Patent Application
20090260605
The present disclosure generally relates to diesel engines and more particularly to the arrangement of coolers utilized in exhaust gas recirculation in diesel engines.
Diesel engines include cylinders that combust a mixture of compressed air and diesel fuel. Frequently, exhaust gas recirculation (EGR) is utilized to minimize unfavorable emissions, such as NOx emissions, for the combustion of the diesel fuel. The usage of exhaust gas recirculation often impacts fuel economy, especially in turbocharged diesel engines. Moreover, in large duty trucks, the extra heat energy transferred to the coolant requires that the size of the radiators and cooling fans generally be increased in order to maintain engine temperature.
Traditionally, EGR systems have been described as a “high pressure loop” wherein the exhaust is extracted on the high-pressure side of a turbocharger turbine. The exhaust is then returned to the high pressure side of the turbocharger compressor. Accordingly, in order for the exhaust gas to flow in the proper direction, the exhaust manifold pressure must be higher than the intake manifold pressure. In order to achieve this, crankshaft power may be used to deliver power during the pumping loop portion of the engine cycle. Since the EGR in a high pressure loop requires a reversal of the manifold pressure differential as compared to normal engines, the pumping loop portion of the cycle consumes power, rather than delivers power. Thus, the amount of power consumed in the pumping loop portion depends upon the manifold pressure differential. In addition, the flow restriction of the EGR path may also affect the manifold pressure differential.
Much of the flow restriction of an EGR system occurs in the EGR cooler. The size of the cooler generally depends upon several factors. For example, the system may require a cooler large enough (i.e. with sufficient surface area for heat transfer) to deliver low temperature EGR at high power/high flow conditions in order to prevent NOx limits from being exceeded. Unfortunately, large coolers often result in a larger pressure drop, and further require more space for mounting. Moreover, at low power/low flow, the gas flowing through the cooler may deposit soot on the cooler surfaces. As these deposits build up on the surface of the cooler, the deposits insulate the surfaces and impede heat transfer. During laminar flow, the deposits may accumulate to the point where the flow passages become completely blocked, but with turbulent flow, the deposits stabilize at a certain thickness and typically do not block the passages of the cooler.
Furthermore, the first portion of the cooler generally provides a greater reduction in air temperature than the second portion downstream from the first portion. At relatively higher power, the reduction of temperature in the second portion may be necessary to cool the gas, but at lower power with the initial temperature of the gas being lower, the second portion may not effectively cool the gas but still reduce the pressure of the gas as it passes through the cooler.
Additionally, as mentioned above EGR cooler designs attempt to accommodate the lower emission requirements by increasing cooling of the EGR gas, which requires a larger cooler. The increase in cooler package size has reduced the available space for other components on the “hot side’ of the engine. Accordingly, it is desirable to increase the effectiveness of the EGR cooler, while maintaining a compact package configuration.
An embodiment of the present disclosure relates to a compression ignition engine comprising at least one combustion chamber, an air intake system, a fuel system, an exhaust system and an exhaust gas recirculation system. In one variation, the air intake system conveys air to at least one combustion chamber. In addition, the fuel system conveys fuel into at least on combustion chamber. Furthermore, the exhaust system conveys exhaust gases from at least one combustion chamber. The exhaust gas recirculation system is capable of recirculating a portion of the exhaust gases into the air intake system. The exhaust gas recirculation system comprises a first exhaust gas recirculation cooler, a second exhaust gas recirculation cooler and a valve positioned intermediate the first cooler and the second cooler. The valve, when opened, allows the exhaust gas to flow in parallel through both the first cooler and the second cooler. When closed, the valve prevents exhaust gas from flowing through the second cooler.
In one variation of the disclosure, the first cooler and the second cooler are liquid cooled. The first cooler is arranged in a parallel relationship with the second cooler. In another variation, a controller is capable of controlling whether the valve is opened or closed. In an extension of this variation, the controller includes a sensor configured to determine the speed of the engine.
In another variation of the disclosure, the engine further includes a third exhaust gas recirculation cooler connected to the first and second exhaust gas recirculation coolers. The third exhaust gas recirculation cooler is further connected to the intake, and the third exhaust gas recirculation cooler is connected in series with the first and second exhaust gas recirculation coolers. In yet another variation, the third exhaust gas recirculation cooler is air cooled. It should be understood, however, that any of the exhaust gas recirculation coolers may be liquid cooled, air cooled, or cooled using any other suitable technique.
As such, a staged arrangement EGR cooler according to the teachings of the present disclosure may incorporate a pair of independent cooler sections and a valve to control the amount of cross-sectional cooler area (by directing EGR gas to one or both cooler sections) as a function of engine load. Additionally, the EGR cooler package may be formed in a compact shape (such as a U-shape) to reduce the space required for mounting the cooler package and permit alternate mounting orientations (e.g. vertical instead of horizontal).
The features and advantages of the present disclosure described above, as well as additional features and advantages, will be readily apparent to those skilled in the art upon reference to the following description and the accompanying drawing.
The above-mentioned and other features of this disclosure and the manner of obtaining them will become more apparent and the disclosure itself will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawing, wherein:
Although the drawings represents embodiments of various features and components according to the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the concepts presented herein. The exemplifications set out herein illustrate embodiments of the disclosure, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, which are described below. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. The disclosure includes any alterations and further modifications in the illustrated devices and described methods and further applications of the principles of the disclosure, which would normally occur to one skilled in the art to which the disclosure relates. Moreover, the embodiments were selected for description to enable one of ordinary skill in the art to practice the invention.
Engine 10 further includes an intake system, indicated by numeral 14. Intake system 14 delivers the intake air into each of the cylinders in a known manner. In the depicted embodiments, intake system 14 comprises a fresh air inlet 16. Fresh air inlet 16 conveys ambient air to a compressor 18C of a turbocharger 18. After compressor 18C has compressed the fresh air, a charge air cooler, also known as an intercooler, 20 cools the fresh air before the air passes to an intake manifold 22. In a known manner, air enters a respective cylinder 12 when a respective intake valve or valves of the cylinder 12 is open.
In the depicted embodiment, engine 10 includes an exhaust gas recirculation (EGR) system, indicated by numeral 24, and an exhaust system, generally indicated by numeral 26. EGR 24 provides controlled recirculation of engine exhaust gases from exhaust system 26 of engine 10 to intake system 14 for purposes of emission control.
Exhaust system 26 comprises an exhaust manifold 28 and a turbine 18T of turbocharger 18. Exhaust manifold 28 may be any suitable manifold known in the art. Exhaust system 26 may also include one or more exhaust treatment devices (not shown) such as a diesel particulate filter (DPF) for trapping soot present within the exhaust air in order to prevent the trapped soot from escaping to the surrounding atmosphere, for example.
In the depicted embodiment, EGR system 24 comprises an EGR cooler package, generally indicated by numeral 30, an EGR intercooler 32 and an EGR valve 34. EGR cooler package 30 includes a housing 31, a first portion 40, a second portion 42, a divider wall 44, and a control valve 45. Housing 31 includes an inlet 30i and an outlet 30o. As shown, inlet 30i is in flow communication with first portion 40. Inlet 30i is also in flow communication with a flow path 43 to second portion 42. Flow path 43 is bounded by first portion 40, housing 31 and divider wall 44. The outlet side of first portion 40 is in flow communication with flow path 47, which is bounded by divider wall 44, second portion 42 and housing 31. Flow path 47 and the outlet side of second cooler 42 are in flow communication with outlet 30o of EGR cooler package 30. As indicated above, EGR cooler package 30 may be cooled in any suitable manner, such as jacket water cooling, for example. First portion 40 and second portion 42 of EGR cooler package 30 are each generally configured to cool the air passing through cooler package 30.
In the depicted embodiment, control valve 45 controls the manner in which air flows through cooler package 30. For example, when control valve 45 is in a closed position as depicted in dotted lines and indicated by numeral 45c, all of the air entering package 30 flows through first portion 40 prior to exiting the cooler package 30. None of the air (or at least substantially none of the air) flows through second package 42. Conversely, when control valve 45 is in an opened position as depicted in solid lines and indicated by numeral 45o, a portion of the air flowing through package 30 travels through first portion 40 and the remainder of the air travels through second portion 42 in parallel prior to exiting the cooler package 30. It should be understood that control valve 45 may be configured for controllable positioning in a plurality of positions intermediate the closed position 45c and the opened position 45c referenced above.
EGR charge air cooler, or EGR intercooler, 32, may also be utilized to further cool the air. EGR intercooler 32 may be any type of suitable intercooler, such as an air-cooled, or direct, intercooler, for example. It should be noted that in an alternate embodiment, EGR intercooler 32 may be omitted from engine 10.
Intercooler 32 includes an inlet 32i and an outlet 32o, and valve 34 includes an inlet 34i and outlets 34o and 34o′. In the depicted embodiment, inlet 30i conveys air from exhaust manifold 28 to cooler package 30. Air exiting cooler package 30 travels through outlet 30o and is then conveyed to valve 34 by way of inlet 34i. Air exiting valve 34 may travel from outlet 34o to inlet 32i and then enters intercooler 32. In addition, air exiting valve 34 may travel from outlet 34o′ to join with the air traveling though outlet 32o at junction 35. Outlet 32o conveys air from intercooler 32 to junction 35, and air travels through outlet 35o from junction 35 to intake 14.
It should be noted that in the depicted embodiment, valve 34 controls the flow of air through the EGR system 24. Specifically, valve 34 may direct air into outlet 34o and consequently into intercooler 32, or valve 34 may direct air into outlet 34o′ in order to allow the air to bypass intercooler 32. Furthermore, valve 34 may be fully closed thereby preventing air from flowing through inlet 30i and consequently, preventing air from traveling through cooler package 30. Accordingly, air from exhaust manifold 28 will be communicated to inlet 30i whenever valve 34 is at least partially open. Thus, whenever valve 34 is at least partially open, the air flows through EGR system 24 and into intake 14.
It should be noted that in embodiments of the invention, valve 34 may be replaced with a plurality of valves capable of collectively performing the same function. For example, valve 34 may be replaced with a first valve capable of selectively preventing the flow of air through cooler package 30, and a second valve capable of directing air from input 34i into either output 34o or output 34o′. Moreover, these valves may be placed in any number of suitable positions within the EGR system 24.
In operation, whenever valve 34 is opened and directs air into at least one of output 34o or output 34o′ thereby allowing air to flow through the EGR system 24, cooler package 30 may be in at least one of two different configurations. For example, at low power and low flow, wherein less cooling is necessary, valve 45 may be closed so that air only flows through first portion 40. First portion 40 is configured to ensure the air remains in turbulent flow in order to reduce the amount of soot deposited on first portion 40. When the engine is at a high flow and high power condition, valve 44 may be opened in order to allow the air flowing through the cooler package 30 to flow in parallel through both first portion 40 and second portion 42, i.e. such that a portion of the air flowing through package 30 travels through the first portion 40 and a portion of the air travels through second portion 42. In high power/high pressure conditions, the air flowing through cooler package 30 remains in a turbulent flow state in order to minimize the soot deposited on the portions 40, 42 of the cooler package 30.
In either instance, once the air exits from cooler package 30 by way of outlet 30o, the air passes into valve 34 by way of inlet 34i. Valve 34 may be configured to direct the air into outlet 34o and into intercooler 32 by way of inlet 32i. The passage of the air through intercooler 32 allows the temperature of the air to be lowered prior to the air being conveyed to intake 14 via outlet 32o.
It should be noted that in certain instances, valve 34 may be switched so that the air bypasses intercooler 32. For example, when intercooler 32 is air cooled and the ambient air is below freezing, valve 34 may be switched so that the air bypasses intercooler 32 in order to prevent the condensation of the moisture within the air.
In alternative embodiments, intercooler 32 may be removed from the engine 10, thereby allowing air to pass from cooler package 30 through valve 34 and into intake 14. In embodiments in which intercooler 32 is not present, valve 34 may be located at any suitable position within the EGR system 24.
It should be noted that the valves 34, 45 may be controlled in any suitable manner. For example, an engine control unit (not shown) may be used to control the degree to which the valves 34, 45 are opened. The engine control unit may also include a sensor configured to sense the power output and flow of the engine, in order to ensure the valves 34, 45 are opened appropriately and proper turbulent air flow is maintained through the cooler package 30 in order to minimize the deposit of soot.
Valve 144 may also be configured to direct a portion of the gas passing through the valve 144 into second cooler 142. Generally, when valve 144 directs a portion of the gas to second cooler 142, valve 144 continues to direct a portion of the gas to the first cooler 140. In the depicted embodiment of cooling package 130, the gas flowing through first cooler 140 and second cooler 142 recombines at junction 141 in a suitable manner. The recombined gas may then exit cooling package 130 via outlet 130o. It should be noted that in embodiments of the invention, first cooler 140 and second cooler 142 may be liquid cooled.
Referring now to
Control valve 160 is depicted in this embodiment as a flapper valve, with a movable portion 166 coupled to a pivotal connection 168 that is mounted to housing 152. Movable portion 166 is configured to obstruct, when valve 160 is in the closed position shown in solid lines in
In operation, under low load conditions (i.e., when the EGR flow rate is low), control valve 160 is in the closed position to inhibit flow through second portion 156 and provide a relatively smaller flow area (i.e., the cross-sectional area of first portion 154). This smaller flow area ensures sufficiently turbulent flow to reduce the amount of soot deposited (i.e., fouling) on first portion 154. Under high load conditions (i.e., when the EGR flow rate is high), control valve 160 is in the opened position to permit flow through second portion 156 in parallel with the flow through first portion 154, thereby providing a relatively larger flow area (i.e., the sum of the cross-sectional areas of first portion 154 and second portion 156). In this manner, the level of turbulence is maintained within an acceptable range to prevent a large pressure drop through cooler package 150.
It should be understood that by facilitating a variable cooler cross-section using control valve 160 in the manner described above, cooler package 150 can be controlled to maintain a Reynolds number in the turbulent flow range under low flow conditions without experiencing the undesirable effects of very high Reynolds numbers under high flow conditions. Moreover, it should be understood that the compact design of a U-shaped cooler package may reduce the space needed to receive the package, and may permit alternate mounting orientations such as vertical instead of horizontal.
While these embodiments have been described as having exemplary designs they may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosed general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this application pertains.
This application is a continuation-in-part of patent application Ser. No. 11/933,603, filed Nov. 1, 2007, the subject matter of which are hereby expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11933603 | Nov 2007 | US |
| Child | 12260632 | US |
