NL2026301B1

NL2026301B1 - Alternative Turbo Compounding

Info

Publication number: NL2026301B1
Application number: NL2026301A
Authority: NL
Inventors: De Jong Dirk-Jan
Original assignee: Daf Trucks Nv
Priority date: 2020-08-19
Filing date: 2020-08-19
Publication date: 2022-04-14

Abstract

An internal combustion engine (100) producing exhaust gas, comprisingat least one exhaust manifold (160), arranged for collecting exhaust gas from at least one cylinder (110) of the internal combustion engine (100) and delivering said exhaust gas to an exhaust line (202) of the internal combustion engine (100) and comprising an EGR line (303), arranged for recirculating part of the exhaust gas flowing through the exhaust line (202) of the internal combustion engine to an intake line (404) of the internal combustion engine (100) and comprising a turbocharger (700), comprising a turbine (710) arranged for extracting energy from the exhaust gas in the exhaust line (202) downstream of the EGR line (303) and a compressor (720) in the intake line (404), said turbine (710) arranged to drive the compressor (720) and comprising at least one power turbine (510), arranged for extracting energy from the exhaust gas upstream of the EGR line (303) and comprising whereas each power turbine (510) is arranged for expanding exhaust gas delivered by at least one exhaust manifold (160).

Description

P127636NL00 Title: Alternative Turbo Compounding The invention relates to a compound turbo for an internal combustion engine.

Description of the prior art One of the methods to increase the efficiency of internal combustion engines — i.e, reduce the ratio of fuel use to power — involves the use of a turbo-compound. In a turbo-compound engine, the internal combustion engine comprises one or more turbines arranged to recover energy from the exhaust gas of the engine. The recovered energy can e.g. be used to drive a turbocharger, be used to drive the output shaft of the engine, or be stored for later or different use. In standard turbo- compound engines, a power turbine is arranged in the exhaust line downstream of a turbocharger, to extract additional power from the exhaust gases. This power can be used to assist the engine through a gearbox or generate electricity through a generator.

Compared to conventional internal combustion engines, turbo-compound engines typically have an increased back pressure on the cylinders, due to the presence of the turbines which causes an increased resistance of the exhaust system to discharge the exhaust gas into the atmosphere. The increased back pressure initially leads to a drop in engine power. Still, due to the energy recovered from the exhaust gas by the turbines, the total net power produced is higher for turbo-compound engines than for conventional internal combustion engines.

Nowadays the use of exhaust gas recirculation (EGR) has become a common requirement for engines, to comply with legislation on NOx emission. With an EGR line, part of the exhaust gas is recirculated into the intake line of the engine. Typically, a so called HP-EGR system is used, where the EGR hne is branched off directly from the exhaust manifold and into the intake line near to the intake manifold, or directly into the intake manifold. This allows the EGR line to be short and close to the engine, thereby reducing pressure losses and the overall size and weight of the internal combustion engine.

However, when a turbo-compound engine is equipped with EGR, part of the high pressure exhaust flow is taken away from the exhaust line before it can expand through the turbine(s). Assuming the back pressure remains equal, the total net power developed by the engine is reduced. The result is that the effectiveness of turbo-compound is limited on engines with EGR. It 1s difficult to propose a solution that synergistically combines the positive effects of EGR and turbo-compound, such that an internal combustion engine is created with increased efficiency as well as reduced emission of NOx, without any modifications to commonly used engine configurations or components.

Summary of the invention In one aspect, it is aimed to provide an internal combustion engine producing exhaust gas, and comprising at least one exhaust manifold. Each exhaust manifold is arranged for collecting exhaust gas from at least one cylinder of the internal combustion engine, and delivering the exhaust gas to an exhaust line. The internal combustion engine further comprises an exhaust gas recirculation (EGR) line, a turbocharger, and at least one power turbine.

The EGR line is arranged for recirculating part of the exhaust gas flowing through the exhaust line to an intake line of the internal combustion engine. The turbocharger has a turbine, arranged for extracting energy from the exhaust gas in the exhaust line downstream of the EGR line. The turbocharger has a compressor in the intake line, whereas said turbine is arranged to drive said compressor. The at least one power turbine is arranged for extracting energy from the exhaust gas upstream of the EGR line.

Said at least one power turbine is arranged for expanding exhaust gas delivered by at least one exhaust manifold to reduce the exhaust gas pressure in the exhaust line upstream of the turbocharger turbine.

Optionally, the exhaust manifold & power turbine may be arranged for pulse charging by for collecting exhaust gas from a maximum of four, preferably three, cylinders of the internal combustion engine.

Each power turbine may comprise a number of entry ports, arranged for separately receiving exhaust gas from an equal number of exhaust manifolds of the internal combustion engine, Each power turbine may be a high pressure turbine, e.g. having a pressure ratio preferably smaller than 2. Optionally, the at least one power turbine and/or the turbocharger turbine may be arranged for driving an electric generator and/or a mechanical transmission. The turbocharger and at least one power turbine may be coupled by a single shaft or mechanical transmission to form a combined turbine. In another aspect of the invention, the EGR line may comprise an EGR cooler arranged for dissipating heat from the exhaust gas in the EGR line to reduce the exhaust gas temperature before entering the intake line. The at least one power turbine may be arranged for expanding the exhaust gas to reduce the exhaust gas temperature upstream of the EGR cooler, such that the EGR cooler may dissipate less heat from the exhaust gas. Optionally, the internal combustion engine may comprise an additional further power turbine arranged for extracting energy from the exhaust gas in the exhaust line downstream of the turbocharger turbine, whereas the additional further power turbine may be arranged for driving an electric generator and/or a mechanical transmission.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further elucidated in the figures: Figures 1A and 1B provide schematic representations of a conventional turbo-compound engine with EGR and an internal combustion engine according to the invention; Figure 2 provides a graph comparing the net power output of various internal combustion engine configurations;

Figure 3 shows an internal combustion engine according to a first embodiment of the invention; Figure 4 shows an embodiment of the invention, comprising multiple parallel power turbines; Figure 5 shows an embodiment of the invention, comprising a multiple entry power turbine; Figure 6 shows an embodiment of the invention, comprising a power turbine arranged for driving a mechanical transmission; Figure 7 shows an embodiment of the invention, comprising a turbocharger and a power turbine coupled by a mechanical transmission; Figure 8 shows an embodiment of the invention, comprising a turbocharger arranged for driving an electric generator; Figure 9 shows an embodiment of the invention, comprising an additional power turbine downstream of the turbocharger.

DETAILED DESCRIPTION Turning to Figures 1A and 1B, there is provided schematic representations of two different internal combustion engines (ICE) producing a flow of exhaust gas.

Figures 1A and 1B both comprise a high-pressure exhaust gas recirculation (EGR) line, and a turbocharger and power turbine serially arranged in an exhaust line of the engine. The EGR line is arranged for recirculating part of the exhaust gas to an intake line (not shown) of the engine, to reduce the emission of NOx into the atmosphere. The turbocharger comprises a turbine arranged for extracting energy from the exhaust gas, and a compressor arranged for boosting pressure in the intake line of the engine, said turbine arranged to drive said compressor. The power turbine is arranged for recovering additional energy from the exhaust gas, e.g. to increase power of the engine or to power electronic components in the vehicle driven by the engine.

Figure 1A shows a conventional turbo-compound engine with EGR, wherein the EGR line is branched off from the exhaust line upstream of the turbocharger and the power turbine is arranged downstream of the turbocharger. The disadvantage of this configuration with respect to a conventional turbo-compound engine without EGR is that exhaust gas is passed through the power turbine with a reduced flow and pressure, due to a part of the exhaust gas produced by the internal combustion engine being branched off to the EGR line. The reduced flow and pressure through the power turbine leads to a reduced amount of energy that 5 can be recovered from the exhaust gas by the power turbine.

This is shown in a graph in Figure 2. Initially, the net increase in power output obtained by a conventional turbo-compound is diminished by adding EGR. While the power output of the engine remains equal due to an unchanged backpressure on the engine, the power output of the power turbine is reduced.

However, the current invention proposes a new turbo-compound with EGR with improved net power output with respect to a conventional turbo-compound without EGR, due to a more efficient use of the back pressure, Figure 1B shows an internal combustion engine according to the invention, wherein at least one power turbine is arranged for extracting energy from the exhaust gas upstream of the EGR line, which power turbine is arranged for expanding exhaust gas delivered by at least one exhaust manifold to reduce the exhaust gas pressure in the exhaust line upstream of the turbocharger turbine. In this way, the full flow of exhaust gas produced by the engine is passed through the power turbine prior to a part of the flow being branched off to the EGR line. As a result, a maximum amount of energy can be recovered from the exhaust gas by the power turbine.

Due to identical numbers and types of components used, the configurations depicted in Figures 1A and 1B have an equal amount of back pressure on the engine, In both configurations, the turbocharger is arranged downstream of the EGR line, thus the flow of exhaust gas through the turbocharger, and therefore the amount of energy that can be extracted by the turbocharger, is equal in both configurations. However, since in Figure 1B the power turbine is able to process the full flow of exhaust gas produced by the engine, the net amount of energy that can be recovered from the exhaust gas is higher in the internal combustion engine according to the invention with respect to a conventional turbo-compound engine.

Advantageously, the power turbine is arranged for expanding exhaust gas to reduce the pressure in the flow of exhaust gas upstream of the turbocharger turbine, such that the back pressure can be used more efficiently. This can e.g. be achieved with a configuration comprising a smaller, high-pressure power turbine upstream of a larger turbocharger turbine operating at a reduced pressure compared to the high pressure power turbine. In this way, the operating ranges of both types of turbines can be made complementary to each other.

Advantageously, as the power turbine is arranged for expanding exhaust gas upstream of the turbocharger turbine, the pressure ratio & volume flow of this turbocharger turbine will largely equal to current practice, so only small modifications to existing turbochargers are required.

Preferably, the power turbine has a pressure ratio smaller than 2, more preferably smaller than 1.5.

Figure 3 shows an embodiment of an internal combustion engine 100 comprising an exhaust manifold 160 arranged for collecting exhaust gas from a number of cylinders 110 of the internal combustion engine 100 and delivering the exhaust gas to an exhaust line 202. The full flow of exhaust gas is passed through a power turbine 510, arranged for extracting energy from the exhaust gas downstream of the exhaust manifold 160. The extracted energy may be used e.g. to drive an electric generator 550 and/or a mechanical transmission (not shown).

The electric generator may be utilized for driving an electric motor in a hybrid vehicle, arranged for assisting the internal combustion engine or driving one or multiple wheels of the vehicle independently from the internal combustion engine. Alternatively or additionally, the electric generator may be used to charge one or multiple batteries and/or power other electric components that may be present in the vehicle driven by the internal combustion engine.

Downstream of the power turbine 510 a part of the exhaust gas is branched off to an EGR line 303, arranged for recirculating the exhaust gas from the exhaust line 202 to an intake line 404 of the internal combustion engine 100.

Another part of the exhaust gas is transported by the exhaust line 202 through a turbine 710 of a turbocharger 700, arranged for extracting energy from the exhaust gas downstream of the EGR line 303 to boost pressure in the intake line 404 by means of a compressor 720.

The power turbine 510 is arranged for expanding the exhaust gas delivered by the exhaust manifold 160 to reduce the exhaust gas pressure in the exhaust line 202 upstream of the turbocharger turbine 710, such that the turbocharger 700 extracts energy from the exhaust gas at peak efficiency. Figure 4 & 5 show an embodiment of an internal combustion engine 100 according to the invention, laid out for the use of pulse charging, by having multiple exhaust manifolds 160 that each collect exhaust gas from a subset of cylinders 110 of the internal combustion engine 100, thereby forming separate engine blocks.

By having separate engine blocks with cylinders having their firing interval either simultaneous or separated by minimal 180 °CA, preferably 220 °CA, overlap between exhaust pulses, and therefore a decrease in pulse energy of the exhaust gas, can be avoided. Combined with the fact that all exhaust gases are sent to the power turbine(s) this means the ratio of available energy before the turbine versus the piston pumping work is improved.

To achieve the benefits of pulse charging a maximum of 4, preferably 3 cylinders per isolated engine block are connected to one turbine inlet through manifolds having a volume of preferably less than 4 times the cylinder swept volume and a diameter of less than 40% of the piston diameter.

Optimally, three cylinders 110 are connected to each exhaust manifold 160, with the cylinders selected such that quiescent periods as well as overlap between exhaust pulses is minimized. This arrangement may generate higher engine efficiency through reduction of pumping losses. However, due to reasons of e.g. specific power output or balancing, some engines commonly utilize a maximum of four cylinders 110 per exhaust manifold 160.

Each exhaust manifold 160 may be arranged to deliver exhaust gas to a power turbine 510, creating a parallel arrangement of a number of power turbines 510 equal to the number of exhaust manifolds 160. Each power turbine may drive an electric generator and/or a mechanical transmission. The benefit of this arrangement is that each power turbine 510 receives exhaust gas containing a maximum amount of (pulse) energy. After passing through the power turbines 510, all exhaust gas 1s collected in the exhaust line 202 upstream of the EGR line 303 for further downstream transport.

Alternatively, Figure 5 shows an embodiment of an internal combustion engine 100 according to the invention, whereas instead of multiple turbines 510 (from fig. 4) at least one power turbine 510 comprises multiple entry points 525a, 525b, arranged for separately receiving exhaust gas from an equal number of exhaust manifolds 160 of the internal combustion engine 100. This so called multiple entry (twin entry) turbine beneficially allows to separately utilize, and therefore preserve, the exhaust pressure pulses (and thus energy) from each exhaust manifold 160 in a per se known manner.

The multiple entry power turbine 510 may comprise any number of entry points deemed practical. It may e.g. be configured as a twin-entry or double entry turbine, in which each entry point 525a, 525b receives exhaust gas from one exhaust manifold 160 and feeds the rotor along the entire circumference of the turbine, or feeds separate sections of the rotor, respectively. The maximized energy in the separate flows of exhaust gas delivered to the multiple entry power turbine 5101s merged and converted into kinetic energy by the power turbine, and can in turn be utilized to drive an electric generator and/or a mechanical transmission. As such, a multiple entry power turbine 510 may provide an alternative option to further improve the energy efficiency of the internal combustion engine 100.

Figure 6 shows an embodiment of an internal combustion engine 100 according to the invention, comprising a power turbine 510 optionally arranged for driving a mechanical transmission 800. The mechanical transmission 800 may be arranged for transferring energy from the power turbine 510 to a load, which may e.g. be an electric generator 550 or the crank shaft of the internal combustion engine 100.

The mechanical transmission 800 may comprise multiple parallel or serial paths, arranged to transfer energy to multiple loads. The mechanical transmission 800 may comprise a clutching, distributing or switching arrangement to selectively couple or decouple a load to the power turbine 510 and/or to selectively adjust the relative amount of energy that is transferred from the power turbine 510 to a load.

For this purpose, the mechanical transmission 800 may comprise e.g. gears, push or pull belts, snares, pulleys, chains, friction couplings, (hydraulic or viscous) clutch plates, or other means suitable for transferring mechanical energy.

As an additional feature (see Figure 7), one or multiple power turbines 510 may be coupled by means of a mechanical transmission 800 to the turbocharger turbine 710 to form a combined turbine, which allows balancing of the exhaust gas pressure load between the power turbine(s) 510 and the turbocharger turbine 710, e.g. as a two-stage turbo. In congruence with the current invention, in a first stage the flow of exhaust gas is passed through the power turbine(s) 510 and in a second stage the exhaust gas is passed through the turbocharger turbine 710. The EGR line 303 is branched off from the exhaust line 202 between the first and second stage.

The mechanical transmission 800 may comprise a single shaft on which the power turbine(s) 510 and the turbocharger turbine 710 are mounted. Alternatively, the mechanical transmission 800 may comprise e.g. gears, belts, chains, friction couplings or any other means suitable for transferring torque between multiple shafts.

In Figure 8, an embodiment is shown of an internal combustion engine 100 according to the invention, additionally comprising an EGR cooler 390 arranged for cooling the exhaust gas passing through the EGR line 303, Cooling may be done actively, e.g. forced heat transfer by means of an induced flow of air or cooling fluid, or passively, e.g. heat transfer by means of cooling fins.

The at least one power turbine 510 is arranged for extracting energy, and thus temperature, from the exhaust gas upstream of the EGR line 303. To optimize the energy efficiency of the internal combustion engine 100, the power turbine(s) may be arranged such that the exhaust gas temperature is already reduced upstream of the EGR cooler 390 which relieves EGR cooler 390. Since the exhaust gas is cooled prior to passing through the EGR line 303, an active EGR cooler 390 may need less power and a passive EGR cooler may be smaller in size, while still being able to dissipate heat from the exhaust gas down to a desired temperature. As a consequence, the load on the internal combustion engine is reduced, thereby improving the energy efficiency of the engine.

In the current invention the at least one power turbine 510 is arranged to extract energy from the exhaust gas upstream of the turbocharger 700, such that the turbocharger 700 and potentially also an EGR cooler can operate at peak efficiency.

In some cases, it might also be preferred to extract work from the turbocharger 700 itself. For instance, the turbocharger 700 may be arranged to drive an electric generator 510, as shown in Figure 8.

The electric generator may be driven by the turbocharger turbine 710 or by the compressor 720. Energy may be transferred to the electric generator 510 directly, via a single shaft, or may be transferred by means of a mechanical transmission 800 comprising e.g. gears, belts, chains, friction elements, or other means to transfer torque via multiple shafts.

Alternatively, the turbocharger 700 may comprise a mechanical transmission 800 arranged to drive the internal combustion engine 100, parts thereof, or other components in a vehicle driven by the internal combustion engine

100. Figure 9 shows an embodiment of an internal combustion engine 100 according to the invention, comprising an additional power turbine 511 arranged for extracting energy from the exhaust gas in the exhaust line 202 downstream of the turbocharger 700. This optional additional feature may be implemented in case the exhaust gas is expected to contain a useful amount of energy after it has passed through the turbocharger turbine 710.

The energy extracted by the additional power turbine 510 may e.g. be used to drive an electric generator 510 directly or by means of a mechanical transmission 800. The generated electrical power may be used to increase the power of the internal combustion engine 100 (e.g. in case of a hybrid engine) or to power other electrical components in the vehicle driven by the internal combustion engine 100 (e.g. an air conditioning or heating system, or electric motors).

Alternatively by means of a mechanical transmission, the energy extracted by the additional power turbine 511 may e.g. be used to mechanically drive the internal combustion engine 100 or parts thereof, or other components in the vehicle driven by the internal combustion engine 100 (e.g. a pump).

Claims

Conclusions

An internal combustion engine (100) producing exhaust gas, comprising: — at least one exhaust manifold (160) adapted to collect exhaust gas from at least one cylinder (110) of the internal combustion engine (100) and supplying said exhaust gas at an exhaust line (202) of the internal combustion engine (100); - an EGR line (303) arranged to recirculate a portion of the exhaust gas flowing through the exhaust line (202) of the internal combustion engine (100) to an inlet line (404) of the internal combustion engine (100); — a turbocharger (700) comprising a turbine (710) for extracting energy from the exhaust gas in the exhaust line (202) downstream of the EGR line (303) and a compressor (720) in the inlet line (404), wherein said turbine (710) is arranged to drive the compressor (720); — at least one power turbine (510) adapted to extract energy from the exhaust gas upstream of the EGR line (303); wherein each power turbine (510) is configured to expand exhaust gas supplied from at least one exhaust manifold (160).

The internal combustion engine (100) of claim 1, wherein each exhaust manifold (160) is adapted to collect exhaust gas from a maximum of four cylinders (110) of the internal combustion engine (100).

An internal combustion engine (100) according to any preceding claim, wherein the at least one power turbine (510) includes a plurality of input ports (525) adapted to separately receive exhaust gas from an equal number of exhaust manifolds (160) of the internal combustion engine. combustion engine (100).

An internal combustion engine (100) according to any preceding claim, wherein each power turbine (510) is arranged to drive an electrical generator (550) and/or a mechanical transmission (800).

An internal combustion engine (100) according to any preceding claim, wherein each power turbine (510) has a pressure ratio that is less than 2.

An internal combustion engine (100) according to any preceding claim, wherein the turbocharger (700) and at least one power turbine (510) are coupled by a mechanical transmission (800) to form a combined turbine.

An internal combustion engine (100) according to any preceding claim, wherein the EGR line (303) includes an EGR cooler (390) adapted to remove heat from the exhaust gas in the EGR line (303) to reduce the temperature of decreasing the exhaust gas before it enters the intake line (404).

The internal combustion engine (100) of claim 7, wherein the at least one power turbine (510) is configured to expand the exhaust gas to lower the temperature of the exhaust gas upstream of the EGR cooler (390) such that the EGR cooler ( 390) dissipates heat at maximum efficiency.

An internal combustion engine (100) according to any one of the preceding claims, wherein the turbocharger turbine (710) is additionally arranged to drive an electrical generator (550) and/or a mechanical transmission (800).

An internal combustion engine (100) according to any preceding claim, including an additional power turbine (511) adapted to extract energy from the exhaust gas in the exhaust line (202) downstream of the turbocharger turbine (710).

An internal combustion engine (100) according to claim 10, wherein the additional power turbine (511) is adapted to drive an electrical generator (550) and/or a mechanical transmission (800).