Patent Application
20110113762
This disclosure relates to the optimization of the reaction in a catalytic converter. More particularly, this disclosure relates to the use of powder-coated nickel foam as a resistor to increase the temperature of a catalytic converter device and thereby increase the efficiency of the device.
The temperature of a catalytic converter is one of the most significant factors which affects its efficiency. The efficiency drops off rapidly at both high and low temperatures, leaving a relatively narrow band of operating temperatures within which efficiency is highest. Most importantly, when automobile and truck engines begin operation, the catalytic converter is at a temperature too low to produce the reactions necessary to reduce the pollutants in the exhaust. When an engine first starts, the catalytic converter does almost nothing to reduce the pollution in the exhaust.
In the past, many catalytic converters have used the heat present in the vehicle exhaust stream to produce the temperatures necessary for the catalytic reactions to occur that transform harmful exhaust gases primarily carbon monoxide (CO) and nitric oxide (NO) into less harmful gases, primarily carbon dioxide, nitrogen (N2) and oxygen (O2) that are vented into the atmosphere. One solution used to heat the catalytic converter is moving the catalytic converter closer to the engine, allowing hotter exhaust gases to reach the converter. This positioning allows the catalytic converter to heat up faster, but may reduce the life of the converter by exposing it to extremely high temperatures.
Preheating the catalytic converter is another way to increase efficiency and reduce emissions. One of the most prevalent ways to preheat the converter is to use electric resistance heaters. The 12-volt electrical systems on most cars and trucks cannot provide enough energy or power to heat the catalytic converter fast enough. Hybrid cars with high-voltage battery packs can sometimes provide enough power to heat up the catalytic converter very quickly.
Catalytic converters in diesel engines are even less efficient than standard engines because diesel engines run cooler than standard engines. One solution to this problem is a system that injects a urea solution (an organic compound made of carbon, nitrogen, oxygen and hydrogen) in the exhaust pipe before it reaches the converter. The urea evaporates and mixes with the exhaust, creating a chemical reaction that reduces nitrogen oxides (NOx). The urea reacts with NOx to produce nitrogen and water vapor, reducing the nitrogen oxides in exhaust gases. Another method is heating a diesel particulate trap sufficiently to incinerate the soot formed in the trap as a result of the condensation of soluble organic fractions in the exhaust stream. This heating is accomplished thermally with exhaust gas.
This invention uses metallic foam as both a support for the catalyst(s) and as the resistor itself when attached to a closed-loop thermostatically-adjusted controller. This invention uses the residual electrical energy generated by the engine, much as in the manner of other electronic devices, such as the vehicle radio, to heat the catalytic converter directly to a more efficient temperature at which to conduct the catalytic reaction. The disclosed invention consists of a method of optimizing the temperature of diesel engine exhaust comprising: providing a substrate consisting of a metal foam; coating the substrate with a catalytic material; heating the substrate with electric current to a temperature range designed to optimize the catalytic reaction; and causing the diesel engine exhaust to flow over the substrate so that the catalytic material interacts with said exhaust. In all embodiments of the invention, the substrate may be in the form of nickel foam or metal foam. The catalytic material may also comprise a washcoat. The catalytic material may be comprised of various catalysts, including: an iron manganese catalyst; a titanium dioxide catalyst; a selective catalytic reduction (“SCR”) catalyst; or a platinum catalyst.
The disclosed invention also may consist of a diesel engine exhaust system comprising: a housing having an inlet for receiving diesel exhaust; a metallic foam substrate within the housing, the substrate having a catalytic coating; an electrical system for heating said substrate; and an outlet for emitting diesel exhaust. In all embodiments of the system, the substrate may be in the form of nickel foam or other metal foam. The catalytic coating may also comprise a washcoat. The catalytic coating may be comprised of various catalysts, including: an iron manganese catalyst; a titanium dioxide catalyst; an SCR catalyst; or a platinum catalyst.
A schematic for the claimed metallic foam substrate and resistor is shown in
The disclosed invention describes the use of a power-coated nickel foam as a resistor to increase the temperature of the catalytic converter device and thereby increase the efficiency of the device. Traditionally, a catalytic converter consists of several components: (1) the substrate, which is most often a ceramic honeycomb or stainless steel foil honeycomb; (2) the washcoat, which is often a mixture of silicon, aluminum and other elements and which forms a rough, irregular surface which has a far greater surface area than the substrate surface; and (3) the catalyst itself, which is often a precious metal such as platinum or palladium. The catalyst is added to the washcoat (in suspension) before application to the substrate.
In the disclosed method and apparatus, the substrate is a powder-coated nickel foam, which is manufactured in accordance with the process disclosed in German Patent DE1025006009164A1, dated Feb. 20, 2006, entitled “Diesel Particle Filter with open-pored metal foam” held by Inco Limited. The good ductility and high flexibility of the 100% open-pore material allows the substrate design to be determined freely. Different porosities make it possible to define the level of deep-bed filtration in the system. The foam acts as an effective substrate due to its high temperature and corrosion resistance, coupled with a very good soot storage capacity. During the manufacturing process, the nickel metal foam is coated and thermally treated with a high-alloy metal powder tailored to the particular application and design. Fusion occurs, enlarging the specific surface of the light metal foam. At the same time, the temperature resistance of the thermal conductive alloy foam increases up to 1,000° C. with peaks of up to 1,200° C. The foam is flexible, ductile, and can be cut at any length. The material may be sintered and manufactured as sheets. Other types of metallic resistance products are known in the art and may also be used in the disclosed method and apparatus.
A number of different wash coats and/or catalysts can be applied to the foam so that the foam can be used as a catalytic converter. The catalysts applied can increase the amount of nitrogen dioxide (NO2), decrease the amount of nitrogen oxides (NOX), reduce the presence of carbon monoxide (CO), and reduce the presence of hydrocarbons. Further, the foam can act as a DPF, which passively regenerates itself. As disclosed in German Patent DE102006009164A1, the powder coating applied to the nickel foam is a combination of iron and chromium. After the powders are applied, the material is sintered to form a material with a much larger surface area.
The powder-coated nickel foam has no catalytic properties itself but is an excellent support for catalytic material, including an appropriate wash coat and/or catalyst. At least four different catalytic coatings have been applied to the foam, including: (1) an iron manganese catalyst that converts CO to carbon dioxide (CO2); (2) a catalytic washcoat and platinum catalyst which convert CO to CO2, and hydrocarbons to CO2 and water vapor; (3) a catalyst made from titanium dioxide (TO2), which converts NO2 to nitric oxide (NO); and (4) a catalyst that converts NOx to nitrogen gas (N2) and water. The catalyst that converts NOx to nitrogen gas (N2) and water may be any type of SCR catalyst, including oxides of base metals (such as vanadium and tungsten) and zeolites. Other catalytic coatings may exist commercially or in the current art that can be applied to the nickel foam.
It is well-known that each catalytic material has a temperature where the catalyst is most effective. In many diesel systems, the exhaust emissions never or only slowly reach the temperature where the catalyst is most effective. In the disclosed invention, the metal foam, which is being used as the catalytic support, is imbued with electric current to control the catalyst at the most efficient temperature with a small amount of current. The current is generated as a by-product of engine activity, so it is unnecessary to introduce additional energy into the engine system. The system is a closed-loop system that uses a thermocouple to measure the temperature of the exhaust stream and then regulates the amount of current to maintain a preselected temperature. The circuitry for the system can be designed without undue experimentation by those skilled in the electronic arts.
The disclosed apparatus consists of an adjustable direct-current electricity source with the circuit attached either to a battery or generator source that can supply adequate current to increase the temperature of the metal foam. The current source is thermostatically-controlled by a proportionate controller that receives temperature input from a thermocouple or other type of temperature sensor, including but not limited to, resistance thermometers, filled-system thermometers, bimetal thermometers or radiation pyrometers. The system also includes a controller which can be constructed in accordance with devices described in Chapter XXII of the Chemical Engineer's Handbook. The current is conveyed by wires connected to buss bars connected to the opposite sides of a sheet or other form of the metallic foam. The foam is mounted in a container that receives the emissions from the engine, as is used typically to house the catalytic converter supports. In the disclosed invention, however, the catalytic converter support also acts as a heater to heat the catalyst and surrounding exhaust to optimal temperatures.
