GB2541230A

GB2541230A - A turbocharged automotive system comprising a long route EGR system

Info

Publication number: GB2541230A
Application number: GB1514396.9A
Authority: GB
Inventors: Racca Alberto
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2015-08-13
Filing date: 2015-08-13
Publication date: 2017-02-15
Also published as: GB201514396D0

Abstract

A turbocharged automotive system comprising a turbocharger compressor 240 and a long route Exhaust Gas Recirculation (EGR) system 600, the turbocharger compressor 240 being equipped with a water cooled housing 650, the long route EGR system 600 comprising a long route EGR circuit 610 equipped with a long route EGR cooler 640, and being provided with a mixing point 660 with an air intake duct 205 upstream of an inlet of the turbocharger compressor 240, wherein the EGR cooler 640 has an efficiency that is at least 10% lower than a baseline long route EGR cooler efficiency and a resulting permeability that is higher than a baseline long route EGR cooler permeability. Another advantage of this system is the reduced level of condensate formation due to the relatively higher temperature of gas entering the compressor 240.

Description

A TURBOCHARGED AUTOMOTIVE SYSTEM COMPRISING A LONG ROUTE EGR

SYSTEM

TECHNICAL FIELD

The technical field relates to a turbocharged automotive system comprising a turbocharger compressor and a long route Exhaust Gas Recirculation (EGR) system. BACKGROUND

Internal combustion engines may be provided with a forced air system such as a turbocharger in order to increase an engine efficiency and power by forcing extra air into the combustion chambers of the cylinders.

The turbocharger comprises a compressor rotationally coupled to a turbine.

Some modern compressors are equipped with water cooling circuit(s) provided into the compressor housing for Full Load performance improvement purposes.

Furthermore, in order to reduce NOx polluting emissions, turbocharged automotive systems may comprise an exhaust gas recirculation (EGR) system, which is provided for routing back and mixing an appropriate amount of exhaust gases with the fresh induction air entrained into the engine.

Advanced EGR systems comprise a first EGR conduit which connects the exhaust manifold with the intake manifold, and a second EGR conduit which connects the exhaust line downstream of the aftertreatment systems to the intake line upstream the intake manifold and is connected therein by the interposition of three-way valve or by other means. The first EGR conduit is also known as “short route EGR”. The second EGR conduit defines instead a “long route” which comprises also a relevant portion of the exhaust line and a relevant portion of the intake line. It has to be noted that the long route Exhaust Gas Recirculation (LR-EGR) is also known in the art as low pressure Exhaust Gas Recirculation (LP-EGR).

In this way, the long route EGR is effective for routing back to the intake manifold a portion of the exhaust gases while also increasing the enthalpy to the turbine.

According to the prior art, the selection of the LR-EGR cooler characteristics Is driven by a trade-off between efficiency and permeability, aimed at minimizing the Brake Specific Fuel Consumption (BSFC) impact and protecting the compressor from overtemperature conditions during Part Load operations at mid-high loads.

This thermal constraint is not beneficial for operations at very low ambient temperature (e.g. -10°C) in which condensation issues could occur because of the mixing of the humid EGR flow with the cold air.

An object of an embodiment disclosed is to provide a turbocharged automotive system that may be protected from the risk of condensation at a mixing point between the air path and the long route EGR circuit while, at the same time, inducing a lower fuel consumption and lower CO2 emissions.

This and other objects are achieved by the embodiments of the invention as defined in the independent claims. The dependent claims include preferred and/or advantageous aspects of said embodiments.

SUMMARY

An embodiment of the disclosure provides a turbocharged automotive system comprising a turbocharger compressor and a long route Exhaust Gas Recirculation (EGR) system, the turbocharger compressor being equipped with a water cooled housing, the long route EGR system comprising a long route EGR circuit equipped with a long route EGR cooler, the long route EGR circuit being provided with a mixing point with an air intake duct upstream of an inlet of the turbocharger compressor, wherein the long route EGR cooler has an efficiency that is at least 10% lower than a baseline long route EGR cooler efficiency and a resulting higher permeability that is higher than a baseline long route EGR cooler permeability.

An advantage of this embodiment is that the presence of a water cooled housing in the turbocharger compressor allows a considerable reduction of the LR-EGR cooler efficiency. In this way, a higher temperature for the EGR gases is expected at the long route EGR cooler outlet and, consequently, there is the possibility of increasing the average temperature of the gases above the dew point at the mixing with the cold air from the air path, obtaining an enhanced condensation protection for Part Load operations at low ambient temperature. A further advantage of this embodiment is that a cooler with higher permeability reduces the pumping losses in the Part Load area of the cycle because a lower throttling of the air flap is required to drive the correct EGR rate. This induces a lower fuel consumption due to lower pressure losses through the EGR cooler and therefore induces lower CO2 emissions.

According to another embodiment, the long route EGR cooler has an efficiency that is at least 20% lower than a baseline long route EGR cooler efficiency.

An advantage of this embodiment is that it provides an enhanced condensation protection for Part Load operations at low ambient temperature.

According to another embodiment, the water cooled housing of the turbocharger compressor is connected to an engine low temperature coolant circuit.

An advantage of this embodiment is that it allows the possibility of minimizing the LR-EGR cooler efficiency, reducing the condensation formation at very low ambient temperatures.

Also, this embodiment avoids deterioration of compressor efficiency in Part Load points at mid-low loads for operations at standard ambient temperature.

In general, high temperatures in the coolant circuit tend to increase the temperature of the flow inside the compressor, decreasing its efficiency. This has to be avoided, especially in low load points (with high weights in the various homologation cycles), to avoid to incur in BSFC deteriorations.

Furthermore, by maximization of the compressor cooling a minimization of the long route EGR cooler efficiency may be obtained and, if the same packaging constraints are maintained, a higher permeability circuit is obtained.

According to another embodiment of the invention, the water temperature in the engine low temperature coolant circuit does not exceed 50°C.

An advantage of this embodiment is that a 50°C coolant temperature is above the water saturation temperature: no condensation risks would occur because of the introduction of the cooling channel, neither in a condition of perfect thermal exchange.

The invention further comprises a long route EGR cooler designed with an efficiency that is at least 10% lower than a baseline long route EGR cooler efficiency for use in a turbocharged automotive system as above detailed.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments will now be described, by way of example, with reference to the accompanying drawings, wherein like numerals denote like elements, and in which:

Figure 1 shows an automotive system;

Figure 2 is a cross-section of an internal combustion engine belonging to the automotive system of figure 1;

Figure 3 shows a portion of the automotive system of Figure 1, according to an embodiment of the invention;

Figure 4 shows a graph representing a long route EGR cooler efficiency gap at a chosen mass flow rate for different EGR coolers; and

Figure 5 shows a comparative graph of the difference of temperatures with respect to the dew point at a mixing point between an air path and the EGR system between a baseline system and a system according to an embodiment of the invention.

DETAILED DESCRIPTION

Exemplary embodiments will now be described with reference to the enclosed drawings without intent to limit application and uses.

Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increases the pressure of the fuel received from a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200.

In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200.

In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. A charge air cooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move a rack of vanes 295 in different positions, namely from a fully closed position to a fully open position, to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust gases of the engine are directed into an exhaust system 270.

The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters.

Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

While the first EGR conduit defines a short route for the exhaust gas recirculation, in accordance with the present invention, a second EGR conduit 600 fluidly connects the exhaust line downstream of the aftertreatment systems to the intake line upstream the intake manifold and is connected therein by the interposition of a three-way valve or by two different valves. The second EGR conduit 600 defines a long route which comprises also a relevant portion of the exhaust line and a relevant portion of the intake line.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110 and with a memory system and an interface bus. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor that may be integral within glow plugs 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal 447 position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, a Variable Geometry Turbine (VGT) actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Figure 3 shows a portion of the automotive system 100 of Figure 1, wherein a long route Exhaust Gas Recirculation (EGR) system 600 for a turbocharged automotive system 100 comprising a turbocharger compressor 240 is represented.

The compressor 240 comprises a water cooled housing 650, namely a water cooled circuit is provided in the housing 650 of the compressor 240 to cool down the compressor 240 during operations.

In an embodiment of the invention, the turbocharger compressor 240 may be equipped with a first cooling circuit in the scroll and a second cooling circuit in the back plate of the compressor. Other cooling circuit configurations may be used, provided that they obtain the effect of lowering the compressor outlet temperature.

Furthermore, the water cooled housing 650 of the turbocharger compressor 240 may be connected to an engine low temperature coolant circuit.

The water temperature in the engine low temperature coolant circuit does not exceed 50“C. A 50°C coolant temperature is above the water saturation temperature: no condensation risks would occur because of the introduction of the cooling channel, neither in a condition of perfect thermal exchange.

The long route EGR system 600 comprises a long route EGR circuit 610 equipped with a long route EGR cooler 640.

Downstream of the long route EGR cooler 640, an EGR valve 630 is provided to regulate the flow of EGR gases into the air intake duct 205, while downstream of an air filter (not represented for simplicity), an air intake valve 620 is provided.

Downstream of the EGR valve 630 and of the air intake valve 620, a mixing point 660 where the air and the long route EGR gases meet can be identified.

In other embodiments, the EGR valve 630 and the air intake valve 620 can be substituted by a single three-way EGR valve (not represented for simplicity), the three-way EGR valve intercepting the air intake duct 205 and the long route EGR circuit 610 and the mixing point 660 would be located inside the single three-way EGR valve.

The layout of Figure 3 represents therefore the combination of a long route EGR system 600 equipped with a long route EGR cooler 640 and a compressor 240 equipped with a water cooled housing 650.

According to an embodiment of the invention, the long route EGR cooler 640 is designed with an efficiency that is at least 10% lower than a baseline long route EGR cooler efficiency. A baseline long route EGR cooler efficiency may be defined as an efficiency greater than 95% for mass flow rates on gas side lower than 20 kg/h.

Figure 4 shows a graph representing a long route EGR cooler efficiency gap at a chosen mass flow rate for different EGR coolers.

In particular, Figure 4 shows - for example - a baseline efficiency point A (namely 95% at 20kg/h) as compared to an efficiency point B for a less efficient long route EGR cooler 640 according to an embodiment of the invention (namely 75% at 20kg/h). A reduced efficiency of the EGR cooler 640 raises the temperature at the mixing point, driving the mixture upstream the impeller above the dew point in operations at low ambient conditions. This reduces the risk of water droplets formation that are dangerous for the compressor wheel durability. A reduced efficiency of the EGR cooler 640 of for example 10% can be obtained, for example, by redesigning a traditional EGR cooler 640 by reducing the surface of thermal exchange.

In an advantageous embodiment of the invention, the long route EGR cooler is designed with an efficiency that is at least 20% lower than a baseline long route EGR cooler efficiency.

Furthermore, according to an embodiment of the invention, the long route EGR cooler 640 is designed with a permeability that is higher than a baseline long route EGR cooler permeability. A baseline long route EGR cooler permeability may be defined as the permeability of an EGR cooler having a baseline efficiency as above detailed. A second step in the assessment of the layout according to the various embodiment of the invention has been the evaluation of the condensation occurrence at the mixing point 660 between the EGR circuit 610 and the air intake duct 205 upstream of the compressor 240 at low ambient temperature, in order to explore a possible severe condition to be taken into account for future regulations.

The simulation has been run with the same targets of boost and EGR rate as the baseline model. A calculation has been performed in order to check if any saturation conditions occur in the mixing point 660, with no resolution about the spatial distribution of the water droplets, as no water formation in front of the compressor is presumed to be tolerated.

The outcome is summarized in Figure 5 where the dew temperature is calculated for a set of engine working points. Figure 5 shows a comparative graph of the difference of temperatures with respect to the dew point at a mixing point between an air path and the EGR system between a baseline system and a system according to an embodiment of the invention.

In other words, the graph of Figure 5 shows curves E and F representing a difference of temperature Delta between the actual temperature at the mixing point and the theoretical dew point temperature: Delta = Tmixing - Tdew points- If Delta is < 0 condensation occurs at the mixing point in front of the compressor.

Curve E represents a baseline system, curve F a system according to an embodiment of the invention.

In particular, a comparison is offered between the expected condensation formation at -15°C ambient temperature for the original baseline layout (curve E) versus the layout according to the various embodiments of the invention (curve F).

Even if the condensation risk is not totally removed, the new features introduced into the system are effective in mitigating the occurrence of saturation conditions.

It must also be noted that the EGR cooler, as designed according to the various embodiments of the invention, to avoid condensation leads also to higher permeability, which is translated in lower BSFC.

It must also be noted that the increase of permeability of the EGR cooler, as designed according to the various embodiments of the invention, is a direct consequence of the intended reduction of efficiency in its design, which is normally not allowed by the common prior art in EGR cooler design rules; this fact is also a testimonial of the originality and inventive step of the various embodiments of the invention.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCE NUMBERS 100 automotive system 110 internal combustion engine (ICE) 120 engine block 125 cylinder 130 cylinder head 135 camshaft 140 piston 145 crankshaft 150 combustion chamber 155 cam phaser 160 fuel injector 170 fuel rail 180 fuel pump 190 fuel source 200 intake manifold 205 air intake duct 210 intake air port 215 valves of the cylinder 220 exhaust gas port 225 exhaust manifold 230 high pressure turbocharger 240 high pressure compressor 250 high pressure turbine 260 charge air cooler 270 exhaust system 275 exhaust pipe 280 exhaust aftertreatment device 290 VGT actuator 295 rack of vanes of the turbine 300 EGR system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensor 445 accelerator pedal position sensor 447 accelerator pedal 450 electronic control unit (ECU) 600 long route EGR system 610 long route EGR circuit 620 air intake valve 630 long route EGR valve 640 long route EGR cooler 650 compressor water cooling housing 660 mixing point

Claims

1. A turbocharged automotive system (100) comprising a turbocharger compressor (240) and a long route Exhaust Gas Recirculation (EGR) system (600), the turbocharger compressor (240) being equipped with a water cooled housing (650), the long route EGR system (600) comprising a long route EGR circuit (610) equipped with a long route EGR cooler (640), the long route EGR circuit (610) being provided with a mixing point (660) with an air intake duct (205) upstream of an inlet of the turbocharger compressor (240), wherein the long route EGR cooler (640) has an efficiency that is at least 10% lower than a baseline long route EGR cooler efficiency and a resulting higher permeability that is higher than a baseline long route EGR cooler permeability.

2. The turbocharged automotive system (100) according to claim 1, wherein the long route EGR cooler (640) has an efficiency that is at least 20% lower than a baseline long route EGR cooler efficiency.

3. The turbocharged automotive system (100) according to claim 1, wherein the water cooled housing (650) of the turbocharger compressor (240) is connected to an engine low temperature coolant circuit.

4. The turbocharged automotive system (100) according to claim 1, wherein the water temperature in the engine low temperature coolant circuit does not exceed 50eC.

5. A long route EGR cooler (640) designed with an efficiency that is at least 10% lower than a baseline long route EGR cooler efficiency for use in a turbocharged automotive system (100) according to any of the preceding claims.