Patent Application
20160186634
The present disclosure generally relates to after-treatment systems for internal combustion engines. More particularly, the present disclosure relates to thermal management of after-treatment systems for internal combustion engines using a turbocharger.
Internal combustion engines have been known to employ turbochargers to improve a volumetric efficiency of the engine. In addition, after-treatment systems may be provided downstream of the turbochargers to reduce emissions for e.g., CO, NOx, and/or Particulate matter (PM).
As such, a typical exhaust after-treatment system requires that the temperature of the exhaust stream downstream of the turbocharger be maintained at an elevated value for ensuring efficient functioning of components in the after-treatment system. Such components may include a Diesel Oxidation Catalyst (DOC), and/or a Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), Lean NOx Trap (LNT) provided downstream of the turbocharger.
U.S. Patent Publication No. 2012/0017587 discloses an engine exhaust after-treatment system using a turbocharger. The turbocharger utilizes exhaust stream to drive a turbine coupled to a compressor and for compressing inlet air. The exhaust after-treatment system also includes a bypass passage allowing flow of exhaust stream therethrough while bypassing the turbocharger. A hydrocarbon injector injects diesel fuel in the exhaust stream upstream of the turbocharger. However, the diesel fuel, being in liquid state, may hamper operation of turbocharger due, at least in part, by allowing the diesel fuel to interfere with the turbine blades of turbocharger. Such injection of the diesel fuel may therefore, deteriorate a performance of the turbocharger.
J. P. Patent Publication No. 2014058927 discloses an engine exhaust after-treatment system employing a turbocharger to boost volumetric efficiency of the engine. The turbocharger is configured to receive a flow of exhaust gases exiting the combustion chamber and utilize thermal energy from the exhaust gases to drive a compressor used to compress inlet gases. An exhaust bypass passage is provided in the exhaust after-treatment system; the exhaust bypass passage being configured to bypass the turbocharger. A hydrocarbon injector injects diesel fuel downstream of the turbocharger. However, the diesel fuel, being in liquid state, may take up thermal energy from the exhaust stream exiting the turbocharger. The exhaust stream exiting the turbocharger may therefore, lose a significant amount of thermal energy in the turbocharger and liquid fuel injection downstream of the turbocharger causing a drop in temperature of the exhaust after-treatment system and deteriorating a conversion efficiency of the exhaust after-treatment system.
Hence, there is a need for an exhaust after-treatment system which overcomes the aforementioned drawbacks associated with locating the hydrocarbon injector upstream or downstream of the turbocharger.
In an aspect of this disclosure, an exhaust after-treatment system for an internal combustion engine includes an exhaust passage disposed in fluid communication with an exhaust manifold of the engine. The exhaust passage is configured to receive a stream of exhaust gases exiting the exhaust manifold. A turbocharger is fluidly coupled to the exhaust passage. The turbocharger is located downstream of the combustion chamber and is configured to be operatively driven by a first portion of the exhaust gases exiting the exhaust manifold. A bypass line is disposed parallel to the turbocharger. Moreover, the bypass line is fluidly coupled to the exhaust passage upstream and downstream of the turbocharger. The bypass line is configured to receive a second portion of the exhaust gases exiting the combustion chamber. A fuel injector is disposed in the bypass line. The fuel injector is configured to inject a pre-determined amount of fuel in the second portion of the exhaust gases. An exhaust after-treatment module is disposed in the exhaust passage and located downstream of the bypass line. The exhaust after-treatment module is configured to treat the mixture of the first portion and the second portion of the exhaust gas.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts. Moreover, references to various elements described herein are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice-versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claims.
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The engine system 100 further includes a bypass line 132 to the exhaust passage 116 located parallel to the turbocharger 120 and coupled to both upstream as well as downstream of the turbocharger 120. The bypass line 132 includes a bypass control element 134 that may be operated to adjust the flow of exhaust gas 106 so that a second portion of exhaust gases 124 is being received in the bypass line 132. By adjusting the flow of exhaust gas 106 in ratio of first portion of exhaust gas 122 and second portion of exhaust gas 124, the amount of energy extracted from exhaust flow through the turbine 126 may be varied. For example, the bypass control element 134 is operably coupled with the bypass line 132 such that a position of the bypass control element 134 governs an extent to which the bypass line 132 is open for passage of fluid such as exhaust gas 106. The bypass control element 134 may be opened, for example, to divert the second portion of exhaust gas 124 away from the turbine 126, and into the bypass line 132. Accordingly, the rotating speed of the compressor 128, and thus the boost provided by the turbocharger 120 to the engine 102 may be regulated. Consequently, the amount of energy extracted by the turbocharger 120 from exhaust flow through the turbine 126 is also adjusted. The bypass control element 134 may be any element that may be selectively controlled to partially or completely block a passage. As an example, the bypass control element 134 may be a gate valve, a butterfly valve, a globe valve, an adjustable flap, or the like.
In an alternative embodiment, the engine cylinders may be divided into two compartments or portions, where exhaust gas from one set of cylinders flows through the turbine 120 and exhaust gas from the second set controllably flows through the turbine 120 based on a position of the bypass control element 134.
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The DOC 140 uses a chemical process to reduce hydrocarbons and carbon monoxide (CO) in the exhaust stream 146. The DOC 140 reacts with the hydrocarbons and oxidizes them into less harmful components such as Carbon Dioxide (CO2) and water vapor in the presence of a catalyst. The DPF 142 traps particulate matter that is carried in the exhaust stream 146, preventing the particulate matter from being released into the atmosphere. Inside the DPF 142, particulate matter, sometimes referred to as “soot,” is trapped until it is oxidized during a regeneration process.
In an embodiment, a particulate load of the DPF 142 may exceed a threshold load, and the engine system 100 may enter the regeneration mode of operation, which is illustrated in detail in
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Generally, a particulate load of the DPF 142 may increase such that regeneration of the DPF 142 needs to be carried out to clean the DPF 142 so that a backpressure on the engine 102 does not increase beyond an allowed level. Further, the DPF 142 is positioned downstream of the turbine 126 of the turbocharger 120 in the exhaust passage 146, an exhaust gas temperature upstream of the DPF 142 and downstream of the turbine 120 may not be high enough to passively regenerate the DPF 142. The fuel injector 150 located in the bypass line 132 may selectively inject a predetermined amount of fuel into a portion of exhaust gas 124 that is being routed through the bypass line 132. This increases the temperature of exhaust gases 146, entering the exhaust after-treatment module 104 to an effective temperature that is required to carry out the regeneration of the DPF 142.
The engine system 100 also includes a controller 152 operatively connected to various components of the engine system 100. The controller 152 is programmed to predict a threshold value for the mass of soot which collects in the exhaust after-treatment module 104 during operation of the engine 102. The threshold value for the mass of soot is the maximum amount of soot that is allowed to be reached or collected in the exhaust after-treatment module 104 before regeneration of the exhaust after-treatment module 104 is performed. In an embodiment, the threshold value may be established as a function of an operating speed of engine 102 and a quantity of fuel that has entered the engine 102 for combustion. Speed of engine 102 may be sensed by an engine speed sensor 154, while the amount of fuel that has entered the engine 102 may be sensed by a fuel sensor 156. The threshold value of soot may be an amount of soot that has been empirically determined to be the level at which regeneration of exhaust after-treatment module 104 should be performed. Based on the inputs from the engine speed and fuel sensors 154 and 156, and the threshold value of mass of soot, the controller 152 determines a requirement for the regeneration of the exhaust after-treatment module 104.
Further, once the controller 152 determines to perform regeneration of the exhaust after-treatment module 104, the controller 152 is also programmed to monitor exhaust gas temperature T via the sensor module 148. A minimum value of exhaust temperature required to perform regeneration T0 may be stored in the controller 152. The controller 152 compares the exhaust temperature T measured by the sensor module 148 to the minimum value T0. If the exhaust temperature T is greater than or equal to T0, the controller 152 performs the regeneration of exhaust after-treatment module 104. However, if the exhaust temperature T is less than T0, the controller 152 may not perform the regeneration of exhaust after-treatment module 104 without elevating the exhaust temperature T up to at least T0.
To elevate the exhaust temperature T up to T0, the controller 152 commands the fuel injector 150 in the bypass line 132 to inject fuel in the second portion of exhaust stream 124. The amount of fuel to be injected by the fuel injector 150 may be calculated based on a difference in exhaust temperature T and T0 denoted as dT. Alternatively, a lookup table may be stored in controller 152 memory. The lookup table may have an amount of fuel to be injected in bypass line 132 mapped to the exhaust gas temperature T.
After injecting the fuel in the bypass line 132, the controller 152 again calculates dT to check whether the temperature T has been elevated to T0. Once the temperature T is greater than or equal to T0. the controller 152 performs regeneration of the exhaust after-treatment module 104. In case, the temperature T is still less than the temperature T0, the controller 152 repeats the process of injecting fuel in the bypass line 132 via the fuel injector 150.
Although the above example is explained to determine when the regeneration of the DPF 142 needs to be carried out, it should not limit the scope of the present disclosure, and any process known in the art can be utilized to determine the requirement of regeneration for the DPF 142.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
