Patent Application
20060289308
The invention relates generally to an exhaust gas sensor system and, more specifically, to a system and method for protecting an exhaust gas sensor from particulate emissions.
Vehicle and industrial exhaust emissions typically include carbon monoxide, oxides of nitrogen, hydrocarbons and particulates, carbon dioxide, or the like. These substances are a significant contributor to local air pollution, which may result in poor visibility, including smog, and haze and erosion of building surfaces.
Because of concerns about pollution, many vehicles and industrial systems include devices to help reduce the emission of undesirable substances. Such devices typically include an exhaust sensor that detects a level of undesirable substances in the exhaust stream. Exhaust sensors may be adapted to measure levels of oxygen, hydrocarbons and nitrous oxides in the exhaust stream. Sensors may also be used to sense, for example, when an exhaust gas content switches from rich to lean, or lean to rich. The output of the exhaust sensor may be used by a combustion control unit to improve the quality of the exhaust stream by controlling various combustion unit parameters.
Constituents of exhaust gas such as particulates, and water droplets may foul the exhaust gas sensing device, resulting in degraded performance of the emission control device. For example, a fouled sensor may have reduced ability to accurately detect the constituent components of an exhaust gas stream. Shielding the sensor from direct contact with large particulate matter in the exhaust stream may reduce the occurrence of sensor fouling.
While preventing fouling of the exhaust sensor is important, a countervailing design consideration is to ensure sufficient airflow in the vicinity of the exhaust gas sensor. Sufficient flow is required to allow the sensor to provide an accurate reading in a given response time to facilitate effective control of the combustion unit.
An improved system and method for balancing the competing design goals of providing sufficient flow past an exhaust gas sensor while protecting the sensor from being fouled by large particles in the exhaust stream is desirable.
In accordance with one aspect of the present technique, an exhaust gas sensor system is provided. The exhaust gas sensor system includes an inner chamber disposed around a sensor element. The system further includes an outer chamber substantially disposed around the inner chamber to redirect a flow of an exhaust gas stream having an original direction by allowing the exhaust gas stream to strike a surface of the inner chamber to change the original direction of the flow to a substantially perpendicular direction relative to the original direction, then to substantially reverse the substantially perpendicular direction of the flow to create a substantially reversed flow within the inner chamber.
In accordance with another aspect of the present technique, an exhaust gas sensor system is provided. The exhaust sensor system includes a sintered metal filter that prevents exhaust gas particles from fouling a sensor element. The system further includes an electric source coupled to the sintered metal filter to heat the sintered metal filter to a temperature sufficient to remove the exhaust gas particles from the sintered metal filter.
In accordance with another aspect of the present technique, a method of operating an exhaust gas sensor system is provided. The method includes directing a flow of an exhaust gas stream having an original direction through an opening formed at one end of an outer chamber. The method further includes redirecting the flow of the exhaust gas stream having the original direction by allowing the exhaust gas stream to strike a surface of an inner chamber substantially disposed within the outer chamber to change the original direction of the flow to a substantially perpendicular direction relative to the original direction, then to substantially reverse the substantially perpendicular direction of the flow to create a substantially reversed flow within the inner chamber.
In accordance with another aspect of the present technique, a method of operating an exhaust gas sensor system is provided. The method includes directing a flow of an exhaust gas stream to a sensor element via a sintered metal filter so that exhaust gas particles are trapped within the sintered metal filter. The method further includes heating the sintered metal filter via an electric source to remove the accumulated exhaust gas particles from the sintered metal filter.
These 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.
Referring to
An intake manifold 24 is coupled to the combustion chambers of the respective cylinders 16. The intake manifold 24 is coupled to an intake pipe 26. A throttle valve 28 is provided in the intake pipe 26 and located upstream of the intake manifold 24. The throttle valve 28 is configured to adjust flow rate of intake air through the intake pipe 26. An intercooler 29 is provided in the intake pipe 26 to cool the intake air through the intake pipe 26. A throttle actuator 30 such as a step motor may be coupled to the throttle valve 28 and configured to actuate the throttle valve 28.
An exhaust manifold 32 is coupled to the combustion chambers of respective cylinders 16. A fuel addition valve (not shown) may be provided in the exhaust manifold 32 for injecting fuel into the exhaust gas flowing through the exhaust manifold 32. An exhaust gas sensor system 34 is provided within an exhaust pipe 36 coupled to the exhaust manifold 32. The exhaust gas sensor system 34 may include an exhaust sensor element 38 adapted to measure levels of oxygen, hydrocarbons and nitrous oxides, or the like in an exhaust gas stream. Constituents of the exhaust gas stream such as soot particles, water droplets or the like may foul the exhaust sensor element 38 that may inhibit the ability of the sensor element 38 to detect the presence of gases effectively. The exhaust gas sensor system 34 includes features in accordance with the present technique, to protect the exhaust sensor element 38 against direct exposure to exhaust gases while helping to provide sufficient gas flow to the sensor element 38 to meet response time requirements necessary to effectively operate an engine control system.
In alternate embodiments, the exhaust gas sensor system 34 may be provided within an exhaust unit of an industrial system such as boilers, gas turbines, or the like. The exhaust gas sensor system 34 includes features in accordance with the present technique, to protect the exhaust sensor element 38 against exposure to exhaust gas particles such as soot particles, ash, or the like while helping to provide sufficient gas flow to the sensor element 38 to meet response time requirements necessary to effectively operate a combustion control unit.
Referring to
The outer chamber 42 is provided around the inner chamber 40 in such a way so as to redirect the flow of the exhaust gas stream. In the illustrated embodiment, the exhaust gas stream having an original direction (i.e. substantially perpendicular to the inner and outer chambers 40, 42) passes through the plurality of openings 44 in the outer chamber 42 and strikes a peripheral surface 56 of the inner chamber 40. The flow of the exhaust gas stream is redirected from the original direction to a substantially perpendicular direction relative to the original direction. The substantially perpendicular direction of the flow is then reversed to create a reversed flow within the inner chamber 40 by virtue of the fact that the exhaust gas stream enters through the inlet opening 48 and exits through the outlet opening 52 of the inner chamber 40. As a result, larger exhaust gas particles in the exhaust stream are prevented from entering the inner chamber 40 due to change in direction of the exhaust gas stream. Smaller particles in the exhaust gas stream reaching the sensor element 38 may be burned due to higher temperature prevailing around the sensor element 38. The exhaust gas particles may also be collected on the peripheral surface 56 of the inner chamber 40 due to thermophoresis effect. Thermophoresis occurs because of the movement of particles from a hotter region to a colder region. The exhaust sensor element 38 is protected from damage without compromising on the response time of the sensor element 38.
Referring to
As described above, the outer chamber 42 is provided around the inner chamber 57 in such a way so as to redirect the flow of the exhaust gas stream. In the illustrated embodiment, the exhaust gas stream having an original direction (i.e., perpendicular to the inner and outer chambers 57, 42) passes through the plurality of openings 44 in the outer chamber 42 and strikes a peripheral surface 66 of the inner chamber 57. The flow of the exhaust gas stream is redirected from the original direction to a substantially perpendicular direction relative to the original direction. The substantially perpendicular direction of the flow is then reversed to create a reversed flow within the inner chamber 57, i.e., the exhaust gas stream enters through the inlet opening 58 and exits through the outlet opening 62 of the inner chamber 57. As a result, larger exhaust gas particles in the exhaust stream are prevented from entering the inner chamber 57 due to change in direction of the exhaust gas stream. The provision of frusto-conical shaped inner chamber 57 facilitates larger flow of exhaust gas into the inner chamber 57. The stagnation of exhaust gas between the inner chamber 57 and the outer chamber 42 is also reduced.
In the embodiments illustrated above, the inner chamber 57 is substantially enclosed within the outer chamber 42. As a result, the sensor element 38 is adequately protected. Moreover, the exhaust gas sensor system 34 is less susceptible to vibrational failures. Exhaust gas particles in the exhaust stream are prevented from entering the inner chamber 57 due to change in direction of the exhaust gas stream. In one example, soot particles of size greater than 50 microns may be removed in the outer chamber 42.
Referring to
The exhaust gas stream strikes the periphery 86 of the inner chamber 68 and enters through an annular gap 88 between the inner chamber 68 and the outer chamber 78. The exhaust gas stream is redirected from the inclined end 80 of the outer chamber 78 into the inner chamber 68. The exhaust gas passes through the inner chamber 68 and then exits through the outlet opening 84 formed in the outer chamber 78. As a result, larger exhaust gas particles in the exhaust stream are prevented from entering the inner chamber 68 due to change in direction of the exhaust gas stream. The exhaust gas particles are collected at the inclined end 80 of the outer chamber 80 and drained through the holes 82 formed in the outer chamber 78.
Referring to
where T is the response time, h is height of inner chamber, v is the velocity of exhaust gas stream, and D is the diameter of the inner chamber.
It may be inferred from the graph that the sensor response time is improved when the diameter of the inner chamber is reduced. In accordance with the exemplary embodiment illustrated in the graph, the exhaust gas sensor system 34 in which frusto-conical shaped inner chamber 56 is provided within the outer chamber 42 gives a faster response. For example, for detecting about 70 percent change in concentration of exhaust gas, the exhaust sensor element 38 takes approximately 400 milli-seconds.
Referring to
The sintered metal filter 98 is configured to prevent exhaust gas particles from reaching the exhaust sensor element 38. The sintered metal filter 98 may comprise iron, chromium, nickel, steel, or a combination thereof. The sintered metal filter 98 may have higher electrical resistivity and good heat conducting properties. Although in the illustrated embodiment the filter 98 is a closed end tube, the filter may have other suitable configurations in other embodiments. The outer protective shell 100 is provided to protect the filter 98 from external contaminants such as moisture, water, or the like. The outer protective shell 100 may include plurality of holes or slots for allowing passage of exhaust gas stream.
Referring to
When the exhaust gas stream is passed through the sintered metal filter 98 to the sensor element 38, exhaust gas particles such as soot, ash particles, or the like within the exhaust gas stream is trapped within the filter 98. The filter 98 needs to be cleaned at predefined intervals or continuously to burn the soot particles trapped within the filter 98. If the filter 98 is not cleaned periodically, pressure drop across the filter 98 is increased, thereby reducing the amount of gas reaching the sensor element 38. As a result, response time of the sensor element 38 becomes slower. As discussed above, the current from the DC source 110 is passed through the filter 98 to directly heat the filter 98. Direct heating of the filter 98 enables the filter 98 to be maintained at higher temperatures to burn the soot particles trapped within the filter 98. In one example, the filter 98 may be maintained at a temperature in the range of 550 to 600 degrees celsius to ensure the burning of soot particles. For industrial applications, a purge air source may be used to inject pressurized air to remove ash particles trapped within the filter 98.
Referring to
The exhaust gas stream having an original direction is allowed to strike the peripheral surface of the inner chamber as represented by step 126. The exhaust gas stream is redirected to change the original direction to a direction substantially perpendicular to the original direction. Thus, the gas stream flows axially via the gap between the inner and outer chambers. In one embodiment, the exhaust gas stream is redirected into the inner chamber by the inclined end of the outer chamber. The exhaust gas stream is then redirected through the inner chamber as represented by step 128. Thus, the exhaust gas stream enters through the inlet opening and exits through the outlet opening of the inner chamber. As a result, larger exhaust gas particles in the exhaust stream are prevented from entering the inner chamber due to change in direction of the exhaust gas stream.
Referring to
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
