Exhaust gas recirculation cooler bypass

A method including selectively injecting non-cooled exhaust gas into a primary air intake conduit at a first location; selectively injecting cooled exhaust gas into the primary air intake conduit at a second location; and wherein the second location is downstream from the first location with respect to the direction of gas flow in the primary air intake conduit.

TECHNICAL FIELD

The field to which the disclosure generally relates includes exhaust gas recirculation systems including coolers and methods of operating the same.

BACKGROUND

The performance of a combustion engine can be improved utilizing a turbocharger including a turbine side and a compressor side. Improvement in the emissions from such a combustion engine can be achieved with exhaust gas recirculation. However, for low pressure exhaust gas recirculation systems, high flow rates of the exhaust gas being recirculated can lead to high compressor inlet temperatures. An exhaust gas cooler may be positioned to reduce the temperature of the exhaust gas prior to the compressor inlet. However, such systems can lead to condensation of water vapor in the exhaust gas and wherein the resultant water droplets damage the compressor wheel which is spinning at a relatively high rpm.

High pressure applications of exhaust gas recirculation provide a recirculation flow path for the exhaust gas before the exhaust goes through a turbocharger (if present). Coolers have been used in such high pressure recirculation systems, but under certain circumstances such systems may produce undesirable constituents in the gas or lead to undesirable engine performance.

SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION

One embodiment of the invention includes a method of operating a breathing system for a combustion engine comprising selectively injecting non-cooled combustion engine exhaust gas into a primary air intake conduit at a first location, selectively injecting cooled combustion engine exhaust gas into the primary air intake conduit at a second location and wherein the second location is downstream of the first location with respect to the direction of flow of gases in the primary air intake conduit.

Another embodiment of the invention includes a product comprising: an exhaust gas recirculation line and a first exhaust gas cooler in fluid communication with the first primary exhaust gas recirculation line; a bypass line constructed and arranged to provide a flow path for recirculation exhaust gas around the cooler; and wherein the bypass line includes a first end constructed and arranged to be connected to a primary air intake conduit at a first location, and wherein the first primary exhaust gas recirculation line is constructed and arranged to be connected to the primary air intake conduit at a second location downstream from the first location.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description of the embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Referring now toFIG. 1, one embodiment of the invention includes a product or system10. The product or system10may include one or more of the following components. The system10may include a combustion engine18constructed and arranged to combust a fuel, such as but not limited to, diesel fuel in the presence of oxygen (air). The system10may further include a breathing system including an air intake side14and a combustion exhaust gas side16. The air intake side14may include a manifold20connected to the combustion engine18to feed air into cylinders of the combustion engine18. A primary air intake conduit22may be provided and connected at one end23to the air intake manifold20(or as a part thereof) and may include an open end24for drawing air therethrough. A filter26may be located at or near the open end24.

The combustion exhaust side16may include an exhaust manifold28connected to the combustion engine18to exhaust combustion gases therefrom. The exhaust side16may further include a primary exhaust conduit30having a first end32connected to the exhaust manifold28(or as a part thereof) and having an open end34for discharging exhaust gas to the atmosphere.

The system10may further include a first exhaust gas recirculation assembly36extending from the combustion exhaust gas side16to the air intake side14. A first exhaust gas recirculation (EGR) valve38may be provided in fluid communication with the primary exhaust gas conduit32and constructed and arranged to control the flow of exhaust gas out of the open end34of the primary exhaust conduit30and to control the flow of exhaust gas through a first EGR assembly36. The first EGR assembly36may include a first primary EGR line40having a cooler42in fluid communication therewith for cooling the exhaust gas flowing through the first primary EGR line40. The cooler42may include an inlet44and an outlet46to facilitate the flow of a coolant such as water or an anti-freeze fluid known to those skilled in the art. The coolant may be the same as that used to cool the combustion engine and may flow to the engine radiator or to a separate radiator. The first EGR assembly36may further include bypass line48constructed and arranged to allow exhaust gas to flow past the cooler42. In one embodiment of the invention, the bypass line48is connected to the first primary EGR line40at a bypass valve50. The bypass valve50may be provided in the first primary EGR line40upstream of the cooler42. Alternatively, a bypass valve50may be positioned downstream of the cooler42and is constructed and arranged to control the flow of exhaust gas through the first primary EGR line40and the bypass line48. In still another embodiment of the invention, the bypass line50may be directly connected to the primary exhaust conduit30and may include a control valve in the bypass line48or the primary exhaust conduit30for controlling the flow of exhaust gas through the bypass line48.

The bypass line48connects to the primary air intake conduit22at a first location52which is downstream of the open end24of the primary air intake conduit22. The first primary EGR line40of the first EGR assembly36connects to the primary air intake line22at a second location54which is downstream of the first location52but upstream of the compressor62(if present). As will be appreciated from the schematic illustration ofFIG. 1, the temperature TCin the bypass line48at or near the first location52is greater than the temperature TBin the first primary EGR line40at the second location54after the exhaust gas has been cooled by the cooler42. Incoming air entering the primary air intake conduit22through the open end24has an initial temperature T0. The air flowing in the primary conduit22is warmed by the exhaust gas flowing through the bypass line48such that the temperature of the gases flowing in the primary air intake conduit22has a temperature TAat a position slightly downstream of the first position52. The fresh air entering through the open end24and the exhaust gas in the bypass line48have sufficient time to mix prior to the cooled gas, from the first primary EGR line40, entering the primary air intake conduit22at the second location54. The first EGR assembly36and operation thereof may be utilized to control the temperature T1of the gases flowing in the primary air intake conduit22at a location downstream of the second position54. The first EGR assembly36may be utilized for low-pressure exhaust gas recirculation and/or high-pressure exhaust gas recirculation.

In one embodiment of the invention the system10includes a turbocharger58having a turbine60in fluid communication with the primary exhaust conduit30and having a compressor62in fluid communication with the primary air intake conduit22to compress gases flowing therethrough. The first EGR assembly36is particularly well suited for this embodiment in that the first EGR assembly36can be utilized to control the temperature T1of the gas flowing in the primary air intake conduit22at a location just prior to the gas entering the compressor62. Although it is desirable to cool the exhaust gas prior to entry into a compressor62, such may result in the condensation of water vapor in the exhaust gas. The resulting water droplets may cause serious damage to the blades of the compressor62which is rotating at a relatively high rpm. Further, it has been discovered that connecting the bypass line48to the primary air intake line22upstream of the injection of the cooled exhaust gas, from the first primary EGR line40, results in the warming of the incoming air to a temperature sufficiently above T0. As such, the injecting of cooled exhaust gas from the first primary EGR line40into the primary air intake line22can be managed to substantially reduce or eliminate condensation.

Optionally, a second EGR assembly64may be provided for high-pressure exhaust gas recirculation. The second EGR assembly64may be identically constructed as the first EGR assembly36if desired. As shown inFIG. 1, in one embodiment of the second EGR assembly64, a second EGR line66extends from the primary exhaust gas conduit30to the primary air intake conduit22. A second EGR valve68is provided to control the flow of exhaust gas through the second EGR line66. If desired, an EGR cooler70may be provided in fluid communication with the second EGR line66to cool exhaust gases flowing therethrough.

The system10may include a variety of further components as desired. For example, the primary exhaust gas conduit30may include additional emission components such as, but not limited to, a particulate filter72which may be positioned downstream or upstream of the turbine60and upstream of the first EGR valve38. The air intake side14may include a second charge air cooler74upstream of the compressor62and a throttle valve76positioned in the primary air intake conduit22, for example, at a location between the second charge air cooler74and the connection of the second exhaust gas recirculation line66to the primary air intake line22. Furthermore, the system10may include a controller system82, such as an electronic control unit, including memory devices and data processing devices. The controller system82may be electronically connected to at least the first EGR valve38and the bypass valve50to control the same in response to a variety of inputs. Such inputs may include, but are not limited to, a signal or data, such as engine speed and load provided from the engine by an engine sensor78, or a signal or data provided regarding exhaust gas constituents such as the level of oxygen, NO2and particulate matter provided by an exhaust gas sensor80. Temperatures T0, T1, T2, TA, TB, TC, TDand TEmay be measured or calculated values and such information may be utilized by the controller system82to control the first EGR valve38and the bypass valve50.

Referring now toFIG. 2, depending upon the speed and load (engine operating point) either T1or T2can be controlled utilizing the first EGR assembly36. The temperature set points for T1, T2can be set individually for each engine operating condition.FIG. 2shows four different engine operating points. For the two operating points B and D, the temperature T1may be controlled to a set point and temperature T2may float. For the two operating points A and C, the temperature T2may be controlled to a set point, and temperature T1may float. The temperatures of the gas in the system10at various locations are controlled by actuating the first EGR valve38and the bypass valve50.

The flow of exhaust gas through the first EGR assembly36may be controlled so that the compressor inlet temperature T1may be maintained within a predetermined range or to a specific set point, and likewise the compressor outlet temperature T2may be maintained within a predetermined range or to a specific set point. For example, the temperature T1may be controlled within a range of 50° C. to about 100° C. or to a set point of about 70° C. Likewise, the compressor outlet temperature T2may be controlled to a range of about 100° C. to about 200° C. or to a set point of about 150° C. By controlling the flow through the first EGR assembly36, condensation of the low pressure exhaust gas recirculation fraction coming out of the exhaust gas recirculation cooler42in the mixing area in front of the compressor62may be eliminated or substantially reduced.

Referring again toFIG. 1, the non-cooled exhaust gas recirculation fraction passing through the bypass line48is mixed first with fresh air entering through opening24. The mixing takes place in the intake conduit22upstream of the connection of the first primary EGR line40which includes cooled exhaust gas. The air intake/non-cooled exhaust gas recirculation mixture is then mixed with the cooled exhaust gas recirculation fraction passing through the exhaust gas recirculation cooler42. This mixing takes place in the primary air intake conduit22, but a certain distance downstream of a mixing of the non-cooled fraction from the bypass line48with the fresh air. The distance between the bypass conduit48and the primary line40including cooled exhaust gas is necessary to provide for adequate mixing. The calculated temperature of the mixture in the air intake conduit at all times during the mixing is above a threshold value. This threshold value is dependent upon the temperature and the absolute humidity of fluids before and at every point during mixing. These temperatures can be either estimated through maps in the ECU or measured by temperature sensors for T1and TA.

The flow of exhaust gas through the first EGR assembly36may be controlled under a variety of circumstances and in a variety of manners. For example, the control system82may receive inputs related to temperatures T0, TA, TB, TC, TD,T1or engine speed or load. In response thereto, the controller82output may cause the low-pressure first EGR valve38to open to allow exhaust gas to flow through the first EGR assembly36. The bypass valve50may be controlled to split exhaust gas flow between gas traveling through the cooler42and gas through the bypass line48.

In one embodiment of the invention, the amount of exhaust gas fraction flowing through the cooler42is limited until the coolant temperature flowing through the cooler42exceeds a certain value. The exhaust gas recirculation fraction limit will allow estimating the amount of condensate coming out of the cooler42. The amount of condensate coming out of the cooler42is, but is not limited to, a function of the coolant temperature in the exhaust gas recirculation cooler42, the exhaust gas recirculation mass flow rate and the absolute humidity of the exhaust gas. As such, in one embodiment of the invention, the controller system82may receive an input regarding the coolant temperature of the cooler42, for example from a coolant sensor84constructed and arranged to measure the temperature or estimate the temperature of the coolant in the cooler48. The controller system82would provide an output causing the low-pressure first EGR valve38to move to control the low-pressure exhaust gas mass flow rate traveling through the first EGR assembly36and cause the bypass valve50to move to a position to split the flow of exhaust gas through the bypass line48and through the cooler42.

Another embodiment of the invention includes a method of limiting the intake temperatures TAand T1within certain boundaries TAminT1min, T1max, for example as illustrated inFIG. 3. The flow of exhaust gas through the bypass line48is controlled so that the estimated temperature TAafter mixing the non-cooled exhaust gas with the fresh air entering through opening24has reached a minimum value TAmin. The minimum value of TAminmay vary depending upon operating condition of the system, including actual sensed or mapped based values of various operating conditions. Maintaining TAat a minimum value can help reduce condensation during mixing of the low-pressure exhaust gas fraction passing through the cooler42. The function of maintaining TAat a minimum can be overruled by the constraint of limiting the compressor inlet temperature T1to its maximum value of T1max. In such a case, cooled low-pressure exhaust gas recirculation flowing through the cooler42may be controlled to keep T1below T1maxby controlling the bypass valve50. The amount of cooled exhaust gas flowing through the cooler42may be controlled to keep temperature T1(measured or estimated from the exhaust gas recirculation rate, TAand TB) equal to or less than T1max(map based value, which may be a function of exhaust gas recirculation rate, TAand TB). This can help minimize or avoid condensation during mixing of the cooled low-pressure exhaust gas fraction flowing through the cooler42and into the primary air intake conduit22. The bypass valve50may be controlled to prevent exhaust gas from flowing through the cooler42until the cooler water temperature, which in one embodiment, may be estimated from the engine water temperature, is above a predetermined value Z° C.

In another embodiment, the flow of exhaust gas through the cooler42and through the bypass line48is controlled so that a certain value T1set(set point temperature before the compressor62) can be achieved. T1setcan be, but is not limited to, a function of engine speed and load and can be a consequence of temperature limits of the components of the system10.

In another embodiment, the flow of exhaust gas through the cooler42and the bypass line48may be controlled so that a certain value T2set(set point temperature after the compressor62) is achieved. The value T2setcan be, but is not limited to, a function of engine speed and load and can be a consequence of temperature limitations on the components in the system10. The values of T1setand T2setmay vary over the engine speed and load map. Using the bypass line48connected to the primary air intake conduit22at a first position to inject non-cooled exhaust gas upstream of the injection of cooled exhaust gas (passing through the cooler42) allows the gas temperature to be adjusted quickly to achieve desired temperatures for T1and T2. Although the flow of coolant through the cooler42could be varied to eventually change the temperature at T1and T2, such an adjustment may result in a change of T1and T2, but only over a substantially lengthy period of time. Furthermore, reducing the flow of coolant through the cooler42may result in the undesirable boiling of the coolant. In contrast, the temperatures T1and T2can be increased rather rapidly by increasing the flow rate of exhaust gas through the bypass line48or decreased by restricting or preventing the flow of exhaust gas through the bypass line48and only allowing flow through the cooler42.

The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.