliances, and more particularly to ignition devices for igniting a flow of gas in gas appliances and other gas-fired equipment. The invention may be applied to any application where ignition of a fuel air mixture is required.
Conventional gas appliances, such as those found in households, have one or more burners in which gas is mixed with air and burned at a cooktop or in an enclosed space, such as an oven. Various types of igniters are employed in such gas appliances for igniting the flow of gas. For example, in some systems spark igniters are employed that generate a spark to ignite the gas flowing to the burner. In certain other systems, ceramic hot surface igniters are employed that include heating elements for generating sufficient heat to ignite the gas supplied to the burner.
In certain systems, silicon carbide or silicon nitride hot surface igniters are employed for igniting the gas flow. Some of the problems with these conventional igniters are that they are porous, fragile, power hungry, relatively expensive and are fairly slow to reach ignition temperature. In addition, the resistance versus temperature characteristics of these conventional silicon carbide igniters may alter or drift over time, thereby adversely affecting their reliability.
Unfortunately, existing hot surface igniters need substantially high power for operation and can require an unacceptably long time to reach the required temperature for ignition. Further, heating elements of the igniters are exposed to the environment, resulting in accelerated failure of such elements due to degradation and contamination of the elements. Additionally, such igniters are often subjected to impacts from an operator during routine cleaning and maintenance, which may cause the igniter to break. Furthermore, such igniters require precise control of the voltage supplied to the heating elements. For example, a relatively high voltage may result in premature failure of the heating elements. Similarly, an applied voltage less than the required voltage may result in poor performance of the igniter.
Accordingly, it would be desirable to develop an ignition device for a gas appliance that has reduced power and voltage requirements. It would also be advantageous to develop an ignition device that requires relatively less time to reach the required ignition temperature, and is more robust and reliable.
BRIEF DESCRIPTIONBriefly, according to one embodiment an ignition device for a gas appliance is provided. The ignition device includes a membrane and a plurality of heating elements embedded in the membrane, wherein the heating elements comprise a plurality of patterned resistors and wherein the plurality of heating elements are configured to heat a surface on application of voltage to the heating elements. The ignition device also includes a cavity disposed adjacent to the heating elements and configured to provide thermal isolation of the heating elements.
In another embodiment, a gas appliance is provided. The gas appliance includes a cooktop and a gas burner assembly positioned in the cooktop and configured to receive a flow of gas. The gas appliance also includes an ignition device positioned adjacent to the gas burner assembly for igniting the flow of gas. The ignition device includes a two dimensional microplate including a membrane and a plurality of heating elements embedded in the membrane, wherein the heating elements comprise a plurality of patterned resistors and wherein the plurality of heating elements are configured to heat the microplate on application of voltage to the heating elements. The gas appliance also includes a cavity disposed adjacent to the heating elements and configured to provide thermal isolation of the heating elements.
In another embodiment, a method of igniting a flow of gas in a gas appliance is provided. The method includes receiving the flow of gas adjacent a microplate having heating elements embedded within a membrane and heating the microplate by applying a voltage to the heating elements embedded within the membrane. The method also includes igniting the flow of gas via the heated microplate.
DRAWINGSThese and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present technique function to provide an ignition device for gas range and cooktop applications. Although the present discussion focuses on ignition devices for a gas range, the ignition devices may be employed in other applications, such as gas heater devices, gas ovens, gas boils, gas kilns, and so forth. Turning now to the drawings and referring first to
In the illustrated embodiment, the gas range 10 includes four gas burner assemblies 20 positioned in the cooktop 14 and configured to receive a flow of gas for combustion. However, a greater or lesser number of the gas burner assemblies 20 may be envisaged. Further, each burner assembly 20 extends upwardly and a grate 22 is positioned over each burner assembly 20. In the present embodiment, each of the grates 22 includes a flat surface thereon for supporting the cooking utensils over the burner assembly 20. In the illustrated embodiment, an ignition device is disposed adjacent each burner assembly 20 and is configured to ignite the gas flow received by the gas burner assembly 20. The ignition device employed in the gas range 10 will be described in a greater detail below.
In the illustrated embodiment, the membrane 92 includes a non-electrically conductive high temperature material. Examples of the non-electrically conductive high temperature material include un-doped silicon carbide, silicon nitride, boron nitride or other suitable ceramic materials. Further, the heating elements 94 include a high temperature electrically conductive material that is compatible with the membrane 92. Examples of such materials include doped ceramics and metallic materials. In the illustrated embodiment, the heating elements 94 and contact pads 96 include doped silicon carbide. In other embodiments, the heating elements 94 may include other conductive high temperature materials such as platinum, titanium, doped polysilicon, or other metals. In certain embodiments, the membrane 92 may include a plurality of layers of doped and un-doped silicon carbide to provide a gradient of coefficient of thermal expansion for substantially reducing thermal stresses. In certain other embodiments, the membrane 92 may be coated with materials that will provide a gradation in thermal properties of the device 90. In operation, a voltage is applied to the heating elements 94 via the voltage source 84 (see
The ignition device 90 described above may be manufactured through a batch semiconductor fabrication process.
At step 132, a layer of electrically conductive material such as doped poly-silicon carbide is deposited on either sides of the silicon substrate 116 as represented by reference numerals 134 and 136. In this embodiment, the thickness of the doped poly-silicon carbide layers 134 and 136 is about 1 micrometers and the resistivity of the doped poly-silicon carbide is about 0.01 ohm-cm to about 0.2 ohm-cm. Further, at step 138, the doped poly silicon layer 134 on the front side of the substrate 116 is etched to create heating elements 140 and contact pads 142 on the substrate 116. As previously described, the heating elements 140 may be coupled to a power source for applying a voltage to the heating element 140 for heat generation. In the present embodiment, the doped poly-silicon carbide layer 134 is masked via a photoresist masking technique, and is subsequently etched via inductively coupled plasma (ICP) etching technique. However, other etching techniques may be employed.
At step 144, an electrically insulative material such as undoped poly-silicon carbide layers 146 and 148 are disposed on the doped poly-silicon carbide layers 140 and 136. In this embodiment, a thickness of the undoped poly-silicon carbide layers 146 and 148 is about 1 micrometers to about 5 micrometers and a resitivity of the layers 146 and 148 is about 2 ohm-cm to about 20 ohm-cm. Subsequently, at step 150, the undoped silicon layer 146 is etched to form contact pad hole 152. In this embodiment, the undoped silicon layer 146 is etched via photoresist masking and ICP etching techniques. Moreover, the silicon carbide layers 136 and 148 are dry etched on the backside as represented by step 154. A layer of silicon nitride 156 is deposited on the backside of the substrate 116 via plasma enhanced chemical vapor deposition (PECVD) technique, as represented by step 158 to serve as an etch mask for step 160. However, other materials such as silicon carbide may be employed as an etch mask. In certain embodiments, the nitride layer 156 may be deposited via low pressure chemical vapor deposition (LPCVD) technique. In certain embodiments, the nitride layer 156 may be deposited via low pressure chemical vapor deposition (LPCVD) technique.
Further, at step 160 the oxide layer 128 is patterned and etched to form patterned oxide 162 and 164 to expose the silicon for etching. In this embodiment, a cavity 166 is formed by wet etching, such as by employing potassium hydroxide (KOH). In certain other embodiments, the cavity 166 may be formed using Deep Reactive Ion Etching. Further, at step 168, the silicon nitride layer 156 and silicon dioxides 162 and 164 are removed by employing a combination of wet and dry etch techniques as represented by reference numeral 168. Moreover, a silicon wafer 170 is bonded in vacuum adjacent the cavity 166 as represented by step 172 to form the ignition device.
The various aspects of the structures and methods described hereinabove have utility in gas appliances and heating equipment, used in various applications. In particular, the ignition devices described above may be employed in gas fuel ignition applications, such as furnaces and cooking appliances, as well as in various industrial and commercial settings, such as on boilers, water heaters, industrial furnaces, and so forth. As noted above, the ignition device needs substantially less power for operation and attains the required ignition temperature within a relatively short period of time. Further, the reduction in power consumption allows for a continuous operation of the ignition device and provides the ability to maintain an energizing signal to the device while gas is flowing, so as to automatically reignite the flame if it is extinguished. Additionally, the heating elements of the ignition device are not directly exposed to the environment, thus resulting in a more robust device.
It should be noted that, as described and claimed herein, the invention offers improved structures and methods for gas appliances generally. That term is intended to be understood broadly to include both consumer appliances, as well as other gas-burning devices and systems of the types mentioned above.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Claims
1. An ignition device for a gas appliance, comprising:
- a membrane;
- a plurality of heating elements embedded in the membrane, wherein the heating elements comprise a plurality of patterned resistors and wherein the plurality of heating elements are configured to heat a surface on application of voltage to the heating elements; and
- a cavity disposed adjacent to the heating elements and configured to provide thermal isolation of the heating elements.
2. The ignition device of claim 1, wherein the membrane comprises a non-electrically conductive material.
3. The ignition device of claim 2, wherein the membrane comprises un-doped silicon carbide, or silicon nitride, or boron nitride.
4. The ignition device of claim 1, wherein the heating elements comprise an electrically conductive material.
5. The ignition device of claim 4, wherein the heating elements comprise doped silicon carbide.
6. The ignition device of claim 1, wherein the cavity is sealed in vacuum, or in an inert environment to substantially prevent degradation of the heating elements.
7. The ignition device of claim 1, wherein the membrane comprises contact pads configured to provide electrical connection for the ignition device.
8. The ignition device of claim 7, wherein the contact pads comprise doped silicon carbide, or doped silicon carbide coated with nickel, or gold, or platinum, or tungsten, or combinations thereof.
9. The ignition device of claim 1, wherein the ignition device is configured to sense a temperature based upon a measured resistivity of the heating elements.
10. The ignition device of claim 1, wherein the membrane comprises a plurality of layers of doped and un-doped silicon carbide to provide a gradient of coefficient of thermal expansion for substantially reducing thermal stresses.
11. The ignition device of claim 1, wherein the heating elements comprise a plurality of microwires sealed within the cavity in vacuum, or an inert environment and wherein the microwires comprise doped silicon, or tungsten, or molybdenum disilicide.
12. The ignition device of claim 11, further comprising an anti-oxidation layer disposed adjacent to either side of the membrane for substantially preventing the membrane from oxidation at high temperatures.
13. The ignition device of claim 1, further comprising mechanical stress relief structures to manage stress due to thermal expansion.
14. The ignition device of claim 1, wherein the heating elements are disposed at a pre-determined distance from the membrane.
15. A gas appliance, comprising:
- a gas burner assembly configured to receive a flow of gas; and
- an ignition device positioned adjacent to the gas burner assembly for igniting the flow of gas, wherein the ignition device comprises: a two dimensional microplate including a membrane; a plurality of heating elements embedded in the membrane, wherein the heating elements comprise a plurality of patterned resistors and wherein the plurality of heating elements are configured to heat the microplate on application of voltage to the heating elements; and a cavity disposed adjacent to the heating elements and configured to provide thermal isolation of the heating elements.
16. The gas appliance of claim 15, wherein the membrane comprises a non-electrically conductive material and the heating elements comprise an electrically conductive material.
17. The gas appliance of claim 15, wherein the cavity is sealed in vacuum, or in an inert environment to substantially prevent degradation of the heating elements by oxidation.
18. A method of igniting a flow of gas in a gas appliance, comprising
- receiving the flow of gas adjacent a microplate having heating elements embedded within a membrane;
- heating the microplate by applying a voltage to the heating elements embedded within the membrane; and
- igniting the flow of gas via the heated microplate.
19. The method of claim 18, wherein applying the voltage comprises applying the voltage to doped silicon carbide microscale resistors embedded within a un-doped silicon carbide membrane.
20. The method of claim 18, further comprising sensing the temperature of the microplate via measuring a resistivity of the microplate.
Type: Application
Filed: Dec 7, 2005
Publication Date: Jun 7, 2007
Inventors: Kanakasabapathi Subramanian (Clifton Park, NY), Richard Saia (Niskayuna, NY), Aaron Knobloch (Rexford, NY), Nicholas Okruch (Mt. Washington, KY), David Najewicz (Prospect, KY)
Application Number: 11/296,139
International Classification: F23Q 9/00 (20060101); F23Q 9/08 (20060101);