A SYSTEM FOR COOLING AND CIRCULATING EXHAUST GAS

FIELD OF INVENTION

The present invention generally relates to an Exhaust Gas Re-circulation (EGR) system and particularly to a system for cooling and circulating exhaust gas in an internal combustion engine with low pressure fuel injection system.

BACKGROUND OF INVENTION

Currently, cooled exhaust gas recirculation (EGR) systems are used in the IC engines of the motor vehicle for meeting exhaust gas emission regulations, i.e. for reducing nitrogen oxide emissions (NOx). It is necessary to maintain emission level of the oxides of nitrogen pollutants within legal limitations and regulations of emission norms. Such EGR systems receive and cool the exhaust gas from the IC engine and re-circulate the exhaust gas mixed together with charged air, again to the IC engine. The re-circulated exhaust gas to the IC engine reduces the oxygen content corresponding to the quantity and consequently the maximum gas temperature during combustion is held at an optimum level by not exceeding the oxides of nitrogen pollutants beyond the legal limits.

FIGS. 1 & 2 illustrate a schematic diagram of conventional low pressure and high pressure EGR systems for a turbocharged IC engine, respectively, in accordance with a prior art. The EGR systems are classified by means of introduction of the exhaust gas by an external arrangement or by an internal in-built arrangement on the engine. The external EGR systems are further classified by the location of mixing point of exhaust gas and charged air, by which it is refereed as high pressure EGR cooling system and low-pressure EGR cooling system. If the exhaust gas is introduced before a turbocharger, then the EGR systems are referred as low-pressure EGR systems whereas, if the exhaust gas is introduced after the turbocharger, the EGR systems are referred as high-pressure EGR systems. In case of naturally aspirated engines, the low-pressure EGR systems are only applicable. The conventional EGR systems are associated with an engine 101 having an intake manifold (102), an exhaust manifold (103) and a fan (104).

In case of conventional low pressure EGR system as shown in FIG. 1, the exhaust gas from the exhaust manifold (103) is carried to a turbine (105) for driving a compressor 110 of the turbocharger. Then, the exhaust gas is passed to an EGR cooler (108) through a catalyst 106 and an EGR valve (107) for cooling the exhaust gas. The cooled exhaust gas is mixed with charged air from an air inlet (109). The mixture of exhaust gas and charged air is passed to a charged air cooler (CAC) (111) after it is compressed through the compressor (110). The charged air cooler (CAC) (111) is placed in proximity to a radiator (112) of the vehicle. Finally, the cooled mixture of exhaust gas and charged air is re-circulated to the intake manifold (102) of the engine (101).

Similarly, in case of conventional high pressure EGR system as shown in FIG. 2, the exhaust gas from the exhaust manifold (103) is bypassed to the EGR cooler (108) through the EGR valve (105), and also is carried to the turbine (105) for driving the compressor (110) of the turbocharger. The charged air form the air inlet (109) is compressed by the compressor (110) of the turbocharger and is passed and cooled in the CAC (111). The cooled charged air and the cooled exhaust gas are mixed at point of dilution, so that the mixture of exhaust gas and charged air is passed to the engine (101) through the intake manifold (103).

As illustrated in FIGS. 1 & 2, the exhaust gas are cooled by passing through the heat exchanger or EGR cooler 108 and the flow control valve (107) for maintaining the desired exhaust gas temperature and the quantity of exhaust gas to be re-circulated in the air intake. The CAC, which acts as a heat exchanger, is used to cool the boosted air charge from the turbocharger compressor outlet prior to entry into the intake manifold of the engine. The engine coolant in the heat exchanger cools the hot exhaust gas before it is passed to the engine. A separate EGR cooler is used to cool the exhaust gases using engine coolant before mixing it with charged air from the compressor (110) of the turbocharger through the CAC (111). This mixture of re-circulated exhaust gas and charged air is introduced into the intake manifold (102) of the engine 1 to enroute the mixture to an engine cylinder for combustion as required to reduce nitrogen oxides emissions from engine exhaust. In both of the conventional EGR systems, the exhaust gas is cooled by the heat exchanger and the separate, dedicated cooler for re-circulation in a controlled manner by an electronically or pneumatically controlled valve for its quantum and temperature by cooling using engine water, into the air intake of the engine to mix with the intake air.

With respect to conventional EGR systems, it is necessary to provide a separate, dedicated cooler for cooling the hot exhaust gas, which increases the number of parts and requires more space. The conventional EGR systems also suffer failures or faults in the EGR valve due to thermal loading by the hot exhaust gas from the engine or the formation of deposits from the exhaust gas, which increases warranty cost. Further, the point of dilution for mixing of re-circulated exhaust gas and cooled charged air is achieved within the engine conduit, which results in improper mixture enters into the engine. Such improper mixture causes degradation in the operation and performance of engine and overall system. Therefore, it is desirable to provide an improved system is developed for system for cooling and re-circulation of dilute mixture of exhaust gas and charged air to an IC engine, which is capable to address and overcome the above disadvantages of conventional EGR systems.

In a conventional system the exhaust gas is cooled and re-circulated in a controlled manner by an electronically or pneumatically controlled valve for its quantum and temperature by cooling using engine water, into the air intake of the engine to mix with the intake air. EGR systems are classified by the method of introduction of the exhaust gas by an external arrangement or by an internal inbuilt arrangement on the engine. The external EGR systems are further classified by the location of mixing point and they are known as high pressure EGR cooling system and low-pressure EGR cooling systems. When the exhaust gases are introduced before turbocharger they are known as low-pressure EGR systems and when introduced after the turbocharger, they are known as high-pressure EGR systems. In case of naturally aspirated engines the low-pressure EGR systems are only applicable.

As illustrated in the figures the exhaust gases are cooled by passing through a heat exchanger and a flow control valve for maintaining the desired exhaust gas temperature and the quantity of exhaust gas to be re-circulated in the air intake. The engine coolant in the heat exchanger cools the hot gases.

Electronic fuel injection systems ask for higher quality of maintenance and good fuel quality as (a) the clearances within the fuel injection system are tight and (b) the pump is lubricated by the diesel fuel. Accidental admission of fuel of indifferent quality (in terms of water content, dust and lubricity) leads to high maintenance cost Therefore, if BS III CEV emission norms are to be implemented widely and painlessly in developing countries, alternative cost-effective solutions must be found. The mechanical fuel injection system lubricated by engine oil is well established and proven in the Indian conditions, because of the robust construction, less maintenance, user friendliness and reliability in the field., The present work successfully explores an engine design rated at 56 kW&102kW with the mechanical fuel injection system to meet the cleaner emission demands for working off-road in severe conditions

Also, the existing EGR systems have the disadvantages of controlling the values either electronically or pneumatically which requires very sophisticated mechanism to operate it. Also, it requires a high pressure fuel injection system to eliminate soot particles from the exhaust gas. The fuel efficiency is very poor in such systems and the performance of the engine gets affected due to such systems. Therefore there is a need of invention which overcomes such disadvantages and drawbacks.

OBJECT OF INVENTION

An object of the present invention is to partially re circulate the exhaust gas from the engine back to the engine by filtering and guiding said exhaust gas through a high pressure line and by allowing said exhaust to get mixed with charged air which is coming from CAC in a low pressure environment and to inject fuel from a low pressure injection system into the combustion chamber of the engine in such a way that combustion of fuel along with the re circulated gas takes place in combustion chamber to reduce Nitric Oxides.

SUMMARY OF INVENTION

According to one aspect of the present invention a system for cooling and circulating exhaust gas in an internal combustion engine is provided which comprises a turbocharger having a turbine and a compressor coupled together, the turbine is operated trough exhaust gas from the engine to drive the compressor, which pumps air by compressing fresh air received from an air inlet unit to a charge air cooler. It comprises at least one exhaust gas filter means attached to an exhaust manifold of the engine for filtering the exhaust gas from the exhaust manifold. It comprises an exhaust gas cooler attached to the exhaust gas filter means for cooling gas from the exhaust gas filter means. It comprises at least one orifice connected to the exhaust gas cooler which in turn is connected to at least one venturi, wherein said venturi is associated to said charge air cooler such that the air from the charge air cooler and gas coming from the orifice is combined in said venturi to form a mixture and the mixture from the venturi is fed to an intake manifold of the engine for combustion and a fuel injection system capable of injecting fuel to the engine.

BRIEF DESCRIPTION OF DRAWINGS

Referring now to the drawings wherein the illustrations are for the purpose of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting the same.

FIG. 1 shows a schematic diagram of a conventional low pressure exhaust gas recirculation (EGR) system for a turbocharged IC engine, in accordance with a prior art;

FIG. 2 illustrates a schematic diagram of a conventional high pressure EGR system for the turbocharged IC engine, in accordance with a prior art; and

FIG. 3 illustrates a schematic diagram of a system for cooling and circulating exhaust gas in an internal combustion engine with low pressure injection system, in accordance with an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 3, a schematic diagram of a system for cooling and circulating exhaust gas in an internal combustion engine is illustrated in accordance with an exemplary embodiment of the present invention. The present invention relates to a system for cooling and circulating exhaust gas in an internal combustion engine (1) which comprises a turbocharger having a turbine (6) and a compressor (7) coupled together, the turbine (6) is operated trough exhaust gas from the engine (1) to drive the compressor (7), which pumps air by compressing fresh air received from an air inlet unit (8) to a charge air cooler (11). It comprises at least one exhaust gas filter means (4) attached to an exhaust manifold (3) of the engine (1) for filtering the exhaust gas from the exhaust manifold (3). It comprises an exhaust gas cooler (5) attached to the exhaust gas filter means (4) for cooling gas from the exhaust gas filter means (4). It comprises at least one orifice (9) connected to the exhaust gas cooler (5) which in turn is connected to at least one venturi (10), wherein said venturi (10) is associated to said charge air cooler (11) such that the air from the charge air cooler (11) and gas coming from the orifice (9) is combined in said venturi (10) to form a mixture (16) and the mixture from the venturi (10) is fed to an intake manifold (2) of the engine through a conduit (18) for combustion and a low pressure fuel injection system (13) capable of injecting fuel to the engine at a low pressure.

In the system, the exhaust gas filter means (4) is capable of filtering soot particles from the exhaust gas.

In the system, the exhaust gas filter means (4) is connected ahead of said turbine such that the exhaust gas filter means (4) partially receives gas from the exhaust manifold.

In the system, the exhaust gas cooler (5) is placed in proximity to a radiator (12) and an engine fan (17) for cooling the filtered exhaust gas from the exhaust gas filter means (4).

In the system, the venturi (10) reduces pressure and delivers the mixture (16) in low pressure to the intake manifold (2) of the engine.

In the system, the fuel injection system (13) is capable of injecting fuel at low pressure to the engine to fire the fuel inside the engine.

In the system, the flow rate of the mixture (16) to the intake manifold (2) is controlled by the orifice (9) and the venturi (10).

In the system, the orifice (9) and the venturi (10) are operated mechanically to obtain a desired flow rate of the mixture (16) coming from the venturi (10).

In the system, conduit (19) present between the exhaust gas filter means and the orifice is at a high pressure and conduit present between the venturi (10) and the intake manifold (2) of the engine is at a low pressure. The system reduces the nitrogen oxide emissions.

In the system, fuel is being fed to the engine at a low pressure by the fuel injection system (13) to control the fuel consumption of the engine.

In the system, the fuel injection system is an inline pump.

In the system, the low pressure at which the fuel is injected by the low pressure fuel injection system is in the range of 650-680 bar (injector side). The high pressure between the exhaust gas filter means and the orifice is in the range of 1.3-1.7 bar (Ex. manifold side). The low pressure between the venturi and the intake manifold of the engine is in the range of 0.7-1 bar (Intake .manifold side). The flow rate (volume) of the mixture to the intake manifold is in the range of 80-90 kg/hr.

In the system, high pressure filtered EGR (Exhaust Gas Re-circulation) system with low pressure fuel injection is used on internal combustion (IC) engines. An EGR cooler is a heat exchanger using engine coolant to cool the exhaust gases from engine before mixing it with charged air coming, through charged air cooler (CAC), from compressor of turbocharger. This mixture of Re-circulated Exhaust gas and charged air is introduced into the intake manifold enroute to engine cylinder for combustion as required to reduce Nitrogen oxides emissions from engine exhaust. A High Pressure filtered EGR system with a low pressure fuel injection system with a dedicated EGR cooler using engine coolant with an orifice for metering the exhaust gas and a venturi for homogenous mixing is the invention applied to turbo charged intercooler IC engines with EGR.

The invention relates to a high pressure EGR system with the features such as high pressure EGR system with low pressure fuel injection equipment. A dedicated filter is used for EGR in a low pressure fuel injection system. An orifice is used to govern amount of exhaust gas re-circulation. No EGR valve is used as in conventional EGR systems. In a conventional engine, the highest warranty cost is due to the failure of the EGR valve. By using an orifice this problem is being overcome. A venturi is used at the point of dilution for better mixing of re¬circulated exhaust gas and cooled charged air and also ensures admission of EGR in the inlet irrespective of the load and speed conditions of the engine. Dedicated EGR cooler using engine coolant may or may not be used.

The present invention includes an internal combustion engine having an intake and exhaust manifold. An intake air conduit extends from compressor of turbocharger to intake manifold. An exhaust conduit extends from exhaust manifold to turbine of turbocharger. It also includes an exhaust gas recirculation conduit from upstream stream of turbocharger (before turbine) to downstream of CAC (after compressor). A dedicated filter is used remove soot from re-circulated exhaust gas. Filtered re-circulated exhaust gas is metered using an orifice plate place in the EGR conduit. Metered quantity of filtered re-circulated exhaust gas is introduced in a venturi placed at the point of dilution of re-circulated exhaust gas and cooled charged air from CAC. This mixture is then introduced in engine cylinder for combustion. CAC can be used to cool both re-circulated exhaust gases and charged air from the compressor of turbo charger, in case of absence of dedicated EGR cooler using engine coolant.

By concept, the new EGR system is implemented without employing a dedicated EGR valve and with a dedicated EGR filter and using low pressure fuel injection equipment. Dedicated EGR cooler using engine coolant may or may not be used.

The present invention relates to usage of High Pressure EGR system with a low pressure fuel injection system with or without a dedicated EGR cooler using engine coolant with an orifice for metering the EGR gases, with a dedicated EGR filter and a venturi for homogenous mixing to achieve emissions performance on any Turbo Charged After-cooled IC engines. This is applicable for both the engines fitted with water to air and air-to-air CACs. The inventors have done their research experiments on two of their IC engines in production employing the new system and achieved the emission performance conforming to BS III CEV emission norms. And have confirmed the feasibility of achieving the same without employing a dedicated EGR cooler cooled by engine coolant.

The present inventions has resulted providing better performance and match the legal requirements.

Fresh atmospheric air from atmosphere through air inlet unit (8) is compressed by the compressor of turbocharger to produce charge air (14). Exhaust gases from exhaust manifold (3) of engine (1) are used to run the turbine 6 of turbocharger. A part of the exhaust gases (amount is governed by using an orifice) from exhaust manifold (3) pass through dedicated EGR filter (4) to trap the soot particles in the high pressure EGR line before it enters into the EGR cooler (5) which uses engine coolant for cooling. At the point of dilution, system employs EGR Venturi (10) to reduce pressure locally and allow mixing of filtered, cooled and metered re-circulated exhaust gases with charge air (14) flown through CAC (11) from compressor (7) and gas mixtures are fed to inlet manifold (2). Low pressure fuel injection system (13) is used for injecting the fuel to the combustion chamber through fuel line for combusting the gas mixture.

The present invention provides a solution for robust and cost effective off-road engine that is economical for backhoe application is developed to meet the Indian BS III CEV (construction equipment vehicle) norms equivalent to the US Tier-3 emission regulation for markets where (a) advanced maintenance facilities are not available in remote areas of operation, (b) availability of the right fuel is not fully assured, (c) the initial cost of the engine is under tight control and (d) the legendary fuel economy of direct injection diesel engines is not traded off when migrating to higher emission norms. The highlights of the layout of the 4-cylinder 3.8-litre 56 kW diesel engine are the use of a high pressure EGR and a proven inline mechanical fuel injection equipment that is easy to maintain and tolerant to indifferent fuel quality. Use of EGR reduces the NOx formation inside the combustion chamber by 30%. The EGR flow is controlled by a calibrated orifice instead of the usual electronically controlled module. With the induction of the EGR gases, fuel injection timing is relatively advanced and the specific fuel consumption of the engine is superior to the competing engines that satisfy similar emission norms. The soot in the EGR is abrasive. To protect the engine parts like the piston, the rings, the liner and the bearings from the abrasive wear, the EGR gases are passed through a wall flow filter for removing 99 % of the soot.

The combustion is characterized by the conventional low-pressure injection pump, and a high pressure filtered EGR system. Further, the system is without electronic interfaces to control the EGR without sacrificing the fuel economy of direct injection diesel engines. As against the conventional cooled EGR system that requires additional sensors, actuators, valves and electronic control logic for monitoring and controlling the EGR rate, a simpler system using a venturi in conjunction with a calibrated orifice is employed.

The engine model with the mechanical fuel injection system and the EGR sub-system consisting of the cooler, the filter, the venturi and the orifice are as shown in Fig. 3. The exhaust gas is taken upstream of the turbocharger turbine to the downstream of the intercooler. The EGR orifice plate is placed before the entrance to the venturi.

The EGR gases contain soot, acid and water vapor which are abrasive and corrosive. These are usually handled by special oils with high dispersancy and higher basicity number (TBN). The reduction in life of the wear components like the valve seats, the piston rings, liner and bearings due to soot is mitigated by a wall-flow filter placed before the cooler in the EGR system. The exhaust soot reacts continuously and passively on the aluminum titanate substrate with the nitrogen dioxide formed at the diesel oxidation catalyst (DOC) ahead of the filter when the gas temperature is beyond 260° C. Since the exhaust temperature of a diesel engine is in the range of 250° C to 500° C active oxidation of carbon by oxygen is possible only when the engine runs at full load. On the other hand, the combustion reactions with N02 at the filter surface takes place at the normal exhaust temperatures of a diesel engine.

The venturi assures a positive pressure difference to drive the EGR gases in the inlet, by decreasing the pressure on the intake side. The pressure drop in the venturi is thermodynamically reversible unlike the-drop across a throttle plate in the inlet duct used in many diesel engines incurring irreversible losses.

The venturi is located on the intake passage downstream of the intercooler. The EGR gas is circumferentially drawn into the intake air stream to mix with the air. The contraction ratio of the venturi defined as the ratio between sectional area of the intake pipe and the sectional area of the nozzle is 0.25.

The modern high pressure electronic fuel injection systems demand high quality fuels in terms of filtering and lubricity. In case an inappropriate fuel is used in remote areas of developing countries, the repair cost and down-time are prohibitive. Therefore, the off road engine was optimized with a mechanical fuel injection system lubricated by the engine oil and an EGR system controlled by a calibrated orifice. The fuel injection equipment is conventional, easy to service and cost-effective as against the electronic high pressure fuel injection equipments used in the other USTier-3 engines, which are sensitive to fuel quality and expensive to maintain. High pressure filtered EGR flow is maintained by a venturi in the inlet to the engine. This engine developed a high back-up torque of 30 % for the backhoe vehicle. The EGR through a regenerative filter is advantageous in reducing the soot by 99 % and hence the wear related problems in a typical EGR engine are avoided. The fuel consumption is on par with the base BSII CEV engine without EGR. The engine is more frugal than the contemporary off-road engines in cost and fuel consumption. Thus, the engine is cost effective, yet advanced and performs convincingly better than the others in this class.

We claim:

1. A system for cooling and circulating exhaust gas in an internal combustion engine, the system comprising:

a turbocharger having a turbine and a compressor coupled together, the turbine is operated trough exhaust gas from the engine to drive the compressor, which pumps air by compressing fresh air received from an air inlet unit to a charge air cooler;

at least one exhaust gas filter means attached to an exhaust manifold of the engine for filtering the exhaust gas from the exhaust manifold;

an exhaust gas cooler attached to the exhaust gas filter means for cooling gas from the exhaust gas filter means;

at least one orifice connected to the exhaust gas cooler which in turn is connected to at least one venturi, wherein said venturi is associated to said charge air cooler such that the air from the charge air cooler and gas coming from the orifice is combined in said venturi to form a mixture and the mixture from the venturi is fed to an intake manifold of the engine for combustion; and

a low pressure fuel injection system capable of injecting fuel to the engine at a low pressure.

2. The system as claimed in claim 1 wherein the exhaust gas filter means is capable of filtering soot particles from the exhaust gas.

3. The system as claimed in claim 1 wherein the exhaust gas filter means is connected ahead of said turbine such that the exhaust gas filter means partially receives gas from the exhaust manifold.

4. The system as claimed in claim 1 wherein the exhaust gas cooler is placed in proximity to a radiator and an engine fan for cooling the filtered exhaust gas from the exhaust gas filter means.

5. The system as claimed in claim 1 wherein the venturi reduces pressure and delivers the mixture in low pressure to the intake manifold of the engine.

6. The system as claimed in claim 1 wherein the fuel injection system is capable of injecting fuel at low pressure to the engine to fire the fuel inside the engine.

7. The system as claimed in claim 1 wherein the flow rate of the mixture to the intake manifold is controlled by the orifice and the venturi.

8. The system as claimed in claim 1 wherein the orifice and the venturi are operated mechanically to obtain a desired flow rate of the mixture coming from the venturi.

9. The system as claimed in claim 1 wherein conduit present between the exhaust gas filter means and the orifice is at a high pressure and conduit present between the venturi and the intake manifold of the engine is at a low pressure.

10. The system as claimed in any one of the preceding claims wherein the system reduces the nitrogen oxide emissions.

11. The system as claimed in any one of the preceding claims wherein fuel is being fed to the engine at a low pressure by the fuel injection system to control the fuel consumption of the engine.

12. The system as claimed in claim 1 wherein the fuel injection system is an inline pump.