Electronic emissions control

A method of controlling emissions from an internal combustion engine including governing engine speed with respect to a constant speed, maintaining an air/fuel ratio of the engine, flowing exhaust from the engine through an exhaust system containing a catalyst, monitoring a variable with a feedback sensor located upstream of the catalyst, and controlling the air/fuel ratio of the engine as a function of the variable. In one application, the engine is configured for marine applications, including electric power generation and propulsion.

TECHNICAL FIELD

This invention relates to controlling emissions from internal combustion engines.

BACKGROUND

Reducing combustion engine exhaust emissions is a continual object of research and development, driven both by awareness of environmental effects and increased government regulation. Some of the most effective and cost-efficient emissions controls involve the use of downstream chemical catalysts that further oxygenate incompletely combusted compounds. Sometimes exhaust is directed sequentially through multiple catalyst beds. It is generally understood that higher catalyst temperatures provide more effective emissions control. Much exhaust catalysis development has been focused on developing catalytic converters for automotive applications, in which engine speed varies substantially with vehicle speed and gear selection.

In several other applications, such as in powering fixed-frequency electrical generators, engine speed is held as constant as possible during use, even while generator and engine loads fluctuate. Some engine-generator sets are designed for installation on-board moving vehicles, either on land or in water.

Marine generators are subjected to specific regulations, both for emissions and for safety concerns. For example, exposed engine surface temperatures (including exhaust system surface temperatures) must be kept low to avoid increased risk of fire hazard. Seawater is injected into many marine engine exhaust flows so as to cool exiting exhaust gases, and seawater is also frequently circulated through exhaust system components so as to maintain low surface temperatures.

Further improvements in exhaust emissions controls for constant and variable speed engine applications are desired, particularly improvements suitable for marine use.

SUMMARY

Many aspects of the invention feature methods of controlling emissions from an internal combustion engine.

In one aspect, the method includes governing engine speed with respect to a constant speed, maintaining an air/fuel ratio of the engine, flowing exhaust from the engine through an exhaust system containing a catalyst, monitoring a first variable with a feedback sensor located upstream of the catalyst, and controlling the air/fuel ratio of the engine as a function of the variable.

In some cases the first variable is oxygen and/or the feedback sensor is a narrow-band oxygen sensor. In some cases, the first variable is monitored with a MEMS device. In some embodiment, the method further includes monitoring a second variable with an exhaust sensor located downstream of the catalyst. In some embodiments, the second variable is carbon monoxide. In some other embodiments, the second variable is oxygen and/or the exhaust sensor is a wide-band oxygen sensor.

In a preferred embodiment, the air/fuel ratio is stoichiometric. In other embodiments, the air/fuel ratio is slightly lean. In some embodiments, the air/fuel ratio with is controlled with electronic fuel injection. In one embodiment, the electronic fuel injection is throttle-body fuel injection. In other embodiments, the electronic fuel injection is multi-point fuel injection. The the electronic fuel injection can be synchronized external fuel injection. Alternatively, the the electronic fuel injection can be nonsynchronized external fuel injection. In still other embodiments, the electronic fuel injection is direct fuel injection.

In one embodiment, the catalyst is configured to simultaneously reduce oxides of nitrogen, carbon monoxide and hydrocarbons. In some preferred embodiments, the catalyst is configured to reduce carbon monoxide to between about 9 parts per million and between about 30 parts per million. In one presently preferred embodiment, the catalyst is configured to reduce carbon monoxide to ambient levels.

In one embodiment, the engine is configured for marine applications and the exhaust system further comprises a water-jacketed manifold. In some cases, the engine is driving an electric generator. In one application, the generator is a multi-pole permanent magnet generator. In some embodiments, the generator is configured to operate at variable speeds. In some embodiments, the generator modulates between a high speed and a low speed having a ratio of 3 to 1. In other embodiments, the generator modulates between a high speed and a low speed having a ratio of 2 to 1.

In another aspect, the method includes driving an electric generator with the engine configured for marine applications, governing engine speed with respect to a selected constant speed, maintaining an air/fuel ratio of the engine, flowing exhaust from the engine through an exhaust system containing a catalyst, monitoring a first variable with a feedback sensor located upstream of the catalyst, the catalyst being configured to simultaneously reduce oxides of nitrogen, carbon monoxide and hydrocarbons, and controlling the air/fuel ratio of the engine as a function of the variable with electronic fuel injection.

In some embodiments, the method also includes monitoring a second variable downstream of the catalyst with an exhaust sensor downstream of the catalyst and providing a warning to an operator when the second variable reaches a threshold level. In some cases, the second variable is carbon monoxide. In other applications, the second variable is oxygen.

In some embodiments, the exhaust sensor is a wide-band oxygen sensor. In some embodiments, the generator is a permanent magnet generator. In some cases, the second variable is carbon monoxide. The other cases, the second variable is oxygen.

In a preferred embodiment, the air/fuel ratio is stoichiometric. In other embodiments, the air/fuel ratio is slightly lean.

DETAILED DESCRIPTION

Referring first toFIG. 1, an engine-generator set10includes an internal combustion engine12driving an electrical generator14. Engine10has an exhaust manifold16that receives and combines exhaust gasses from each cylinder of the engine and directs the combined exhaust gasses through a catalyst contained within the manifold, as is discussed in more detail below. Secured to the outlet of the manifold16is an exhaust elbow18. In a marine application, water, such as cold seawater, is supplied to manifold16through hose30. The water is directed through cooling passages in manifold16and elbow18to keep the outer surfaces of the exhaust system at or below a desired temperature, and is then injected into the exhaust stream in elbow18, downstream of the catalysts, to cool the exhaust.

In one embodiment, a variable is monitored with a feedback sensor19located upstream of the catalyst which provides a control signal to electronic controller24. In one embodiment, controller24provides controls the air fuel ratio of the engine12to correspond to a 1.0 stoichiometric ratio. In other embodiments, the air fuel ratio of the engine12is slightly lean. In one embodiment, the variable monitored by the feedback sensor19is oxygen and the feedback sensor19is a narrow-band oxygen sensor.

In one embodiment, an exhaust sensor23is mounted downstream of the catalyst. In one embodiment, the exhaust sensor23measures oxygen as a proxy for indirectly determining the level of carbon monoxide. In this application, a wide-band oxygen sensor can be used. In other applications, the exhaust sensor23directly measures carbon monoxide. The signal output from the exhaust sensor23can provide an anticipatory alarm apprising an operator when the catalyst32is functioning with reduced effectiveness. Accordingly, the exhaust sensor can inform the operator if the catalyst32has been damaged by seawater and requires replacement. The exhaust sensor23can be a MEMS device in some embodiments.

With continued reference toFIG. 1and in an alternative embodiment, air is delivered to manifold16, through a controllable dump valve20, from belt-driven air pump22. A fixed speed, electric air pump may also be employed. Valve20is controlled by an electronic controller24to moderate the flow of air into manifold16as a function of the load placed on engine12, such as by controllably dividing the output of the air pump between manifold16and exhaust elbow18. Controller24varies a signal to valve20as a function of engine load, or as a function of a sensible parameter that changes with engine load. In the illustrated embodiment, controller24senses an output voltage and/or current of generator14, such as at generator output26, and controls valve20accordingly. Controller24also senses engine speed, such as by receiving a signal from flywheel magnetic reluctance sensor28, and controls engine inputs (such as fuel and/or air flow) to maintain engine speed at or near a desired set point, so as to maintain the frequency of generator14. As an alternative to controlling a dump valve20splitting pump air flow between manifold16and either atmosphere or a lower point in the exhaust stream, a variable speed electric air pump22ais employed in some instances, with controller24varying the operating speed of pump22aas a function of engine load. In such cases, the entire output of pump22ais preferably ported directly to manifold16.

Referring to nowFIG. 2, a cylindrical catalyst32containing a catalyst bed is shown disposed within the exhaust manifold16. The catalyst32is wrapped in an insulating blanket96, such as a ⅛ inch (3.2 millimeter) thick sheet of cotton binding containing mica, for example, that helps reduce heat transfer from the catalyst into the housing and also helps to isolate the delicate catalyst bed from shocks and vibrations. In one embodiment, controlled air flow is injected either just forward of the catalyst at port38a, or at the far end of the manifold at port38bso as to preheat the injected air flow. Single catalyst32may be of any preferred composition, such as a palladium-platinum catalyst, for example. In other embodiments, no air flow injection is required.

With continued reference toFIG. 2and in one embodiment, catalyst32is configured and dimensioned for fitting within a marine exhaust manifold16. In one presently preferred embodiment, the catalyst32has a diameter of 3.66 inch (9.30 cm) and a length of 6.0 inch (15.24 cm). The catalyst32can include a round ceramic having a diameter of 3.0 inch (7.62 cm) and a length of 6.0 inch (15.24 cm) and a 400-cells per inch with 95-grams per cubic foot of a 3-to-1 ratio of platinum to rhodium. The catalyst32can also include a specialized wash coat designed to be the most effective at a 1.0 stoichiometric air fuel ratio. The catalyst32is configured to simultaneously reduce oxides of nitrogen, carbon monoxide and hydrocarbons. In one preferred embodiment, the catalyst32is configured to reduce carbon monoxides levels to below 50 part per million, preferably to below 35 parts per million, and most preferably to below ambient levels, i.e., 9 part per million.

Other catalyst configuration are contemplated within the exhaust manifold16. For example as illustrated inFIG. 3, the catalyst32in an alternative embodiment can include a first catalyst33and second catalyst36contained within a second bore of the manifold, parallel to and offset from the first bore. The manifold can be equipped with a removable cover44through which the air is injected, enabling loading of both of the catalysts into their respective bores. As in the first illustrated embodiment, after flowing through both catalyst beds the exhaust flow is combined with cooling water in elbow18a.

The exhaust is combined and directed through a first catalyst bed32, through a space34, and then through a second catalyst bed36. The air is injected into the manifold in space34, through air inlet38. Cooling water flows around both catalyst beds, through appropriate channels cast into manifold16aand elbow18, and is then injected into the exhaust flow. In marine applications where the cooling seawater can have a high salt content, the water injection outlets40in elbow18are preferably at least about six inches (15 centimeters) below the lowest edge of the catalysts or the upper edge of any internal elbow baffles42positioned to avoid salt water splash on the hot catalysts. Also, it is preferred that for such marine applications manifold16aand elbow18be cast of a corrosion-resistant material, such as an aluminum-magnesium alloy. It will be apparent fromFIG. 2that the connection between manifold16aand elbow18can be readily positioned between the two catalyst beds, such that second catalyst36is carried within elbow18.

The construction of the catalyst32according to this embodiment can include a first catalyst bed33which preferably includes a catalyst such as one containing rhodium as the precious metal, selected to reduce hydrocarbon and NOxemissions. For example, one preferred catalyst bed is in the form of a cylinder 3.0 inches (76 millimeters) in diameter and 2.6 inches (6.7 centimeters) long. The ceramic substrate has a cross-sectional area of about 7 square inches (45 square centimeters) and has about 400 cells per square inch (62 per square centimeter), and is washed with 6.1 grams per cubic foot (0.06 grams per cubic centimeter) of rhodium. Such a catalyst bed is available from ASEC/Delphi Exhaust and Engine Management of Flint, Mich. Catalysis efficiency within first catalysis bed33may be accomplished by various methods known in the art, either in carbureted or fuel-injected systems with oxygen sensors, to remove as much of the overall emissions components as possible.

The second catalyst bed36contains a catalyst selected to further reduce CO emissions. In one arrangement, second catalyst bed36contains a three to one ratio of palladium and platinum, carried on a honey-combed substrate of ceramic or metal. The active precious metals are washed onto the substrate and then heated to set the metals onto the surface as known in the art. An example of a preferred second catalyst bed is a metal substrate in the form of a cylinder of 5.0 inch (12.7 centimeter) diameter and 6.3 inch (16 centimeter) length, with 19.6 square inches (126 square centimeters) of cross-sectional area, washed with 40 grams per cubic foot (0.4 grams per cubic centimeter) each of palladium and platinum. Such a catalyst is available from Miratech of Tulsa, Okla., for example. Second catalyst36will tend to run hotter, such as perhaps about 400 degrees Fahrenheit (220 degrees Celsius) hotter than the rhodium catalyst. Preferably, the temperature of the combined air and exhaust entering the second catalyst is about 1000 degrees Fahrenheit (540 degrees Celsius).

FIGS. 4 and 5show another example of a catalyst exhaust manifold16b. The catalyst32is loaded as a cylinder from the large end of the manifold, with the NOxcatalyst loaded into bore46(FIG. 5) and the CO catalyst loaded into bore48(FIG. 5). In this example, coolant enters the manifold at inlet50and leaves the manifold at outlet52, without joining the exhaust stream. The cooling channels54cast into the manifold are partially shown inFIG. 5, providing a closed flow path between inlet50and outlet52.

Various control techniques may be employed to vary air injection rate for good CO reduction. In one embodiment, the air injection rate is varied as a function of approximate engine load. In one test using a Westerbeke 4-cylinder, 1.5 liter gasoline engine and the palladium-platinum second catalyst bed described above, the lowest CO emissions were provided by varying the rate of air flow into the manifold ahead of the second catalyst (at 100 liter per minute graduations) according to the following table:

Engine Load (Percent Full Load)Air Flow Rate (liters per minute)100500755005050025400103000300

Of course, optimal air flow rates will be different for different applications. The air flow controller can be configured to interpolate between adjacent entries in the load-air correlation table to provide finer control sensitivity.

There are various ways to determine approximate engine load, such that a table like that shown above can be used to determine an optimal air injection rate. For example, if substantially all of the engine load is provided by an electrical generator (as shown inFIG. 1), monitoring the electrical output of the generator can provide a good estimate of engine load. Current can be monitored as a most direct measure of electrical load, such as by providing a current transformer about the output of the generator. In some cases in which generator voltage is known to predictably decrease a measurable amount with load, voltage may alternately be monitored. In most cases, however, current monitoring is preferred for systems with proper generator voltage regulation. Other options include measuring engine output driveshaft torque (or some measurable parameter that varies predictably with torque), or measuring the pressure within the manifold, such as upstream of the catalyst beds, or exhaust backpressure below the catalysts and above a muffler or other exhaust restriction. Because the engine speed is substantially fixed in the primary embodiments, other parameters may also be found to vary predictably with engine load, such as throttle position and fuel flow rate, for example.

As an alternative to controlling the air injection rate as a function of load, the air injection rate can be controlled as a function of other measured parameters that signify catalysis efficiency. For example, a CO sensor may be provided downstream of the catalyst as described above.

With renewed reference toFIG. 2an in one embodiment, an exhaust pressure sensor62can be placed in the manifold16, to measure exhaust manifold pressure, or downstream of the catalyst32to measure exhaust backpressure developed upstream of a muffler or other exhaust restriction (not shown). If the air pump delivering air to inlet38is not a fixed displacement pump, changes in exhaust backpressure with engine load can cause a significant fluctuation in the injected air rate. This fluctuation will tend to work against the desired variation of air flow rate with engine load, as backpressure, which rises with engine load, will cause a reduction in air injection rate that should be accounted for in the control of the pump or valve. It will be understood that sensors62are shown in optional and alternative locations, and are not necessary in some embodiments, such as when air flow rate is controlled as a function of generator current or some other primary control parameter.

Referring now toFIG. 6, an exhaust system60for the engine12mounted in a boat67is shown. The exhaust manifold16directs exhaust gases through the catalyst32and exhaust elbow18and past a water injected exhaust elbow65. To reduce the operating temperature of the exhaust components, cooling seawater is injected at the inlet to the exhaust elbow70. The exhaust gases and cooling water then pass through an exhaust valve and water level indicator75(discussed in more detail below). The exhaust gasses and cooling water enter a water lift marine muffler80before proceeding to a high point at the U-bend85and out of the boat through the through-hull fitting90above the water line97. In one embodiment, the muffler80includes a drain97.

In marine applications, it is desirable to prevent cooling seawater from contacting the catalyst32disposed within the exhaust manifold16. It is also desirable to prevent cooling seawater from reaching the engine12, which can results in catastrophic failure. Referring toFIG. 7, an exhaust valve and water level indicator75are shown and disposed within the marine exhaust manifold16between the water injected exhaust elbow65and the water lift muffler80(FIG. 6). The valve/indicator75can include a float valve105, such as a ball valve and a water level indicator110combined in a housing115. The ball valve105translates along the housing115between ball valve guides120a,120band is supported by ball valve supports130a,130bwhen the ball valve is disposed in an open position135(shown in phantom). When the ball valve105ascends upward to the closed position (as shown) the surface of the ball valve105contacts the housing115along valve sealing areas140a,140bthereby closing the valve. The rising water level within the housing115floats the water level indicator110upward to an alarm level which provides a signal145to warn an operator that the muffler80is overfilled.

A number of embodiments of the invention have been described. For example, the engine12as described above can be used for propulsion in marine applications. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.