Patent Application
20120227400
Two-stage turbo charging systems, such as for use with internal combustion engines, are well-known in the art. Two-stage turbocharger includes a high pressure turbocharger and a low pressure turbocharger. The high pressure turbocharger (high pressure stage) includes a high pressure turbine coupled to a compressor. Similarly, the low pressure turbocharger includes a low pressure turbine coupled to a compressor. The turbine operates by receiving exhaust gas from an internal combustion engine and converting a portion of the energy in that exhaust gas stream into mechanical energy by passing the exhaust stream over blades of a turbine wheel, and thereby causing the turbine wheel to rotate. This rotational force is then utilized by the compressor, coupled by a shaft to the turbine wheel, to compress a quantity of air to a pressure higher than the surrounding atmosphere. This provides an increased amount of air available to be drawn into the internal combustion engine cylinders during the engine's intake stroke. The additional compressed air taken into the cylinders may allow more fuel to be burned within the cylinder, and thereby offers the opportunity to increase the engine's power output.
In certain situations, such as to meet the air flow requirements at part load, it is required to switch between the two turbo charging stages through use of a bypass system to divert exhaust gas flow around the higher pressure turbocharger to the lower pressure turbocharger. The by-pass flow is generally known as bleed flow. Generally, the bleed flows on the bypass system are simply injected into the lower pressure turbine in a manner that is convenient from the packaging perspective. However, in such situations bleed flows are injected in a manner which affects the efficiency of the high pressure turbine and the lower pressure turbine. Additionally depending on the turbocharger arrangement the diffuser downstream of the high pressure turbocharger may need to have a very steep angle and/or in some cases large bends, decreasing the efficiency of both the low pressure and the high pressure turbocharger.
For these and other reasons, there is a need for embodiments of the invention
A turbine system for a multistage turbocharger and a method for utilizing the same are disclosed. The turbine system includes a high pressure turbine having an inlet for receiving a flow of fluid, and an outlet for passing the flow on extraction of work from the high pressure turbine. A low pressure turbine, downstream of the high pressure turbine, having an inlet for receiving a flow of fluid from downstream of the high pressure turbine. A diffuser connecting the outlet of the high pressure turbine and the inlet of the low pressure turbine. A bypass for bypassing a portion of the flow around the high pressure turbine, from upstream of the high pressure turbine to downstream of the high pressure turbine. An injector to input the bypass flow in the diffuser in a manner to reduce flow separation in the diffuser.
Embodiments of the present invention provide an improved turbine system for a multistage turbocharger and an internal combustion engine system utilizing the improved turbine system. Embodiments of the present invention further provide a method of increasing efficiency of a multistage turbocharger in an internal combustion engine.
In an embodiment of the present invention, the intake air entering in the internal combustion engine 100 may be optionally mixed with recirculated exhaust gases (EGR) to form a charge-air mixture. The intake air or EGR/intake air mixture (“charge-air”) flows through and is compressed by a low pressure air compressor 114. The low pressure air compressor 114 may be a centrifugal compressor. After compression in the low pressure air compressor 114, the intake air may flow through a high pressure air compressor 116 for further compression. The high pressure air compressor 116 may also be a centrifugal compressor. In an embodiment of the present invention, the intake air may be diverted before it flows through the high pressure air compressor 116 and is fed directly into the intake manifold 106. The internal combustion engine system 100 may optionally also include an inter stage cooler (not illustrated), between the low pressure air compressor 114 and the high pressure air compressor 116 and after cooler (not illustrated) between the high pressure air compressor 116 and the intake manifold 106.
Subsequently, the intake air enters the intake manifold 106 and into the combustion chambers 104 of the internal combustion engine system 100. Following, combustion in the combustion chambers 104 of the internal combustion engine 100, the warm, pressurized exhaust gases leave the combustion chambers 104 at a higher exhaust gas energy level and flow through the exhaust manifold 108 to the exhaust line 112.
These pressurized exhaust gases coming from the exhaust manifold 108 are utilized by the multistage turbocharger 102. The multistage turbocharger 102 includes a turbine system 118. The multistage turbocharger 102 has two stages of turbocharging namely a high pressure turbocharger and a low pressure turbocharger. A high pressure turbine 120 in exhaust line 112 is coupled to the high pressure air compressor 116 in the intake line 110 through a first shaft 122, and together the combined turbine and compressor device forms the high pressure turbocharger. Similarly, a low pressure turbine 124 in the exhaust line 112 is coupled to the low pressure air compressor 114 in intake line 110 through a second shaft 126, and together the turbine and compressor form the low pressure turbocharger.
The turbine system 118 further includes a diffuser 128 downstream of the high pressure turbine 120. The diffuser 128 connects an outlet of the high pressure turbine 120 and an inlet 130 of the low pressure turbine 124. The exhaust gases, on extraction of work, through the high pressure turbocharger flows through the diffuser 128 into the inlet 130 of the low pressure turbine 124. Herein it may be apparent to those skilled in that art that a conventional diffuser, such as the diffuser 128 may be an elongated section, for example. However, other configurations may be possible. The diffuser 128 conventionally, conserves the energy of the exhaust fluid and converts a portion if its kinetic energy into pressure, as the fluid flows through the diffuser 128.
Referring again to
Alternatively, depending on the various load conditions it may required to divert a portion of the exhaust gases upstream of the high pressure turbine 120 to downstream of the high pressure turbine 120. Thus, the turbine system 118 further includes a bypass channel 136 to divert a portion of the exhaust gases from upstream of the high pressure turbine 120. The bypass channel 136 extends from the exhaust line 112, from upstream of the high pressure turbine 120, to connect with the diffuser 128, downstream of the high pressure turbine 120. Specifically, a first end portion 138 of the bypass channel 136 is connected to the exhaust line 112 and a second end portion 140 of the bypass channel 136 is connected to the diffuser 128. Further, the bypass channel 136 may include a control valve 142 that, depending upon the load conditions regulates the portion of the exhaust gases that must be diverted from upstream of the high pressure turbine 120. The control valve 142, in an open condition thereof, directs a portion of the exhaust gases coming from the exhaust line 112 through the bypass channel 136, thereby precluding the entire exhaust gases from entering the high pressure turbine 120.
The exhaust gases circulated out from the outlet 134 of the high pressure turbine 120 and the bypassed exhaust gases mix inside the diffuser 128 before the exhaust gases enters the low pressure turbine 124. The flow coming from the high pressure turbine 120 and/or from the bypass channel 136 may be turbulent. In such cases, diffuser 128 may experience boundary layer formation, flow separation and thus experience losses, such as but not limited to, pressure loss etc. Such losses may substantially hamper the performance of the turbines. In an embodiment of the present invention, the bypass channel 136 further includes an injector 144 to inject the bypass flow into the diffuser 128. The injector 144 inputs the bypassed flow in the diffuser 128 in a manner to reduce flow separation in the diffuser 128.
The injector 144 is designed such that the injection of the bypassed flow in the diffuser 128 reduces the flow separation in the diffuser 128. Moreover, the reduced flow separation in the diffuser 128 may enable the assembly of the high pressure turbine 120 and the low pressure turbine 124 closer together. Thus, the diffuser 128 may be relatively short in length. Alternatively, the diffuser 128 may be designed with more aggressive bends, and thus occupy less space. Advantageously, the assembly of the high pressure turbine 120 and the low pressure turbine 124 closer together may enable a more compact packing of the internal combustion engine 100.
The various embodiments explained herein are non-limiting exemplary embodiments and there can be other methods and configurations employed as the injector to reduce flow separation in the diffuser.
The intake air enters the intake manifold 106 and into combustion chambers 104 of the internal combustion engine system 100. Following, combustion in combustion chambers 104 of the internal combustion engine 100, the warm, pressurized exhaust gases leave the combustion chambers 104 at a higher exhaust gas energy level and flow through the exhaust manifold 108 to the exhaust line 112.
At step 402, pressurized exhaust gases coming from the exhaust manifold 108 are passed through the multistage turbocharger 102. The multistage turbocharger 102 has two stages of turbocharging namely the high pressure turbocharger and the low pressure turbocharger. The high pressure turbine 120 in exhaust line 112 is coupled to the high pressure air compressor 116 in the intake line 110 through the first shaft 122, and together the combined turbine and compressor device forms the high pressure turbocharger. Similarly, the low pressure turbine 124 in exhaust line 112 is coupled to the low pressure air compressor 114 in the intake line 110 through the second shaft 126, and together the turbine and compressor form the low pressure turbocharger.
The turbine system 118 further includes the diffuser 128, downstream of the high pressure turbine 120 that connects the outlet 134 of the high pressure turbine 120 and the inlet 130 of the low pressure turbine 124. The exhaust gases, after extraction of work, through the high pressure turbocharger flows through the diffuser 128 into the inlet 130 of the low pressure turbine 124.
After leaving the exhaust manifold 108, exhaust gases in exhaust line 112 may flow through the inlet 132, which is fluidly connected with the exhaust line 112, of the high pressure turbine 120. During the passage of the exhaust gas through the high pressure turbine 120, extraction of work from the fluid is done by means of the high pressure air compressor 116 and the exhaust gas is circulated out through the outlet 134 of the high pressure turbine 120 into the diffuser 128 connecting the high pressure turbine 120 and the low pressure turbine 124. Subsequently, the inlet 130 of the low pressure turbine 124, positioned on a downstream of the high pressure turbine 120, receives the flow of the exhaust gases from the diffuser 128. Thus, the exhaust gases may further expand in the low pressure turbine 124 before the exhaust gases are circulated out of the internal combustion engine 100 through the outlet 146.
Alternatively, at step 404, depending on the various load conditions, a portion of the exhaust gas is bypassed from an upstream of the high pressure turbine 120. The turbine system includes the bypass channel 136 to divert a portion of the exhaust gases upstream of the high pressure turbine 120. The bypass channel 136 extends from the exhaust line 112, from upstream of the high pressure turbine 120, to connect with the diffuser 128, downstream of the high pressure turbine 120. Further, the bypass channel 136 includes the control valve 142 that regulates, depending upon the load conditions, the portion of the exhaust gases that must be diverted from upstream of the high pressure turbine 120. The control valve 142, in an open condition thereof, directs a portion of the exhaust gases coming from the exhaust line 112 through the bypass channel 136, thereby precluding the entire exhaust gases from entering the high pressure turbine 120.
The exhaust gases circulated out from the outlet 134 of the high pressure turbine 120 and the bypass flow mix inside the diffuser 128 before the exhaust gases enters the low pressure turbine 124. The flow coming from the high pressure turbine 120 and/or the bypass channel 136 may be turbulent. In such cases, the diffuser 128 may experience boundary layer formation, flow separation and thus experience losses, such as but not limited to, pressure loss etc. Such losses may substantially hamper the performance of the turbines. In an embodiment of the present invention, the bypass channel 136 further includes the injector 144 for injecting the bypass flow into the diffuser 128.
At step 406, the injector 144 inputs the bypass flow in the diffuser 128 in a manner to reduce flow separation in the diffuser 128. The injector 144 is designed such that the injection of the bypass flow in the diffuser 128 reduces the flow separation in the diffuser 128. Thus, the losses occurring in the fluid during its passage through the diffuser 128 get reduced. Moreover, the reduced flow separation in the diffuser 128 may enable the assembly of the high pressure stage and the low pressure stage closer together. Thus, the diffuser 128 may be relatively short in length. Alternatively, the diffuser 128 may have a ninety degree bent and thus occupy less space. Advantageously, the assembly of the high pressure stage and the low pressure stage closer together may enable a more compact packing of the internal combustion engine 100. In an embodiment of the present invention, the bypass flow is injected at an angle to at least one surface wall 204 of the diffuser 128. The bypass flow on injected in the diffuser 128 may push the flow received from the high pressure turbine 120 towards the inlet 130 of the low pressure turbine 124. In another embodiment of the present invention, the bypass flow is injected at a swirl angle to the flow received from the high pressure turbine 120. In yet another embodiment, the bypass flow is injected towards the center of a longitudinal axis of the diffuser 128. It may be apparent to those skilled in the art that due to the formation of the boundary layer, the flow velocity at the internal boundary of the diffuser 128 tends to be less. However, the injector 144 of the present invention is designed in such a manner that the injected flow may re-energizes the flow from the high pressure turbine 120, which reduces the formation of the boundary layer, and thus minimizes the pressure losses. Further, the injected bypass flow may also allow having a much steeper/higher angle at the connection between the high pressure turbine 120 and the low pressure turbine 124 and thus leads to compact design and packing advantages.
The present invention has been described in terms of several embodiments solely for the purpose of illustration. Persons skilled in the art will recognize from this description that the invention is not limited to the embodiments described, but may be practiced with modifications and alterations limited only by the spirit and scope of the appended claims.
