DESC:FIELD OF INVENTION

The present invention relates to exhaust gas recirculation system in diesel engines. In particular, the present invention relates to the system for cooling the exhaust gases being recirculated in a diesel engine. More particularly, the present invention relates to the system for cooling exhaust gas recirculation to avoid condensation therein.

BACKGROUND OF THE INVENTION

Exhaust gas recirculation (EGR) is a technique used for reducing nitrogen oxide (NOx) emissions in internal combustion engines, particularly in petrol and diesel engines. As the name suggests, EGR technique is based on recirculating a portion of the exhaust gases of the engine back to the engine cylinders for diluting the O2 present in the incoming air stream.

This helps in providing gases inert to fuel combustion, which act as the combustion heat absorbers for reducing the peak in-cylinder temperatures. Normally, NOx is produced in a narrow range of high cylinder temperatures and pressures.

In a diesel engine, the exhaust gas replaces some of the excess oxygen present in the pre-combustion mixture. Since primarily NOx on subjecting the mixture of nitrogen and oxygen to high temperature, the lower combustion chamber temperature developed due to EGR reduces the amount of NOx the combustion generates (although with a loss of engine efficiency). Most modern engines now require exhaust gas recirculation to meet emissions standards.

So, in modern diesel engines, the EGR gas is cooled in a heat exchanger to allow the introduction of a greater mass of recirculated gas. Since diesel engines always operate with excess air, the possible high EGR rate up to 50% (with a large excess of air at engine idling) effectively controls NOx emissions.

A turbocharger, simply referred to as ‘Turbo’, is a turbine-driven forced induction device to increase the efficiency of an internal combustion engine and thereby, its power output by forcing extra air into the combustion chamber.

This is a significant improvement achieved over the output of a naturally aspirated engine due to the compressor being able to force more air and thus proportionately more fuel into the combustion chamber than when atmospheric pressure acts alone.

DISADVANTAGES WITH THE PRIOR ART

In turbocharged diesel engines, it is very important to control the inlet air temperature because of its direct influence on the exhaust gas temperature. In fact, if this temperature is very high, it may damage the expensive components disposed downstream the turbocharger.

Therefore, for preventing the EGR from increasing the inlet air temperature very high, EGR gas is made to pass through a cooler that removes a substantial amount of heat therefrom and transfers it to a coolant to lower the EGR gas temperature from as much as 5400C to 2600C or even lower.

However, it has been observed that over a period of time of engine being run in cold condition, condensation of water occurs in water/rapid cooled EGR cooler. This leads to the formation of lacquer, which causes EGR valve stickiness, which in turn results in failure of the engine within its warranty period in terms of the stringent emission norms.

DESCRIPTION OF THE PRESENT INVENTION

Convection is the movement of group of molecules within fluids and takes place through advection, diffusion or both. Convection cannot take place in solids because neither bulk current flows nor significant diffusion can take place in solids. Diffusion of heat can take place in solids, but that is referred to as heat conduction.
Convection is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it. Convection above a hot surface occurs because hot air expands, becomes less dense, and rises (Ideal Gas Law).

The heat transfer between a solid surface and a moving fluid is governed by the Newton’s Law of Cooling, which states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings. In other words, the heat transfer coefficient, which mediates between heat losses and temperature differences, is a constant and given by the equation:
q = hAs(Ts-T?);
wherein,
dconv = thermal energy (Joules),
h = heat transfer coefficient (W/(m2 K),
As = heat transfer surface area (m2),

T = temperature of the object's surface and interior
(assumed the same in this approximation), and

(Ts-T?) = time-dependent thermal gradient between the
environment and the object

The heat transfer coefficient h depends on the physical properties of the fluid and the physical situations in which convection occurs.

To increase the rate of heat transfer by convection:

• Increase the temperature difference (Ts-T?) between the surface and fluid;

• Increase the convection coefficient h;

This can be accomplished by increasing the fluid flow over surface, since h is a function of the flow velocity and a higher flow velocity leads to higher h value.
For example - Installing a pump or cooling fan, or replacing the existing pump/fan with larger capacity one.
• Increase the contact surface area As by attaching extended surfaces, e.g. fins to the surface.

For example - a heat sink with fins.

• Make the heat transfer surface of highly conductive materials, e.g. Aluminum.

Further, the convection cooling is achieved by two methods

(a) Forced Convection:
- Air is forced over the components with a fan or blower;
- The air velocity depends on the fan and local conditions.

(b) Natural or free Convection:
- The buoyancy effect (Density/Temp) forces hot air to flow to the top and cold air to come to the bottom. Typical velocity = 0.2 m/sec.

In accordance with the present invention, a steady and slow cooling avoids condensation or liquid formation on the EGR cooler and this in turn eliminates the EGR valve stickiness. With these relationships in mind, the EGR gas is cooled by using forced air received from the engine cooling fan. This configuration can easily be integrated or brought into the Turbocharged engines to cool down the compressed hot gas through a modular construction.

The equations for calculations of various parameters of heat conduction through fins are summarized below.

Extended Surface Heat Transfer Calculation:
P = Fin perimeter, L = Fin length,

Ac = Fin cross-sectional area, As = Fin surface area, and

qx = Heat content at fin cross-section at ‘x’ distance from cooler surface,

qx+dx = Heat content at fin cross-section at ‘x+dx’ distance from surface, and

dqconv = Heat conducted at the incremental fin cross-section ‘dx’ thick,

wherein, dAs is the surface area of the element, and
Energy balance is given by the equation:

Further,

if k, Ac are all constants.

Fin equation:

For fins having uniform cross-section in accordance with the present invention:

The above relationships resolve the various heat transfer relevant issues, e.g.:

- Size of Air-To-Air EGR Cooler required for specific diesel engines,
- Ease of manufacture,

- Integration into the existing layout of the EGR and Turbocharger systems,

- Testing with fan to achieve the desired effect during emission tests,

- Fin Effectiveness, and

- Fin Efficiency.

OBJECTS OF THE INVENTION

Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:

An object of the present invention is to provide a system for reducing condensation of water on EGR cooler in a diesel engine.

Another object of the present invention is to provide a system for reducing lacquer formation on the EGR valve in a diesel engine.

Still another object of the present invention is to provide a system for complying with the stringent the emission control standards in a diesel engine.

Yet another object of the present invention is to provide an integral and modular EGR cooler adapted to the existing diesel engine.

These and other objects and advantages of the present invention will become more apparent from the following description when read with the accompanying figures of drawing, which are, however, not intended to limit the scope of the present invention in any way.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided an air-to-air cooling system in EGR cooler for a diesel engine, comprising a modular EGR cooler having a plurality of fins and integrated with and disposed between the radiator cooling fan and the diesel engine, wherein hot exhaust gases entering from one end of the EGR cooler are substantially cooled within a range of 40 to 2000C in a steady and slow cooling by forced air received from the radiator cooling fan by avoiding condensation or liquid formation on the EGR cooler to eliminate EGR valve stickiness.

Typically, the forced air received from the radiator cooling fan are directed substantially perpendicular to the hot exhaust gases passing through the EGR cooler.

Typically, the EGR cooler is configured with a hollow body of profiled cross-section and preferably has a circular outer surface, more preferably a rectangular outer surface.

Typically, the plurality of fins passes through the hollow body of the EGR cooler in a predetermined pattern and protrudes out of the outer surface thereof as a function of the required engine architecture and packaging layout thereof.

Typically, the fins are configured with circular cross-section.

Typically, the fins are configured with rectangular, triangular, trapezoidal, concave, convex or parabolic cross-section.

Typically, the fins are configured with insulated tips to prevent heat transfer therethrough.

Typically, the hot exhaust gasses passing through the EGR cooler are cooled by a temperature of 40 to 500C, preferably by 450C.

Typically, the modular integrated EGR cooler comprises an elongated hollow body of profiled outer surface, preferably a rectangular outer surface disposed perpendicular to the forced air received from the radiator cooling fan for cooling the hot exhaust gases in a steady and slow cooling to avoid condensation or liquid formation on the EGR cooler to lower the peak combustion temperature in the engine.
Typically, the fins protrude out of the outer surface of the EGR cooler body in a predetermined pattern configured and optimized according to the required engine architecture and packaging layout thereof.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will be briefly described with respect to the accompanying drawings, which include:

Figure 1a shows a schematic flow of heat conducted through the extended surface of a typical EGR cooler formed in the shape of a fin for calculating the heat transfer therethrough.

Figure 1b shows an EGR cooler 10 having a typical fin 12 to be considered for detailed surface heat transfer calculations.

Figure 2 shows an existing arrangement of a turbocharged diesel engine equipped with an EGR cooler.

Figure 3 shows an integrated, modular EGR cooler configured with the modified fins provided in accordance with the present invention.

Figure 4 shows a first embodiment of the EGR cooler fins configuration in accordance with the present invention.

Figure 5 shows a second embodiment of the EGR cooler fins configuration in accordance with the present invention.

Figure 6a shows a third embodiment of the EGR cooler having a plurality of cylindrical fins configured in accordance with the present invention.

Figure 6b shows the CFD model at maximum EGR flow rate for the third embodiment of the EGR cooler shown in Fig. 6a.

Figure 7a shows a fourth embodiment of the EGR cooler configured in accordance with the present invention and having a plurality of cylindrical fins.

Figure 7b shows the CFD model at maximum EGR flow rate for the fourth embodiment of the EGR cooler shown in Fig. 7a.

Figure 8 shows a CFD model of the EGR cooler configured in accordance with the present invention and having a circular surface (Figure 6a) for cooling the exhaust gases to be recirculated.

Figure 9 shows a graphical representation of the EGR cooling by depicting the EGR gas temperature versus engine speed captured for the EGR cooler inlet against the EGR cooler outlet for the conventional EGR as well as EGR cooler for the EGR configured in accordance with the present invention.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In the following, different embodiments of the present invention will be described in more details with respect to the accompanying drawings without limiting the scope and ambit of the present invention in any way.

Figure 1a shows a schematic flow of heat conducted through the extended surface of a typical EGR cooler formed in the shape of a fin for calculating the heat transfer therethrough. EGR cooler body has a surface temperature Tb and a pin type cooler fin protruding therefrom in ‘x’ direction. The fin has a perimeter P(pd), length b, cross-sectional area Ac, surface area As, and an incremental disc of thickness dx for heat conduction calculations. At a fin cross-section disposed at a distance ‘x’ away from the EGR cooler body surface, qx is the heat content and at fin cross-section disposed at a distance ‘x+dx’ away from the EGR cooler surface, qx+dx is the heat content at fin cross-section disposed at a distance ‘x+dx’ away from the EGR cooler surface and dqconv is the heat conducted at this incremental fin cross-section and which is the difference of the qx and qx+dx.

Figure 1b shows an EGR cooler surface 10 having a typical fin 12 to be considered for detailed calculations for surface heat transfer thereof. Here, the EGR cooler body surface is at a temperature Tb and T8 is the air temperature. This pin type cooler fin protruding from the EGR cooler surface 10 has a diameter d and length b. The heat is conducted from the EGR cooler surface 10 as well as fins 12 to the surrounding air for cooling the exhaust gases to be recirculated. Here, the thermal conductivity of fins is k [Watt/(m.K)] and h is the heat transfer coefficient [Watt/(m2.K)] of the fin material.

Figure 2 shows an existing arrangement of a turbocharged diesel engine 02 equipped with a radiator cooling fan 04 and a conventional EGR cooler and water circuit 06.

Figure 3 shows a modular EGR cooler 108 integrated with a radiator cooling fan 04 and having rectangular surface 110 configured with fins 112 modified in accordance with the present invention. Hot exhaust gases 14 from the exhaust manifold or turbocharger are recirculated to the EGR cooler 108 from one end thereof and cooled EGR gases are supplied in a steady and slow cooling by means of radiator fan air flow to avoid any condensation or liquid formation on the EGR cooler 108 to eliminate any possible EGR valve stickiness. Accordingly, hot EGR gas 14 is cooled by using forced air received from the radiator cooling fan and the cooled EGR gas 16 is supplied to the engine cylinders to lower the peak combustion temperature. This configuration can easily be integrated or brought into turbocharged diesel engines through a modular construction.

Figure 4 shows a first embodiment of the EGR cooler 108 with a cylindrical outer surface 110 having a plurality of fins 112 configured in accordance with the present invention and passing therethrough to protruding out of the cylindrical outer surface 110 of the EGR cooler 108 in a predefined pattern. As already described in respect of Figure 3, the hot exhaust gases 114 from the exhaust manifold or turbocharger are recirculated to the EGR cooler 108 from one end thereof and EGR gases 116 cooled by means of radiator fan air flow exit from the other end 116 to avoid any condensation or liquid formation on the EGR cooler 108.

Figure 5 shows a second embodiment of the EGR cooler 208 with a rectangular outer surface 210 and having a plurality of fins 212 configured in accordance with the present invention and passing therethrough to protrude out of the rectangular outer surface 210 of the EGR cooler 208. The hot exhaust gases 214 from the exhaust manifold or turbocharger are recirculated to the EGR cooler 208 from one end thereof and EGR gases 216 cooled by means of fan air flow 220 and exiting from the other end thereof are supplied in a steady and slow cooling from the other end 216 to avoid any condensation or liquid formation on the EGR cooler 208 to eliminate any possible the EGR valve stickiness.

Figure 6a shows a third embodiment of the EGR cooler 308 with circular outer surface configured in accordance with the present invention and having a plurality of cylindrical tubes 312 connected between two end plates 3006, 3008 of the EGR cooler 308 which are holding the side chambers 3010, 3012. The hot exhaust gases 314 from the exhaust manifold or turbocharger are recirculated to the EGR cooler 308 from one end plate 3006 thereof and EGR gases 316 cooled by means of fan air flow and exiting from the other end plate 3008 thereof are supplied to provide steady and slow cooling to avoid condensation or liquid formation on EGR cooler 308 for eliminating any EGR valve stickiness.

The following table depicts the EGR inlet and outlet temperatures at different engine speeds:

Engine Speed (rpm) EGR Cooler Inlet Temperature (0C) EGR Cooler Outlet Temperature (0C)
1000 207.8 50
1400 389.2 190.6
2600 454.9 238.94

Figure 6b shows the CFD model for the temperature gradient profile for the third embodiment of the EGR cooler 308 shown in Figure 6a.

Figure 7a shows a fourth embodiment of the EGR cooler 408 with rectangular outer surface configured in accordance with the present invention and having a plurality of circular tubes 412 passing through the rectangular fins 418 and connected between two end chambers 4006, 4008 of the EGR cooler 408. The hot exhaust gases 414 from the exhaust manifold or turbocharger are recirculated to the EGR cooler 408 from one end chamber 4006 thereof and EGR gases 416 cooled by means of fan air flow and exiting from the other end chamber 4008 thereof are supplied to provide steady and slow cooling to avoid condensation or liquid formation on EGR cooler 408 for eliminating any EGR valve stickiness.

The following table depicts the EGR inlet and outlet temperatures at different engine speeds:

Engine Speed (rpm) EGR Cooler Inlet Temperature (0C) EGR Cooler Outlet Temperature (0C)
1000 207.8 50.02
1400 389.2 164.7
2600 454.9 203.9

Figure 7b shows the CFD model for the temperature gradient profile for the fourth embodiment of the EGR cooler 308 shown in Figure 7a considered at 2100 rpm. On comparing the third and fourth embodiments shown in Figures 6a and 7a, it is clear that the rectangular cross-section of Figure 7a demonstrates its cooling enhanced by about 450C with respect to the circular outer surface of Figure 6a.

Accordingly, different fin shapes can be experimented in accordance with the idea underlying the present invention involving air to air EGR cooling arrangement based on the desired engine architecture and the layout package requirements.

Figure 8 shows CFD model of the EGR cooler configured in accordance with the present invention and having a circular surface 10 (Figure 6a) for cooling the exhaust gases to be recirculated and depicting the EGR inlet 14, EGR outlet 14 as well as inlet air 102 and outlet air 104 for cooling the exhaust gases to be recirculated.

Figure 9 shows a graphical representation of the EGR cooling by depicting the EGR gas temperature versus engine speed captured for the EGR cooler inlet against the EGR cooler outlet for the EGR cooler with a circular outer surface (Figure 6a) as well as EGR cooler with a rectangular outer surface (Figure 7a) configured in accordance with the present invention. The occurrence of a substantial EGR cooling of the order of about 450C can be seen from this graph for the EGR configuration according to the present invention.

In accordance with the present invention, it is assumed that uniform flow velocity exists in front of the EGR cooler. Further, the boundary conditions at air inlet temperature = 500C, i.e. air flow velocity used, EGR flow rate and temperature are tabulated below:

Engine Speed (rpm) Air velocity (m/sec) EGR flow rate (kg/hr) EGR Temperature (0C)
1000 2 0.46 207.8
1400 3.1 11.19 389.2
2600 6.47 15.73 454.9

The properties of the material involved herein are as under:

Sr. No. Properties Air / EGR Steel
1 Density (kg/m3) Ideal Gas 8030
2 Specific Heat (J/kg-K) 1006 502
3 Thermal Conductivity (W/m-K) 0.0242 16

It is to be noted that although the present invention is exemplarily described with regard to the cylindrical pin type of fins protruding away from the outer surface of the EGR cooler, these fins can be configured in any other possible shapes, e.g. rectangular, triangular, trapezoidal, concave, convex, parabolic etc. Moreover, the convection heat transfer may take place over the entire surface thereof.

Alternatively, the tip can be made insulated and therefore no heat transfer takes place through the insulated tips of the fins in this case. The EGR input conditions are as given below:

Sr. No. Engine (rpm) Mass Flow Rate (kg/hr) Temperature (0C)
1 2600 15.73 454.9
2 1400 11.19 389.2
3 1000 0.46 207.8

The following table includes the results of the computational fluid dynamics data (CFD) of the forced air velocity before the EGR cooler:

Air Flow Data (m/sec)
Sr. No. Speed (rpm)
HI 2600 1400 1000
1 7 6.6 2.8 1.7
2 9.1 6.9 3.4 1.9
3 6.5 5.9 2.6 1.7
4 5.7 5.1 2.3 1.6
5 6.4 5.4 2.6 1.6
6 6.1 5.4 2.1 1.6
7 6.1 5.2 2.3 1.6
8 6.5 6.2 2.9 1.4
9 8.4 6.8 3.3 2.1
10 8.7 7.7 3.7 2.3
11 6.9 6 2.8 2.1
12 8.1 7.5 3.5 2.3
13 7 6.9 3.4 2.2
14 8.2 7.5 3.6 2.5
15 7.4 6.7 3.2 2.1
16 9 8.2 3.7 2.3
17 7.1 5 2.9 2.2
18 8.3 7 3.5 2.2
19 8.4 7.2 3.6 2.2
20 8.3 6.9 3.5 2.3
21 7.1 5.8 3.5 1.9
Average 7.44 6.47 3.1 2

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

Air-To-Air cooling system for EGR cooler in a diesel engine, which is configured in accordance with the present invention has the following advantages:

• Avoids water condensation, thus no lacquering.

• Cost-effective solution.

• Simple engine layout for EGR Engine.

• No servicing required.

• Economic to operate.

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE

Air-To-Air cooling system for EGR cooler in a diesel engine configured in accordance with the present invention has the following technical and economic advantages:

The exemplary embodiments described in this specification are intended merely to provide an understanding of various manners in which this embodiment may be used and to further enable the skilled person in the relevant art to practice this invention. The description provided herein is purely by way of example and illustration.

Although, the embodiments presented in this disclosure have been described in terms of its preferred embodiments, the skilled person in the art would readily recognize that these embodiments can be applied with modifications possible within the spirit and scope of the present invention as described in this specification by making innumerable changes, variations, modifications, alterations and/or integrations in terms of materials and method used to configure, manufacture and assemble various constituents, components, subassemblies and assemblies, in terms of their size, shapes, orientations and interrelationships without departing from the scope and spirit of the present invention.

While considerable emphasis has been placed on the specific features of the preferred embodiment described here, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiments without departing from the principles of the invention.

These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

Many of the fastening, connection, processes and other means and components utilized in this invention are widely known and used in the field of the invention described, and their exact nature or type is not necessary for an understanding and use of the invention by a person skilled in the art and they will not therefore be discussed in significant detail.

The numerical values given of various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher or lower than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the disclosure unless there is a statement in the specification to the contrary.

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.

The use of the expression “a”, “at least” or “at least one” shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention.

Also, any reference herein to the terms ‘left’ or ‘right, ‘up’ or ‘down, or ‘top’ or ‘bottom’ are used as a matter of mere convenience, and are determined by standing at the rear of the machine facing in its normal direction of travel.

Furthermore, the various components shown or described herein for any specific application of this invention can be widely known or used in the art by persons skilled in the art and each will likewise not therefore be discussed in significant detail. When referring to the figures, like parts are numbered the same in all of the figures. ,CLAIMS:We claim:

1. An air-to-air cooling system in EGR cooler for a diesel engine, comprising a modular EGR cooler having a plurality of fins and integrated with and disposed between the radiator cooling fan and the diesel engine, wherein hot exhaust gases entering from one end of the EGR cooler are substantially cooled within a range of 40 to 2000C in a steady and slow cooling by forced air received from the radiator cooling fan by avoiding condensation or liquid formation on the EGR cooler to eliminate EGR valve stickiness.

2. Cooling system as claimed in claim 1, wherein the forced air received from the radiator cooling fan are directed substantially perpendicular to the hot exhaust gases passing through the EGR cooler.

3. Cooling system as claimed in claim 2, wherein the EGR cooler is configured with a hollow body of profiled cross-section and preferably has a circular outer surface, more preferably a rectangular outer surface.

4. Cooling system as claimed in claim 3, wherein the plurality of fins passes through the hollow body of the EGR cooler in a predetermined pattern and protrudes out of the outer surface thereof as a function of the required engine architecture and packaging layout thereof.

5. Cooling system as claimed in claim 4, wherein the fins are configured with circular cross-section.

6. Cooling system as claimed in claim 4, wherein the fins are configured with rectangular, triangular, trapezoidal, concave, convex or parabolic cross-section.

7. Cooling system as claimed in anyone of the claims 1 to 6, wherein the fins are configured with insulated tips to prevent heat transfer therethrough.

8. Cooling system as claimed in anyone of the claims 1 to 7, wherein the hot exhaust gasses passing through the EGR cooler are cooled by a temperature of 40 to 500C, preferably by 450C.
9. Cooling system as claimed in anyone of the claims 1 to 8, wherein the modular integrated EGR cooler comprises an elongated hollow body of profiled outer surface, preferably a rectangular outer surface disposed perpendicular to the forced air received from the radiator cooling fan for cooling the hot exhaust gases in a steady and slow cooling to avoid condensation or liquid formation on the EGR cooler to lower the peak combustion temperature in the engine.

10. Cooling system as claimed in claim 4, wherein the fins protrude out of the outer surface of the EGR cooler body in a predetermined pattern configured and optimized according to the required engine architecture and packaging layout thereof.

Dated: this day of 22nd November 2016. SANJAY KESHARWANI
APPLICANT’S PATENT AGENT