WO2019129910A1

WO2019129910A1 - Device for recovering energy from combustion gas

Info

Publication number: WO2019129910A1
Application number: PCT/ES2018/070828
Authority: WO
Inventors: Jesús Vicente BENAJES CALVO; José María Desantes Fernandez; Antonio Garcia Martinez; Pedro PIQUERAS CABRERA; José Ramón SERRANO CRUZ
Original assignee: Universitat Politècnica De València
Priority date: 2017-12-27
Filing date: 2018-12-21
Publication date: 2019-07-04
Also published as: ES2657082B2; ES2657082A1

Abstract

The invention relates to a device for recovering energy from combustion gas produced in an internal combustion engine. The internal combustion engine comprises an engine block and a combustion gas post-treatment system. The energy recovery device is arranged downstream of the post-treatment system and comprises a first turbo-unit with a first turbine and a first compressor; an ejector; and an additional compressor, which is a second compressor that forms a second turbo-unit together with a second turbine located in the path of recirculated gas between the exhaust pipe and the intake pipe. This increases the gas intake pressure into the combustion energy and recovers the energy in the combustion gas, both the gas that is discharged into the atmosphere and the recirculated gas.

Description

GAS ENERGY RECOVERY EQUIPMENT FROM THE

COMBUSTION

Field of the invention

The present invention relates generally to the field of internal combustion engines of vehicles, and more specifically to the systems for recovering the energy of the gases coming from combustion in said internal combustion engines.

BACKGROUND OF THE INVENTION

The regulations regarding the compliance with polluting emissions in the transport and automotive sectors have become highly restrictive in recent years, especially for compression ignition engines that use diesel fuel. Due to the compromise between the emissions of soot and nitrogen oxides (NOx) in compression ignition engines it has become necessary to include post-treatment systems of gases from combustion whose function is the elimination of emissions contaminants, namely carbon monoxide (CO), unburned hydrocarbons (HC), particulate matter and nitrogen oxides (NOx), after they have been generated. Thus, post-treatment systems are essential today to achieve compliance with the regulations on polluting emissions.

The addition of said systems to the engine assembly implies a considerable increase in production costs as well as a greater complexity of the power plant. In addition, the correct operation of these systems requires the consumption of additional fluids in the exhaust line, such as urea for the reduction of NOx in selective catalytic reduction (SCR) systems, and eventually gasoil downstream of the turbine to increase the temperature of exhaust during the heating process of the engine.

In recent years, different low temperature combustion (LTC) strategies have been investigated that maintain or improve the consumption of conventional diesel combustion by reducing the formation of particulate matter and NOx in the combustion chamber of compression ignition engines and , therefore, mitigate the disadvantages generated by post-treatment systems as their requirements are lower. Despite its potential, the application of most LTC combustion concepts is restricted to half motor loads since they are mainly controlled by chemical kinetics, which means that there is no cycle to cycle control of the start of combustion by parameters of engine and the stability of combustion is compromised. At low loads, the flame may be extinguished, while at high loads detonation problems may occur. In this sense, the optimum fuel for LTC strategies depends on the operating conditions of the engine: at low loads, a high-reactivity fuel is necessary while, on the contrary, at high loads a low-reactivity fuel is necessary. Based on this fact, a LTC strategy called RCCI has been developed that uses two fuels of different reactivity. In particular, gasoline is injected as a low-reactivity fuel in the intake manifold and diesel fuel as a high-reactivity fuel directly in the combustion chamber. This concept makes it possible to vary the mixing ratio of both fuels instantaneously, which allows achieving the desired reactivity for each motor operation condition. Thus, the RCCI combustion strategy provides ultra low levels of particulate material and NOx, so that the post-treatment needs of both pollutants are significantly reduced. Said reduction occurs at the same time that the consumption of a conventional diesel combustion is improved. This is achieved through the use of high proportions of gasoline in the mixture and an optimized diesel fuel injection strategy.

Despite the clear advantages it presents, the concept has important challenges not yet resolved to be fully implemented in combustion engines, such as the need to recirculate large quantities of gases from combustion to admission, to reduce enough combustion temperature. The recirculation of gases from combustion involves removing a large amount of energy from said gases that in the prior art can not be recovered to supercharge the engine or other type of application. Another very important limitation is the low efficiency of combustion at low loads, understood as high emissions of carbon monoxide (CO) and unburned hydrocarbons (HC). These emissions come mainly from an excessive premix level between air and fuel as well as from the high volatility of low reactivity fuel. Additionally, and thanks to the high rate of recirculated gases, the temperature throughout the entire combustion process is low compared to a conventional diesel combustion and consequently the exhaust temperature is also. Thus, high levels of CO and HC together with low exhaust temperatures compromise the correct operation of the diesel oxidation catalyst (DOC).

In the art, internal combustion engines are already known which can operate in a low temperature combustion mode, in particular of the RCCI type, for example from the documents US2014032081A1 and US2012247421A1. It is also known to use energy recovery systems from the combustion gases that are evacuated to the atmosphere, for example from the US5611203A and EP2105596A2 documents.

However, the systems known in the prior art do not allow a sufficient use of the energy of the gases coming from the combustion and therefore are not suitable due to the high costs involved in the specific consumption of the engine.

For all the above, it is necessary to define a post-treatment system adequate to the requirements of the RCCI combustion concept as well as the definition of the exhaust and intake line that provide the adequate conditions for the control of the combustion process and the recovery of energy from the gases from combustion, both evacuated to the atmosphere and recirculated.

Summary of the invention

To solve the problems of the prior art, the present invention relates to a configuration for reciprocating internal combustion engines that takes advantage of synergies between the combustion process, the location of the post-treatment system aimed at reducing CO emissions and HC, the supercharging system and the design of the recirculated gas line to reduce consumption and polluting emissions.

Thus, the present invention discloses a device for recovering energy from gases coming from combustion in an internal combustion engine. The internal combustion engine comprises a motor block and a post-treatment system for gases from combustion.

The energy recovery equipment of the invention is disposed downstream of said post treatment system and comprises:

- a first turbogroup consisting of a first turbine and a first compressor to recover energy from the gases evacuated to the atmosphere; - an ejector to recover energy from the recirculated gases; Y

- an additional compressor, which is a second compressor forming a second turbogroup together with a second turbine;

- the second turbine of the second turbogroup, located in the line of recirculated gases between the exhaust line and the intake line, the recirculated gases expanding in said second turbine, allowing to obtain mechanical energy to drive the second compressor of the second turbogroup, in the that the flow pressure of the intake line is increased.

Thus, the energy recovery equipment of the present invention allows to increase the pressure of the admission gases to the combustion engine taking advantage of the energy coming from the combustion gases.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood with reference to the following drawings which illustrate preferred embodiments of the invention, provided by way of example, and which are not to be construed as limiting the invention in any way:

Figure 1 shows a general outline of an equipment according to the present invention.

Figure 2 shows a schematic of a gas energy recovery equipment from combustion comprising a first turbogroup, an ejector and an additional compressor.

Figure 3 shows a schematic of an equipment according to a preferred embodiment of the present invention.

Figure 4 shows a schematic of an equipment according to another preferred embodiment of the present invention.

Figure 5 shows a diagram of a team according to another preferred embodiment of the present invention.

Detailed description of the preferred embodiments

Referring first to Figure 1, the main components of the gas energy recovery equipment from combustion in an internal combustion engine according to the present invention will be described generally and broadly.

First, the internal combustion engine itself comprises a motor block (1) and a post-treatment system (2) for gases from combustion.

The engine block (1) can have any suitable number of cylinders capable of operating in low temperature combustion mode (LTC), in particular of the RCCI type. This type of combustion is particularly demanding from the point of view of compliance with the regulations on polluting emissions since it can lead to a high rate of CO and HC formation combined with gases from low temperature combustion in order to optimize the consumption specific.

The post-treatment system (2) for gases from combustion is located just after the engine block (1), upstream of a turbine (4) (pre-turbine location) which will be described later. In this location, the temperature of the gases coming from the combustion is maximum. The post-treatment system (2) comprises at least the functions of particulate filtering and oxidation of CO and HC. This allows to work always with recirculated gases free of soot and guarantees that the chemical energy released in the oxidation of the unburned hydrocarbons is used in the elements located downstream of said post-treatment system (2), in the form of both thermal energy as mechanical according to the process carried out, and both for recirculated gases as for the gases coming from the combustion of the engine that are going to be evacuated to the atmosphere.

According to alternative embodiments of the present invention, other post-treatment systems intended for the reduction of NOx emissions are also available, as is already known to the person skilled in the art. Also, the architecture of this post-treatment system (2) is not particularly limited, and any of the many possibilities known in the prior art can be employed. For example, the use of a diesel oxidation catalyst (DOC) may be used together with a diesel particulate filter (DPF), in any order between them; the use of a catalyzed particle filter; the use of a NOx trap (LNT) followed by a DPF; a DOC or LNT followed by a catalyzed particulate filter with NOx reduction function (SCRF); etc.

The energy recovery equipment itself is arranged downstream of the post-treatment system (2) and comprises a first turbogroup (5), an ejector (7) and an additional compressor. The additional compressor is part of a second turbogroup (9). The set of these three elements is designated schematically in Figure 1 by reference 3, while the ejector assembly (7) and the second turbogroup (9) is designated by reference 6.

The combustion gases evacuated to the atmosphere will always pass through a first turbine (4), which together with a first compressor (20) forms part of the first turbogroup (5). In this way, the size of the first turbogroup (5) will always adapt to fresh air entering the engine, reducing its size to the maximum possible and thus reducing the delay of the first turbogroup (5) before transient operating processes.

On the other hand, the recirculated gases will expand in a specific system (6). Said system (6) comprises a ejector (7) and a second turbogroup (9) constituted by a second turbine (8) and a second compressor (10). As will be described hereinafter, this combination results in different preferred configurations according to the relative disposition of the ejector (7) and the second turbogroup (9) as well as the first turbogroup (5) and the second turbogroup (9) . The use of these energy recovery systems in the recirculated gases allows avoiding the use of specific heat exchangers for this flow.

In figure 1 it can also be seen the exhaust line comprising, in a known manner and therefore not described in detail herein, the necessary conduits (11) (for simplicity, are indicated schematically in Figure 1) for coupling the different elements that compose it from the output of the engine block (12) to the outlet to the atmosphere (13), a post-treatment system (14) complementary to (2) to ensure compliance with the regulations on polluting emissions and an exhaust silencer system (15).

For its part, the intake line comprises, also in a manner known per se and therefore not described in detail herein, the necessary conduits (16) (for simplicity, are indicated only in Figure 1) for coupling the various elements that compose it from the entrance to the line from the atmosphere (17) to the entrance to the engine block (18), an air filter (19) and a heat exchanger (21), preferably intercooler type. The heat exchanger (21) is common for the mass flow of fresh air and recirculated gases which reduces the number of elements of this type with respect to the state of the art.

Figure 2 shows a device for recovering energy from combustion gases comprising a first turbogroup, an ejector and an additional compressor, which is a centrifugal compressor (22). The recirculated gases are high pressure and are clean when taken between the post-treatment system (2) pre-turbine and the first turbine (4) for the expansion of the gases from the combustion evacuated to the atmosphere. In the ejector (7) the energy present in the gases coming from the combustion is recovered, guaranteeing that:

• The pressure at the outlet of the ejector (7) is greater than the pressure of fresh air from the first compressor (20) of the first turbogroup (5) due to the compression experienced by this flow in the ejector (7).

• The pressure of the recirculated gases is greater than the pressure at the outlet of the ejector (7) due to the expansion they experience in the ejector itself (7).

• The temperature at the outlet of the ejector (7) is an intermediate value between the temperature of the recirculated gases, which are cooled in the expansion process in the ejector (7), and the temperature of the fresh air from the first compressor (20). ) of the first turbogroup (5).

The throat of the ejector (7) is of variable geometry (variable section) in order to allow regulating the mass flow of recirculated gases.

Downstream of the ejector (7) is located a heat exchanger (21), preferably of intercooler type, and downstream of the latter is the centrifugal compressor (22) driven mechanically by an electric motor or connected to the auxiliary power system of the engine. Between the heat exchanger (21) and the centrifugal compressor (22) is located a condensate separator (23), which protects the centrifugal compressor (22) from the impact of condensed liquids on the impeller. Figure 3 shows a device according to a preferred embodiment of the present invention, which uses a recirculated gas energy recovery system integrated in a turbo-supercharging system in two stages (series compressors). That is, as will be seen below, the first and second compressors (20, 10) are located in series while the first and second turbines (4, 8) are located in parallel. In particular, only the recirculated gases are directed from the outlet of the post-treatment system (2) to the inlet of the second turbine (8) of the second turbogroup (9). This second turbine (8) is of variable geometry to allow regulating the expense of recirculated gases. The expansion of the recirculated gases allows to obtain mechanical energy to drive the second compressor (10) of the second turbogroup (9) in which the pressure of the fresh air admitted by the engine is increased. The recirculated gases are then directed to an ejector (7) of fixed geometry in which they expand, giving rise to their cooling and to the increase in pressure of the fresh air, coming from the second compressor (10), with which they are mixed. With this configuration, the flow rate of recirculated gases is regulated by the position of the second turbine (8) of variable geometry. This avoids the direct strangulation of the flow of recirculated gases in the intake line, which reduces the work of pumping and avoids the penalty of consumption.

From the ejector (7) the mixture of fresh air and recirculated gases is led to a condensate separator (23) which protects the impact of condensed liquids on the impeller of the first compressor (20) of the first turbogroup (5) located below. This first compressor (20) increases the pressure of the mixed flow, in what supposes a third stage of compression, when operated by the mechanical work provided by the expansion of the gases evacuated to the atmosphere in the first turbine (4) of the first turbogroup (5), which can be of fixed geometry (instead of variable geometry) because of the high expansion ratio with which it will work.

This configuration allows to have turbines of small size given that each one of them will move approximately half of the flow of gases coming from combustion (high rate of recirculated gases in RCCI combustion systems) while the compressors in series will also be sized reduced. The second compressor (10) belonging to the second turbogroup (9) may be small because only the fresh air is transferred; the first compressor (20) belonging to the first turbogroup (5) operates at high pressure at the inlet thereof, which reduces the corrected expense and therefore the size needed for the compressor. The combination of two stages of turbo-supercharging in series together with the compression in the ejector (7) allows to obtain a very high boost pressure of the motor.

Referring now to Figure 4, an equipment according to another preferred embodiment of the present invention will be described. In this case, the equipment uses a recirculated gas energy recovery system consisting of the expansion of the recirculated gases in the second turbine (8) of the second turbogroup (9) and in the energy recovery in an ejector (7) located below in order to compress the flow of fresh air. As can be seen in Figure 4, in this third embodiment of the present invention the first and second compressors (20, 10) are located in parallel while the first and second turbines (4, 8) are also located in parallel.

The second turbine (8) of the second turbogroup (9) is of variable geometry since in this way it allows acting as a regulator of the flow of recirculated gases. In this case, the ejector (7) can have a throat of fixed geometry, so that the throttling in admission is avoided to regulate the rate of recirculated gases, which reduces the work of pumping and avoids penalties in consumption. This configuration reduces the pumping work despite the fact that the expense of recirculated gases requires controlling the pressure in the exhaust manifold, since a large part of the associated energy is recovered efficiently in the second turbogroup (9).

The recirculated gases expand in the nozzle of the ejector (7) allowing these gases to be precooled and the kinetic energy recovered, thus compressing the mixture of fresh air from the air filter (19) and recirculated gases. At the outlet of the ejector (7) is located once again a condensate separator (23) generated in the mixture of pre-cooled and wet recirculated gases and fresh air at room temperature. Then the mixture of fresh air and recirculated gases is directed to two centrifugal compressors (10, 20) installed in parallel. As in the previous cases, the first compressor (20) belongs to the first turbogroup (5) and is coupled to the first turbine (4) of gases evacuated to the atmosphere; while the second compressor (10) belongs to the second turbogroup (9) and is coupled to the second turbine (8) of recirculated gases.

In this case, the first turbine (4) of the first turbogroup (5) is also of variable geometry in order to regulate the corrected regime of both compressors so that their operating point is similar. This configuration guarantees very high recirculated gas rates, even during very dynamic transients (period in which, in the prior art, this expense is canceled or highly reduced) due to the energy recovery that takes place in the second turbogroup ( 9).

Finally, referring to Figure 5, describes a device according to another preferred embodiment of the present invention in which a system for recovering the energy of recirculated gases with compressors in series is used as shown in Figure 3, which are driven by turbines in which they expand the gases evacuated to the atmosphere and the gases recirculated separately. The difference with respect to the embodiment shown in Figure 3 lies in the location of the ejector (7). In this case, the recirculated gases are initially expanded in the second turbine (8) of the second turbogroup (9). This second turbine (8) is of variable geometry to regulate the flow of recirculated gases. The mechanical energy produced in this expansion process is used in moving the second compressor (10) in charge of the first stage of fresh air compression in the intake system. In turn, the gases evacuated to the atmosphere expand in the first turbine (4) of the first turbogroup (5), which will be of variable geometry to force the flow of recirculated gases in the other branch. The mechanical energy generated in the first turbine (4) of the first turbogroup (5) is used to move the first compressor (20) in charge of the second stage of compression of the fresh air admitted by the engine.

Between both compression stages (between the second compressor (10) and the first compressor (20)) a heat exchanger (24) can be located. In this way, the compressed fresh air is directed to a third compression stage in the ejector (7) in which the recirculated gases expand once again completing their cooling. To improve the performance of this ejector (7), a variable geometry system can be included in the throat thereof. This preferential configuration guarantees the use of turbo machinery of reduced size, improving the transitory response, since the turbines transfer approximately half of the incoming flow to the engine and the compressors only transfer the fresh air, the first compressor (20) of the first turbogroup (5) being especially small for operating at high pressure. In this way a rapid transient response of the turbocharging system is guaranteed.

Another advantage of this preferred embodiment is associated with the absence of a condensate separator. In this case, since the mixture of fresh air and recirculated gases is made downstream of the compressors, no condensate separator is required, so that the absence of damage to said compressors is guaranteed. In this configuration the boost pressure of the engine would be very high when combining three flow compression processes in the intake line.

According to the foregoing, the present invention resolves several relevant aspects that differentiate it and give it clear advantages over the prior art:

- Cold combustion engines (RCCI or HCCI) require a large amount of recirculated gas. For this purpose, according to the present invention, recirculation is carried out from the high pressure zone of the motor to the low pressure zone. This difference in pressure is essential, since it allows to recirculate a large quantity of gases coming from the combustion and therefore have a lot of energy to recover.

- To reduce the formation of particulate matter and NOx in combustion, it is important that the recirculated gases are delivered to the engine as cold as possible. For this purpose, according to the present invention, the recirculated gases are cooled, for example, by the expansion of the gases in turbines and possible heat exchangers.

- In order to make the most of the energy of the gases coming from the combustion, it is necessary to "clean" these gases at the motor output (high pressure gases). For this, according to the present invention, it is essential that the gas post-treatment system is located before the bypass of the recirculated gases (pre-turbine location).

In short, the clean recirculated gases (taken after the post-treatment system) are combined with high pressure and their energy is recovered while cooling before carrying it to the entrance of the compression elements (for example ejector, compressors) located in the low pressure area of the engine intake. In this way, the present invention makes it possible to improve the oxidation conditions of the unburned hydrocarbons (HC), the CO and the particulate material present in the gases coming from combustion in internal combustion engines.

Among the advantages that the mentioned aspects confer to the present invention are the following:

- Allows the use of cold combustion engines with effective reductions of HC, CO, NOx and recirculated material.

- Allows the use of cold combustion engines with significant reductions in fuel consumption.

- Allows the use of cold combustion engines with an affordable cost of post-treatment of gases from combustion.

- Allows the use of cold combustion engines with conventional fuels without emissions of HC, CO, NOx and recirculated material.

Therefore, various preferred embodiments of the present invention for the recovery of energy in gases from the combustion of alternative internal combustion engines when they operate with specific combustion modes to reduce polluting emissions have been disclosed herein. of particulate matter and NOx, and specifically of gases recirculated to the admission whose energy is wasted according to the teachings of the prior art. These recirculated gases are very abundant in the specific combustion modes described, so that exploiting their energy by the present invention entails a more than notable advantage over the prior art.

For this, the various preferred embodiments of the present invention combine the specific location of the CO and HC post-treatment system, a particular definition of the supercharging system and the particular definition of the distribution of the exhaust and intake lines to optimize the energy recovery of the exhaust line, thus maximizing the reduction of consumption and polluting emissions.

In particular, various embodiments of a device for recovering energy from combustion gases in an internal combustion engine comprising, in a general manner, a first turbogroup, an ejector and an additional compressor that is part of the invention have been described in detail. a second turbogroup. However, the person skilled in the art will understand that the present invention is not limited to the specific embodiments described in detail, and that variations and modifications may be provided without departing from the scope defined by the appended claims.

Claims

1 Equipment for the recovery of energy from combustion gases in an internal combustion engine, the internal combustion engine comprising:

- a motor block (1); Y

- a post-treatment system (2) for gases from combustion;

characterized in that the energy recovery equipment is arranged downstream of the post-treatment system (2), and comprises:

- a first turbogroup (5) composed of a first turbine (4) and a first compressor (20) to recover energy from the gases evacuated to the atmosphere;

- an ejector (7) to recover energy from the recirculated gases; Y

- an additional compressor, which is a second compressor (10) forming a second turbogroup (9) together with a second turbine (8);

- the second turbine (8) of the second turbogroup (9), located in the line of recirculated gases between the exhaust line and the intake line, the recirculated gases expanding in said second turbine (8), allowing to obtain mechanical energy to drive to the second compressor (10) of the second turbogroup (9), in which the flow pressure of the intake line is increased;

so that the pressure of the gases of admission to the combustion engine is increased taking advantage of the gases coming from the combustion.

Equipment for recovering energy from combustion gases according to claim 1, characterized in that at least one of the first compressor (20) and the additional compressor is located downstream of the ejector (7), and the equipment also comprises a separator of condensed (23) located between the ejector (7) and the same.

Equipment for recovering energy from combustion gases according to claim 2, characterized in that the compressor located downstream of the ejector (7) is the additional compressor.

Equipment for recovering energy from combustion gases according to claim 2, characterized in that the compressor located downstream of the ejector (7) is the first compressor (20) of the first turbogroup (5).

Equipment for recovering energy from combustion gases according to claim 4, characterized in that the second compressor (10) of the second turbogroup (9) is located upstream of the ejector (7).

Equipment for recovering energy from combustion gases according to claim 4, characterized in that the second compressor (10) of the second turbogroup (9) is located downstream of the ejector (7), in parallel with respect to the first compressor ( 20) of the first turbogroup (5).

Equipment for recovering energy from combustion gases according to claim 1, characterized in that the second compressor (10) and the first compressor (20) are located in series upstream of the ejector

(7)

Equipment for recovering energy from combustion gases according to claim 7, characterized in that it also comprises a heat exchanger (24) between the second compressor (10) and the first compressor (20).

Equipment for recovering energy from combustion gases according to any of the preceding claims, characterized in that it also comprises at least one heat exchanger (21) downstream of the ejector (7).

10. Equipment for recovering energy from combustion gases according to claim 9, characterized in that the heat exchanger (21) is intercooler type.