EXHAUST GAS RECIRCULATION DEVICE

Field of the Invention

The invention relates to an exhaust gas recirculation device for an exhaust gas recirculation system (EGR system) of an internal combustion engine. The invention particularly relates to an EGR device that attenuates the pulsations existing in exhaust gas inflow and enhances the mixing of the exhaust gas with the intake air to help reduction of harmful exhaust emissions.

Background of the Invention

In order to achieve better performance coupled with fuel economy, automobiles have slowly moved from using petrol engines to diesel engines. Both engines have advantages and disadvantages over each other. But there have been huge developments of new technology accessories fitting on diesel engines to limit its shortfalls. One such technology used in diesel engines is the exhaust gas recirculation system.

Exhaust gas recirculation system (EGR system) is employed in diesel engines for reducing the amount of nitrogen oxides produced after combustion to acceptable level as per legislative norms. The EGR system reduces NOx by recirculating small amount of exhaust gas into the intake manifold where it mixes with charge air. NOx is basically produced during the periods of combustion when the combustion temperature exceeds to about 2500°F. Diluting the incoming air with small quantity of exhaust gas raises the specific heat capacity of the A/F mixture thus helps in reducing the peak combustion temperature and pressure. Reduction in combustion temperature causes reduction in NOx production. The essence of EGR

system greatly depends on the amount of EG recirculated. Increasing the amount of exhaust gas, though, causes reduction in combustion temperature and NOx emissions but also, above certain level, results in increase in PM emissions. Moreover, present EGR systems without any mixer are sensitive to even small changes in the geometric configuration leading to EGR unequal distribution from cylinder to cylinder and imperfect mixing of air and EGR. Such an unequal distribution can lead to higher NOx and PM emissions. Thus, it becomes necessary to make proper geometrical changes in EGR system to obtain nearly equal cylinder to cylinder EG distribution. Most of the present EGR systems do not employ mixer to facilitate thorough mixing of exhaust gas with air due to the pressure drop caused by mixer, which may render no EGR flow.

Exhaust gas recirculation systems (EGR systems) work by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The portion of the exhaust gas is introduced from an exhaust pipe into fresh intake air of an intake pipe so that the exhaust gas and fresh intake air is mixed and supplied into the combustion chamber of the internal combustion engine. This reduces the harmful emission of toxic gases such as nitrogen oxide (NOx). The EGR system recirculates the exhaust into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. These gases displace some of the normal intake charge. This chemically slows and cools the combustion process, thus reducing NOx formation.

An EGR system of the above-mentioned type is already known, which provides for centric feeding of the exhaust gas into the intake air line. In this, the exhaust gas enters centrically in relation to the intake airflow and in the same direction of flow. However, mixing between exhaust gas flow

and intake airflow occurs only in the marginal areas, depending on the relative speed of exhaust gas and intake air. Mixing of the exhaust gases fed in over the short distance between admission point and charge air distributor is poor leading to unequal distribution of exhaust gas into the cylinders.

German patent document DE 43 19 380 C2 discloses an EGR device for an IC engine with an exhaust turbocharger, with an inlet system, a charge air line, an exhaust system, a return line for an exhaust gas component flow, together with a jet diffuser unit to which charge air is admitted and into which the return line also opens, the jet diffuser unit being arranged directly in the charge air line and the jet diffuser unit, when suitably designed, produces an equilibrium of the pressure differentials between exhaust and inlet system, so that an exhaust gas component flow can be added to the compressed charge air through the return line opening into the jet diffuser unit in the area of cross-sectional constriction and thereby fed into the inlet system. Optimum mixing of intake air and exhaust gas is not guaranteed, however, because the exhaust gas flows in the marginal area and there is no further additionally generated swirl or turbulence to promote further mixing of the two gas flows.

FR publication no. 2 896 546 discloses an EGR device that sufficiently introduces exhaust gas into fresh intake air. According to the device of this prior art, an intake air pipe is divided into two parts and an annular space or opening is formed between the two pipes. The annular space or opening is covered by a housing into which exhaust gas is supplied through a pipe, so that sufficient amount of exhaust gas may be re-circulated. According to this prior art, since the exhaust gas directly flows into the intake air pipe through the annular space it may be difficult to equally mix the exhaust gas

with the fresh intake air without deviation. It may be furthermore difficult to sufficiently mix the exhaust gas with the fresh intake air, depending on the amount of the exhaust gas to be recirculated.

Further, in conventional EGR systems the exhaust gas flows into the charge air pipe intermittently or in a pulsating manner (not continuously) at lower engine speeds. The two fluids, i.e. air and exhaust gas do not mix thoroughly by the time they reach the intake manifold plenum, which leads to unequal distribution of exhaust gas to the cylinders. This results in combustion that renders higher hazardous emissions. Also, due to different operating conditions of the engine, different patterns of air and exhaust gas inflow exists. At lower engine speeds the air and exhaust gas inflows are observed to be highly pulsating which renders non-uniform mixture inside the manifold plenum during individual suctions by the cylinders. So, as long as such inflow pulsations exist, no matter how much travel distance is available, the system is bound to circulate unequal mass fractions into cylinders depending upon their time of suction. Previously known devices such as rotating blade mixers, helical static mixers help in mixing the two fluids at the cost of considerable amount of pressure drop and also involve manufacturing difficulties, thus increasing the cost of manufacturing. These mixers can only mix two fluids but do note reduce inflow pulsations whenever required. Thus, an additional system/device such as buffer tank is needed, which would require additional cost for manufacturing.

Object of the Invention

It is therefore an object of the invention to provide an EGR system that attenuates the pulsations existing in the exhaust gas flow to nullify its effect

at the outlet and to enhance the mixing of the exhaust gas with intake air to further reduce the exhaust emissions beyond the current level.

It is also the object of the invention to avoid non-uniform mixture inside the manifold plenum during individual suctions by the cylinders

Summary of the Invention

In order to achieve the above object, this invention provides an exhaust gas recirculation device (EGR device) having a swirl chamber having provisions for at least two inlets. The first inlet allows entry of the exhaust gas routed from the exhaust line and the second inlet allows entry of air from the air intake system in the same direction of flow as of the exhaust gas creating a swirling mix of the exhaust gas and the air in the same direction within the swirl chamber. The swirling mixture of the exhaust gas and the air exits the swirl chamber axially, thereby further transmitting the swirl effect of the mixture thus further enhancing the mixing of the exhaust gas and the air before reaching an intake manifold plenum.

In a preferred embodiment the exhaust gas flows into the swirl chamber in a tangential direction through a first inlet pipe, and, similarly, the fresh air inflow flows into the swirl chamber in a tangential direction through the second inlet pipe in the same direction of flow of the exhaust gas.

In a preferred embodiment, the swirl chamber is a cylindrical disc to which at least two inlets are attached.

In a preferred embodiment, the diameter of the swirl chamber is at least greater than two times the diameter of the larger of the two inlets.

In an optional embodiment, the depth of the swirl chamber may be varied.
The invention, therefore, provides enhanced mixing of the exhaust gas and air and also reducing the pulsations of the exhaust gas from being visible at the exit. Thus, at any operating condition of the engine, the present invention enables introduction of uniform mixture into the intake manifold plenum.

Accordingly, the invention relates to an exhaust gas recirculating device comprising: a swirl chamber; a first inlet adapted to allow exhaust gas to flow into the swirl chamber; a second inlet adapted to allow fresh air inflow to flow into the swirl chamber in the same direction of flow as the exhaust gas, such that the mixture of the exhaust gas and fresh air inflow are caused to swirl in a single direction and exit the swirl chamber axially through an outlet.

Brief Description of the Drawings

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same,
Figure 1(a) shows a general layout of an engine system including an exhaust gas recirculation system;

Figure 1 (b) shows a partial view of the engine system incorporating the exhaust gas recirculating system according to the present invention;
Figure 2 shows the exhaust gas recirculating device according to the present invention;

Figure 3(a) - 3(d) shows the preferred variations in the internal chamber of the exhaust gas recirculating device of the present invention;
Figure 4 shows a variation of the exhaust gas recirculation device according to an embodiment of the invention;

Figure 5 (a) - 5(g) shows the different constructions of the exhaust gas recirculating device of the present invention;

Figure 6 shows the amplitude of fluctuations in the exhaust gas inflow and outflow according to the present invention.
Figure 7 shows the port-to-port distribution of mass fraction with and without the exhaust gas recirculating device.

Detailed Description of the Invention

Referring to figure 1(a), an engine system comprises an intake manifold (20) and an exhaust manifold (40). Exhaust gas is carried from the exhaust line to the intake side through an exhaust gas recirculation system (EGR). The dotted lines in figure 1(a) represent the EGR system of an engine (E). The exhaust gas is carried through a pipe (P) attached to the exhaust system upstream of a turbocharger (22) and it delivers the exhaust gas into the fresh charge air downstream of a charge air cooler (25) just before the plenum (20). The EGR system consists of an EGR control valve (28) to control the amount of exhaust gas recirculated and a cooler (29) to cool the recirculated hot exhaust gas before entering into the combustion chamber.

The exhaust gas recirculation (EGR) device according to the invention is situated at a suitable location on the engine (E) as shown in figure 1(b). The construction and function of the EGR device according to this invention will be explained in the following paragraphs.

The EGR device (50) according to the present invention, as illustrated in figure 2, comprises a swirl chamber (10) capable of being provided with at least two inlets (2, 4). A first inlet (2) is adapted to allow exhaust gas from the exhaust manifold to enter into the swirl chamber (10). The first inlet (2) is connected to the swirl chamber (10) through a first inlet pipe (3) having a diameter D1. A second inlet (4) is adapted to allow air inflow to enter into the swirl chamber (10) in the same direction of flow of the exhaust gas. The second inlet (4) is connected to the swirl chamber (10) through a second inlet pipe (5) having a diameter D2. Preferably, the exhaust gas is forced to enter into the swirl chamber (10) in a tangential direction through the first inlet pipe (3), and, similarly, the air inflow is forced to enter the swirl chamber (10) in a tangential direction through the second inlet pipe (5). The exhaust gas and the air entering into the swirl chamber in the same phase through their respective inlets mix well with each other and are caused to swirl together in the direction (8) indicated by broken arrows in figure 1. The swirl is normally created utilizing the flow momentum of both the exhaust gas and the air in proportion to their respective flow pressure.

The swirling mixture of the exhaust gas and the air is adapted to axially exit the swirl chamber through an outlet (6), thus further transmitting the swirl effect to additionally enhance the mixing of these fluids before reaching the intake manifold plenum. The majority of the mixing is achieved within the swirl chamber (10) itself and is further augmented

through the distance the mixture of the two fluids travels before reaching the manifold plenum. This configuration ensures larger swirl and greater mixing independent of the axial distance to be travelled before reaching the intake manifold plenum. Each of these fluids (exhaust gas and fresh air) enters into the swirl chamber (10) in a pulsating manner, but exit the swirl chamber uniformly with reduced pulsations. As there exists a thorough mixture in the manifold plenum, every cylinder of the engine receives uniform mixture independent of flow pulsations.

All the systems available downstream of the swirl chamber (i.e. after the exit from the swirl chamber) perform efficiently towards harmful emissions reduction independent of the upstream (i.e. before the swirl chamber) flow pulsations. The exhaust gas and the air mix thoroughly with each other so that the mixture, as a single fluid, enters into the further systems, thus rendering efficient performance. The invention serves a dual purpose of thorough mixing and reducing the fluctuation or pulsation of inflow inside the swirl chamber (10), which acts like a buffer storage.

In a particular embodiment, the swirl chamber (10) is a cylindrical disc whose diameter is greater than at least two times the diameter of the larger of the two inlet pipes (3, 5). This would enable the centre of the swirl to be closer to the centre of the swirl chamber (10) for effective mixing inside the swirl chamber (10) and to enable buffering action.

In an alternate embodiment, the swirl inside the swirl chamber (10) can be further augmented by providing swirl intensifying plate elements inside the chamber (10). Figure 3(a) shows such a swirl intensifying plate element in the form of a helical twisted element (12) provided inside the swirl chamber (10) on which pipes (3, 5) are attached tangentially. Figure 3(b) illustrates

another swirl intensifying plate element in the form of rotating blades (13) used inside the swirl chamber on which pipes (3, 5) are attached tangentially.

Figure 3(c) illustrates the helical twisted element (12) used inside a swirl chamber where the pipes (3, 5) are attached non-tangentially to the swirl chamber (10). Figure 3(d) illustrates the rotating blades (13) used inside the swirl chamber (10) where the pipes (3, 5) are attached non-tangentially to the swirl chamber (10).

Figure 4 shows a variation of the construction of the EGR device (50). The first inlet pipe (3) and the second inlet pipe (5) are located substantially perpendicular to each other on the swirl chamber. However, the fresh air inflow flowing through the second inlet pipe (5) would still flow in the same direction of flow of the exhaust gas that enters the swirl chamber through first inlet pipe (3). This initiates the mixing and swirling flow of the exhaust gas and the fresh air inflow inside the swirl chamber (10).

The depth of the swirl chamber (10) depends on the diameter of the larger of the two intake pipes. In the EGR device according to the present invention the larger pipe is the second inlet pipe (5) that allows the flow of the fresh air inflow. The minimum depth of the swirl chamber (10) is substantially equal to the diameter of the second inlet pipe (5) and the maximum depth of the swirl chamber (10) is about 1.5 times the diameter of the second inlet pipe (5). It is to be understood that the range specified above is for obtaining significantly better performance of the EGR system. However, the dimensions can be changed below the minimum and above maximum limits as per the available packaging space and possible

orientation of the engine, thereby having a trade off between performance and packaging possibilities.

The diameter of the first inlet pipe (3) and the second inlet pipe (5) can be varied taking into consideration that the diameter of the swirl chamber is preferably greater than 2 times the diameter of the second inlet pipe (5).
In a preferred embodiment, the profile of the swirl chamber (10) and the first and second inlet pipes (3, 5) can be varied. As shown in figure 5(a) the swirl chamber (10) may be tapered inwardly toward the outlet (6). Such a profile would enhance the swirling and mixing of the exhaust gas and the air inflow as it exits the chamber (10) through outlet (6).

Alternatively, the swirl chamber (10) may be funnel shaped as illustrated in figure 5(b). In another preferred variation, the swirl chamber (10) may be profiled to be hemispherical or spherical in shape, as illustrated in figure 5(c) and 5(d) respectively. In a further preferred variation, the first inlet pipe (3) or the second inlet pipe (5) may be tapered toward the entry into the swirl chamber (10). Figure 5(e) shows a swirl chamber (10) and the second inlet pipe (5) being formed with a taper.

Alternatively, the first and second inlet pipes (3, 5) may be attached to the swirl chamber (10) with a slight non-tangency as illustrated in figure 5(f). Figure 5(g) illustrates a non-circular swirl chamber (10) with circular or non-circular axial outlet (6)

In a further preferred embodiment, the EGR device may be formed with a combination of any of the features illustrated in figures 5(a) to 5(g).

The EGR device described in the preceding paragraphs can be retrofitted in an existing engine of an automobile. Alternately, the EGR device can be made as an integral unit with the intake manifold plenum of the engine or integral unit with one of the intake pipes. The first and second inlet pipes (3, 5) may be suitably connected to the swirl chamber (10) by welding or other suitable process.

The invention described above utilizes a hollow swirl chamber (10), which has a size greater than the first and second inlet pipe (3, 5). At certain engine speeds, it is found that the exhaust gas inflow fluctuates, as illustrated in the thick continuous line shown in Figure 6. The amplitude of the fluctuation of the exhaust gas flow is indicated by the letter 'E' in figure 6. Due to such fluctuations, there exist distinct instances of higher and lower amount of exhaust gases entering the swirl chamber (10). The entry of the exhaust gas into the plenum and subsequently into the combustion chamber is desired to be uniform for equal performance by each cylinder. Due to the larger size of the swirl chamber (10), it also serves the function of a buffer tank in which excess amount of exhaust gas is stored (for instance, during the instance of smaller amount of exhaust gas entry) ensuring the uniform recirculated exhaust gas flow to the plenum and combustion chambers as desired by the combustion chambers.

Figure 7 shows quantitatively the distribution of mass fraction of the exhaust gas entering into each cylinder port. It can be clearly seen that the mass fractions of both the fluids entering into individual ports are nearly equal.

In the absence of a swirl chamber, it has been found that the exhaust gas flows into the plenum with considerable amplitude of fluctuations as shown

in figure 6 denoted by 'E' causing varying amount of exhaust gas entry the cylinders in the combustion chambers. The amplitude of fluctuation in the mixture outflow in the absence of a swirl chamber is shown as a dotted line and is denoted by 'N' in figure 6. The amplitude of fluctuation in the mixture outflow in the presence of the swirl chamber of the EGR of the present invention is shown by the thin continuous line and is denoted by 'M' in figure 6. It is obvious to note the reduction in the inflow pulsation of the fluids entering the EGR system according to the present invention. The inflow pulsations are reduced due to at least the size of the swirl chamber being large enough to act as a buffer storage tank.

While the above paragraphs explain the various embodiments of the invention, it is apparent that numerous modifications and variations can be made without departing from the scope and spirit of this invention. It is therefore intended that this invention be limited only as indicated in the appended claims.

1. An exhaust gas recirculating device comprising:

a swirl chamber (10);

a first inlet (2) adapted to allow exhaust gas to flow into the swirl chamber (10);
a second inlet (4) adapted to allow fresh air inflow to flow into the swirl chamber (10) in the same direction of flow as the exhaust gas,

such that the mixture of the exhaust gas and fresh air inflow creates a swirl inside the swirl chamber (10) in a single direction and exits the swirl chamber (10) axially.

2. The exhaust gas recirculation device as claimed in claim 1, wherein the first inlet (2) is positioned on the swirl chamber (10) such that the exhaust gas flows tangentially into the swirl chamber (10).

3. The exhaust gas recirculation device as claimed in claim 1 or 2, wherein the second inlet (4) is positioned on the swirl chamber (10) such that the fresh air flows tangentially into the swirl chamber (10).

4. The exhaust gas recirculation device as claimed in claim 3, wherein the first inlet (2) and the second inlet (4) are positioned on the swirl chamber substantially perpendicular to each other.

5. The exhaust gas recirculation device as claimed in claim 1, wherein the first inlet (2) and the second inlet (4) are connected to the swirl chamber through a first inlet pipe (3) and a second inlet pipe (5) respectively.
6.

6. The exhaust gas recirculation device as claimed in claim 1, wherein the swirl chamber (10) is a cylindrical disc whose diameter is greater than at least two times the diameter of the larger of the two inlet pipes (3, 5).

7. The exhaust gas recirculation device as claimed in claim 1, wherein swirl intensifying plate elements are provided inside the chamber (10).

8. The exhaust gas recirculation device as claimed in claim 5, wherein the depth of the swirl chamber is about 1 to 1.5 times the diameter of the second inlet pipe (5)

9. The exhaust gas recirculation device as claimed in claim 1, wherein the profile of the swirl chamber may be either tapered, funnel-shaped, hemispherical, spherical or any combination thereof.

10. The exhaust gas recirculation device as claimed in claim 5, wherein
the first inlet pipe (3) and/or the second inlet pipe (5) may be tapered
toward the entry into the swirl chamber (10).

11 The exhaust gas recirculation device as claimed in claim 1, wherein the swirl chamber (10) is capable of storing excess amount of exhaust gas.

12. The exhaust gas recirculating device as claimed in any one of the preceding claims, wherein the device is capable of being retrofitted onto an intake manifold plenum.

13. An exhaust gas recirculation system comprising the exhaust gas recirculating device as claimed in any one of the preceding claims.

14. An automobile engine comprising the exhaust gas recirculating system as claimed in claim 13.