Turbocharger having cooling arrangement for compressor and method thereof

A method of cooling a compressor, providing compressed working fluid, in a natural gas based combustion engine is provided. The method includes diverting at least a portion of natural gas from a fuel tank of the combustion engine. The method further includes routing the portion of natural gas towards the compressor. The method also includes providing one or more nozzles disposed at one or more strategic locations of the compressor. The method further includes injecting the portion of natural gas, via the one or more nozzles, inside the compressor. The method also includes allowing the portion of natural gas to diffuse with the compressed working fluid inside the compressor in an endothermic expansion process, to convectively cool the compressor.

TECHNICAL FIELD

The present disclosure relates to a turbocharger for a natural gas based combustion engine, and more particularly, to a method of cooling a compressor in a turbocharger of a natural gas based combustion engine.

BACKGROUND

In order to maximize power generated by an internal combustion engine, sometimes the engine may be equipped with a turbocharger. Typically, the turbocharger includes a compressor that compresses the air flowing into the engine. As the intake air is compressed by the compressor, the temperature of compressor body and its components, such as compressor wheel, may rise significantly. The materials used to construct the compressor are selected by consideration of cost and operating parameters. Traditionally, materials, including titanium alloys and the like, that can withstand higher operating temperatures are used to construct compressor components. However, such materials are relatively expensive, and usually are also difficult to machine. While an aluminum alloy based compressor is relatively cost beneficial and responds faster due to light weight and low inertia, it may be unsuitable for applications in which the compressed air temperature is or is expected to rise above a threshold value during operation.

U.S. Pat. No. 7,021,058, hereinafter referred to as the '058 patent, relates to a supercharging air compressor for an internal combustion engine, having a compressor wheel which is rotatably mounted in a compressor inlet duct, and to which combustion air can be fed via the compressor inlet duct. A partial stream of the compressed supercharging air is branched off downstream of the compressor wheel and is fed to a temperature reducing unit. The branched-off partial stream is fed, as cooling air, to a component of the supercharging air compressor after it has flowed through the temperature reducing unit. The proposed arrangement in the '058 patent may be able to cool the air compressor, however such an application requires employing a separate temperature reducing unit. This separate unit may add to the overall cost of the turbocharger assembly and may further need to withdraw power from the engine, which in turn, affects the engine's efficiency.

SUMMARY

In one aspect of the present disclosure, a method of cooling a compressor, providing compressed working fluid, in a natural gas based combustion engine is described. The method includes diverting at least a portion of natural gas from a fuel tank of the combustion engine. The method further includes routing the portion of natural gas towards the compressor. The method also includes providing one or more nozzles disposed at one or more strategic locations of the compressor. The method further includes injecting the portion of natural gas, via the one or more nozzles, inside the compressor. The method also includes allowing the portion of natural gas to diffuse with the compressed working fluid inside the compressor in an endothermic expansion process, to convectively cool the compressor.

In another aspect of the present disclosure, a turbocharger for a natural gas based combustion engine is described. The turbocharger includes a turbine, and a compressor associated with the turbine. The compressor is configured to provide a compressed working fluid to the combustion engine. The turbocharger also includes a fluid conduit connecting the compressor to a fuel tank of the combustion engine. The fluid conduit is configured to supply at least a portion of natural gas from the fuel tank to the compressor. The turbocharger further includes one or more nozzles operatively coupled with the compressor. The one or more nozzles are configured to inject the portion of natural gas inside the compressor.

In yet another aspect of the present disclosure, a method of assembling a turbocharger for a natural gas based combustion engine is described. The method includes providing a center housing. The method further includes installing a compressor onto the center housing. The method also includes providing a fluid conduit to connect the compressor to a fuel tank of the combustion engine. The fluid conduit is configured to supply at least a portion of natural gas from the fuel tank to the compressor. The method further includes installing one or more nozzles at one or more strategic locations of the compressor. The one or more nozzles are configured to inject the portion of natural gas inside the compressor.

DETAILED DESCRIPTION

Reference will now be made in detail to specific aspects or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts.

FIG. 1illustrates a block diagram for an engine100, in accordance with an embodiment of the present disclosure. The engine100may find applications in machines (not shown) such as, but not limited to, mining trucks, excavators, wheel loaders, or any heavy engineering machines, and furthermore in some stationary machines, such as generator or pump. The engine100may include a crankcase102that forms a plurality of cylinders104. Although inFIG. 1, six cylinders104are shown in an inline arrangement, fewer or more cylinders arranged in a different configuration within the crankcase102, for example in a V-configuration, may be used. Although not shown here, each cylinder104may include a reciprocating piston connected to a common crankshaft. It may be contemplated that in the engine100, the combustion of a fuel and air mixture in the cylinders104generates motive power for the machine, and a resultant mixture of exhaust gas is produced in the known fashion.

The engine100may include an intake manifold106, which is selectively in fluid communication with each cylinder104and provides compressed intake air to the cylinders104. The engine100may include a fuel tank108to store suitable fuel for the engine100. In an embodiment, the engine100may be a natural gas based combustion engine. Hereinafter, the terms “natural gas based combustion engine,” “combustion engine” and “engine” have been interchangeably used without any limitations. The fuel tank108may be designed to store the natural gas in either a liquid form, such as Liquefied Natural Gas (LNG); or gaseous form, such as Compressed Natural Gas (CNG); or alternatively both forms at different times, for carrying combustion process in the engine100. The fuel tank108may be connected to the cylinders104of the engine100via a supply line110, for supply of the natural gas to the engine100. In some examples, the engine100may include a vaporizer (not shown) to first convert the LNG into gaseous form before being supplied to the engine100. The engine100may include multiple fuel injectors112associated with each of the cylinders104and disposed in fluid communication with the fuel tank108through the supply line110to receive the natural gas, and configured to inject the natural gas into the cylinders104. The compressed air along with the natural gas provided to the cylinder104forms a combustible mixture that ignites when compressed or in the presence of a spark. Combustion byproducts are evacuated from each cylinder104through exhaust valves114and exhaust runners116. The engine100may also include an exhaust manifold118, which collects the exhaust gas from each cylinder104. In the engine100, the intake air in the intake manifold106as well as the released exhaust gas in the exhaust manifold118, are under pressure. Hereinafter, the terms “intake air,” “ambient air,” “air” and “working fluid” have been interchangeably used without any limitations.

To provide the power used to compress the intake air, different engine applications may use one or more different devices. In an embodiment of the present disclosure, the engine100may include a turbocharger assembly120(also simply referred to as “turbocharger”) to provide the compressed air to the intake manifold106. As schematically illustrated inFIG. 1, the turbocharger assembly120may be fluidly connected to the exhaust manifold118and arranged to receive pressurized exhaust gas therefrom. Various types, sizes and numbers of turbochargers have been used with engines in the past. One design consideration when selecting an appropriate turbocharger for an engine application is the air flow rate and desired pressure ratio of engine intake air that is desired. It may be appreciated that the engine100may include more than one turbocharger assembly; for example, the engine100may implement staged compression of air utilizing two or more turbochargers. Moreover, one or more turbochargers may be replaced by a mechanically or electrically driven compressor or supercharger. Additionally, hybrid systems such as turbochargers with electrically, hydraulic or pneumatic assist mechanisms may be used.

FIGS. 2-3illustrate different views of the turbocharger assembly120, according to different perspectives. The turbocharger assembly120may, generally, include a turbine122and a compressor124. As illustrated, the turbine122and the compressor124may include a turbine housing126and a compressor housing128, respectively. Further, the turbine housing126and the compressor housing128may be connected to each other by a center housing130.FIG. 4illustrates an outline view of the turbocharger assembly120with the turbine housing126and the compressor housing128removed to reveal their inner components. As may be seen fromFIG. 4, the turbine122may include a turbine wheel131surrounded by the turbine housing126, and the compressor124may include a compressor wheel132surrounded by the compressor housing128. Both the turbine wheel131and the compressor wheel132may be connected to each other on opposite ends of a shaft133. The shaft133may extend through the center housing130in the known fashion.

It may be contemplated that the turbine122may include an inlet134fluidly connected to the exhaust manifold118, to receive exhaust gas during engine operation, where the exhaust gas operates to cause the turbine wheel131connected to the shaft133to rotate before exiting the turbine122through an outlet135. The exhaust gas exiting the turbine122of the turbocharger assembly120may optionally be provided to exhaust treatment devices and systems (not shown) that mechanically and chemically removes combustion byproducts from the exhaust gas stream, and/or a muffler that dampens engine noise, before the exhaust gas is released into the environment. Similarly, the compressor124may include an inlet136to receive ambient air from the atmosphere, and an outlet137to supply the compressed intake air to the intake manifold106of the engine100. It may be contemplated by a person skilled in the art that in the turbocharger assembly120, the exhaust gas passes through a scrolled passage of the turbine122and impinges onto the turbine wheel131causing it to turn, rotating the shaft133, which in turn operates the compressor wheel132. The powered rotation of the compressor wheel132draws ambient air into the compressor housing128having a scrolled shape and compresses it. In some examples, the compressor124may include additional components, such as a fan (not shown) or the like, which aids with pulling the ambient air into the compressor124.

When the compressor124is assembled, a back-plate138extends around the shaft133and is connected to the center housing130such that the compressor wheel132and the center housing130are on opposite sides of the back-plate138. The back-plate138may be connected to the compressor housing128through fasteners, such as nut and bolts. The compressor housing128along with the back-plate138may enclose the compressor wheel132, and define an interior space therebetween. The compressor housing128may also define an exducer section139proximal to where the compressed working fluid exits from the compressor wheel132. It may be contemplated that the turbine122may also have a somewhat similar arrangement as that of the compressor124, which is not described in detail herein for the brevity of the disclosure. Further, the center housing130may also include other structures, such as bearings, which are lubricated and which limit axial motion of the shaft133along its centerline due to thrust loadings on the turbine wheel131and the compressor wheel132during operation. In some examples, the center housing130may include an internal gallery (not shown) through which oil is provided via an oil supply opening, which may later be drained back to the crankcase102of the engine100.

Referring toFIGS. 1-4in combination, the turbocharger assembly120of the present disclosure may further include a fluid conduit140to supply at least a portion of natural gas from the fuel tank108to the compressor124. In one example, the fluid conduit140may directly connect the compressor124of the turbocharger assembly120to the fuel tank108of the engine100(not shown in the drawings). In other example, as illustrated inFIG. 1, the turbocharger assembly120may include a diverter valve142which is a three-way valve disposed on the supply line110and further connected to the fluid conduit140from its one end, and configured to divert at least a portion of natural gas from the supply line110and route it towards the compressor124. The compressor124may also include one or more connections144formed at some strategic locations therein, to allow attachment of the other end of the fluid conduit140and thereby receive the supply of the portion of natural gas. In the illustrated embodiment ofFIGS. 2-4, only one connection144is shown, however it may be understood that the compressor124may include a plurality of connections144, as will be described later. As may be seen, the connection144may define an internal passageway146, with internal walls148, extending into the compressor housing128. In some examples, the fluid conduit140may include some custom fittings (not shown) formed at the other end to allow for attachment with the connections144, in the compressor124.

As previously described, the back-plate138may be connected to the center housing130and disposed adjacent to the compressor wheel132. As illustrated in the cross section ofFIG. 5, the compressor wheel132may include a generally conical hub150that supports a plurality of radially extending blades152. The hub150defines an inward-facing surface, referred to as base surface154, which faces the back-plate138. A radially extending cavity156is defined between the base surface154of the compressor wheel132and an inner surface158of the back-plate138. As shown inFIG. 5, the cavity156may extend peripherally around the shaft133and is substantially exposed to outer peripheral portions of the base surface154of the compressor wheel132. Further, the internal passageway146of the connection144may be fluidly open to the cavity156such that direct fluid communication is established between the fluid conduit140and the cavity156.

In accordance with an embodiment of the present disclosure, the turbocharger assembly120may include one or more nozzles160operatively coupled with the compressor124. The nozzles160may be sited in the internal walls148of the connections144, in the compressor124. The nozzles160may be disposed in fluid communication with the connections144to receive the portion of natural gas via the internal passageway146, and configured to inject the portion of natural gas inside the compressor124. The one or more nozzles160, and thereby the connections144, may be provided at some strategic locations in the compressor124, for the purpose of injecting the portion of natural gas. In one example, the strategic location to position the nozzle160is one or more of the back-plate138and the exducer section139, of the compressor124. In the illustrated embodiments, the nozzles160are disposed at connections144provided in the back-plate138pointing towards the outlet137of the compressor124, such that the portion of natural gas is injected in the exducer section139in a direction of flow of working fluid inside the compressor124. Further, in one example, the strategic location to position the nozzle160is proximal to the inlet136of the compressor124. In such example, the one or more nozzles160may be disposed proximal to the inlet136of the compressor124such that the portion of natural gas is injected in a direction of flow of working fluid into the compressor124. For this purpose, the inlet136may be considered to be the section of the compressor124which is substantially close to the upstream of the compressor wheel132. It may be understood that the connections144and the nozzles160may be designed to withstand high pressures of the CNG and/or low temperatures of the LNG, as the natural gas is supplied thereto.

FIG. 6illustrates a planar view of the compressor124from the side opposite to the back-plate138. As illustrated, the compressor124is shown to include multiple connections144arranged around the periphery of the compressor wheel132. In one embodiment, as representatively illustrated inFIG. 6, the nozzles160, in the compressor124, are arranged around the compressor wheel132in a ring shaped manner. That is, the nozzles160may be arranged along the radial periphery of the compressor wheel132at an outer diameter of the compressor housing128and/or the back-plate138. For this purpose, a disk (not shown) having a plurality of apertures formed at regular annular intervals therein and with the nozzles160arranged in such apertures may be employed, and the disk may be disposed within the cavity156. The ring shaped arrangement may direct the natural gas to impinge on targeted locations on the base surface154of the compressor wheel132that has been determined to be an area of high thermal stress, where such determination may be made empirically or numerically. Further,FIG. 7illustrates a section of a portion of the compressor124. In one embodiment, as illustrated therein, a plurality of discrete nozzles160may be disposed on one or both of the compressor housing128and the back-plate138to inject the portion of natural gas inside the interior space of the compressor housing128. It may be understood that the configuration of the nozzles160and other components may vary as shown in various figures, without any limitations.

FIG. 8illustrates a high-level schematic for a cooling arrangement, generally referenced by the numeral800, for cooling the compressor124, in the turbocharger assembly120. The cooling arrangement800may generally provide the fluid conduit140to connect the compressor124to be in fluid communication with the fuel tank108. The cooling arrangement800may also provide the diverter valve142to divert at least a portion of natural gas from the fuel tank108towards the compressor124. In some examples, the cooling arrangement800may include a controller (not shown) to control the diverter valve142, for regulating the supply of natural gas to the compressor124. The functioning of controller for regulating the fluid flow is well known in the art, and thus has not been described in detail herein. The cooling arrangement800may further provide one or more nozzles160disposed at one or more strategic locations in the compressor124. The cooling arrangement800may configure the nozzles160to inject the portion of natural gas into the compressor124. Usually, the natural gas is available for application either as CNG, which is typically 3600 psi; or as LNG, which is cryogenically stored at −160° C. The portion of natural gas when injected into the compressor124diffuse with the compressed working fluid inside the compressor124in an endothermic expansion process by Joule-Thomson effect, and thereby convectively cool the compressor124.

INDUSTRIAL APPLICABILITY

Internal combustion engines are supplied with a mixture of air and fuel for combustion within the engine that generates mechanical power. To maximize the power generated by the combustion process, the engine is often equipped with a turbocharger. The turbocharger utilizes exhaust gas from the engine to compress intake air flowing into the engine, thereby forcing more air into a combustion chamber of the engine than a naturally-aspirated engine could otherwise draw into the combustion chamber. This increased supply of air provides increased volumetric efficiency, resulting in an increased engine power output. However, it may be contemplated that when turbocharger delivers high supercharging pressures, the compressor components experience high thermal loading and stresses. This may necessitate that such compressor components are either fabricated from high-temperature materials. For example, nowadays titanium based compressor wheels instead of aluminum based compressor wheels are typically used in the turbocharger because of high temperature capability of titanium alloy. However, such titanium alloys are expensive and moreover such compressor wheels are costly to manufacture as titanium alloys are difficult to machine and/or more hazardous to cast. Therefore, it may be desirable to cool the compressor, and thereby the compressor wheel so it may be reverted back to be formed of relatively lower cost aluminum based materials, which also have relatively faster response being lightweight.

The present disclosure provides a method900for cooling the compressor124in a natural gas based combustion engine, such as the engine100, as depicted in the form of a flowchart inFIG. 9. At step902, the method900includes diverting at least a portion of natural gas from the fuel tank108of the engine100, with or without using the diverter valve142. At step904, the method900includes routing the portion of natural gas towards the compressor124, via the fluid line140. At step906, the method900includes providing one or more nozzles160disposed at one or more strategic locations of the compressor124. At step908, the method900includes injecting the portion of natural gas, via the one or more nozzles160, inside the compressor124. At step910, the method900includes allowing the portion of natural gas to diffuse with the compressed working fluid inside the compressor124in an endothermic expansion process as a result of Joule-Thomson effect (JTE), and thereby convectively cool the compressor124.

The present disclosure also provides a method1000of assembling the turbocharger assembly120for a natural gas based combustion engine, such as the engine100, as depicted in the form of a flowchart inFIG. 10. At step1002, the method1000includes providing the center housing130. At step1004, the method1000includes installing the compressor124onto the center housing130. At step1006, the method1000includes providing the fluid conduit140to connect the compressor124to the fuel tank108of the engine100. At step1008, the method1000further includes installing one or more nozzles160at one or more strategic locations of the compressor124. Optionally, the method1000may include installing the one or more nozzles160at the back-plate138of the compressor124. Optionally, the method1000may include installing the one or more nozzles160at the exducer section139of the compressor124. Optionally, the method1000may include installing the one or more nozzles160proximal to the inlet136of the compressor housing128. Optionally, the method1000may include arranging the nozzles160around the compressor wheel132in a ring shaped manner.

It is estimated that the temperature of the charged air inside the compressor124may be dropped by about 18 to 23° C., or an average of about 20° C., using the systems and methods of the present disclosure. The estimation is made based on following points: 1) The temperature of natural gas lowers by approximately 3.9° C. per 100 psi pressure drop. Since the CNG is stored at about 3600 psi, total pressure drop may lower natural gas temperature by approximately 140° C.; 2) The mass air to fuel ratio of natural gas in the engine100is usually about 17:1; and 3) The heat capacity of natural gas at atmosphere condition is approximately 2.34 KJ/Kg-K, and of air is approximately 1.0 KJ/Kg-K. Factoring these, it is possible to achieve a temperature drop of about 18 to 23° C. A temperature drop of 20° C. could enable an increase of compression ratio, e.g. from 6.2 to 6.8 at 74% compressor efficiency. Such magnitude of temperature drop of the charged air, and thereby the compressor wheel132, may not only help to increase the volumetric efficiency, but also provide the possibility for certain applications to switch from using titanium based compressor wheels to using aluminum alloys based compressor wheels. It may be understood that the average temperature drop of about 20° C. is the overall average temperature drop assuming the gases are completely and uniformly mixed. However locally at or near the CNG injection locations, the temperature drop is expected to be much more severe. Thus if the injection locations are strategically selected at high temperature locations of the compressor wheels, it would generate sufficient local temperature drop to revert titanium based compressor wheels back to aluminum alloys based compressor wheels, such as aluminum alloy like FFM2618, and possibly even cast aluminum alloy like A354.

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 and assemblies 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.