INTAKE AIR AND EGR GAS MIXING SYSTEM FOR AN IC ENGINE

FIELD OF INVENTION

The present invention relates to the fields of exhaust gas recirculation for internal combustion engines, and more particularly to a system for improving the rate of mixing of the intake air and the EGR gas, through optimizing the inlet manifold with larger injection area, by providing a half bluff body arrangement at the mixing chamber on the inlet manifold.

BACKGROUND OF INVENTION

An internal combustion engine usually requires exhaust gas recirculation (EGR) to the engine to comply with engine exhaust regulations in order to meet the NOx emissions norms. Various methods and devices are known for exhaust gas recirculation, and normally a portion of exhaust gas from the engine cylinders are diverted to mix with the intake charge air. The experimental results of internal combustion engine with EGR for part load condition reveals, there is favorable condition for EGR gas and air mixing above 2000 rpm, due to positive pressure. But below 2000 rpm, the conditions are not favorable for mixing, as the boost air pressure is greater than exhaust gas pressures. This shows that there is no uniform distribution of EGR gas inside the intake manifold of the engine and hence the intake manifold optimization is required.

Homogeneous mixing and equal distribution of EGR gas into the intake charge air and making availability of the EGR gas into each of the cylinder in required level is important for achieving compliance with exhaust gas regulations and maintaining acceptable level of engine operation. Air system permeability must be kept in sufficient level to guaranty the volumetric efficiency and performance of the engine.

The non-homogenous mixture distribution potentially may not only cause emissions outside a required range but may also cause engine misfire, as well as variations in cylinder pressure across pistons of the engine, causing the engine to work improperly. Improper mixing of EGR gas will cause increase in smoke level, hence required modifications to be made in the air flow passage, such that all the cylinders get uniform mixture of EGR gas and air. In order to choose the homogenous mixing proportion of the EGR gas with intake air possible designs are analyzed with appropriate boundary conditions and optimized design is investigated. To achieve proper mixing various design concepts are analyzed for the engine. Accordingly there exists a need for a more homogenous mixing of recirculated exhaust gas and intake air being fed to such an engine.

The Fig. 1 shows a conventional system having EGR injection made by providing a set of holes in the EGR pipe to increase the mixing rate. The EGR pipe (1) is made inserted into the intake manifold (2) and a set of holes (3) are formed in the inserted portion of the EGR pipe (1) to inject the EGR gas into the intake manifold of the engine. However the analysis did not give any successful result in respect of the mixing rate and flow distribution. Sufficient amount of EGR gas is not being injected into the main stream of intake air. In order to overcome this problem, a low pressure region is locally created before the EGR injection.

The Fig. 2 shows another conventional system having a low pressure region created before the EGR injection. This system is achieved by providing an EGR pipe (1) with small injection area into the intake manifold (2) and keeping a bluff body (3) in the air flow path inside the air duct area. The analysis of this arrangement shows that the average volume fraction for the EGR gas is increased, and a greater amount of EGR is injected into the low pressure region, which is created by the bluff body at the air duct, the results are obtained even at below 2000 rpm levels.

The analysis reveals that the smaller pipe injection with bluff body gives good results, however obstruction losses are obtained in the gas flow. The system needs to be improved to obtain better results in terms of mixing rate and flow distribution.

FIG. 3 shows a schematic diagram of a conventional EGR mixing system having larger EGR pipe area without bluff body. This arrangement allows the amount of EGR to increase by increasing the area of injection in the pipe even at 1800 rpm. The EGR pipe (1) is inserted into the intake manifold (2) with bluff body (3) such that the injection area is larger in comparison to the above disclosed conventional arrangements for EGR gas mixing into the intake air. The analysis results of the system EGR mixing in intake manifold with larger injection area showed better amount of EGR mass fraction, however this EGR mixing design arrangement also suffers to meet the requirements across all engine operating speeds.

The FIG. 4 shows a schematic diagram of a conventional EGR mixing system having small EGR injection pipe with injection holes for mixing the EGR gas and the intake air in the air duct. The EGR pipe (1) with small injection holes is inserted into the intake manifold is provided in the air flow path inside the air duct area (2). The results shows that the system needs to be improved to obtain better results in terms of mixing rate and flow distribution, still there needs some improvement to optimize the mixing and obtain benefits.

In view of all the above discussed EGR gas mixing arrangements, the conventional intake manifold design is not providing proper homogeneous EGR mixing, further due to the uneven distribution of air pressure inside the cylinders, the conventional intake manifold with this EGR suffers increased level of smoke and not capable of meeting required emission norms.

The conventional mixing system needs to be optimized to give enhanced mixing rate of gases and equal EGR gas percentage provided to all the cylinders. The volumetric efficiency has to be maintained to achieve the rated engine power. Hence the design of the mixing system needs to be improved by considering the design, reliability and cost. The pipe injection with arrangement gives increased amount of EGR gas, and there is greater need to address some more issues related to uniform distribution of EGR gas to all the cylinders.

Therefore, it is desirable to provide an improved EGR and intake air mixing system for engines having optimized inlet manifold design delivering more homogenous mixture of intake air and EGR gas to all cylinders with better EGR mass fraction even at part load condition and at different speed levels. The flow distribution of the EGR gas and intake air mixture needs to be improved to obtain enhanced performance of the engine and various advantages.

SUMMARY OF INVENTION:

The main objective of the present invention is to provide an EGR and intake air mixing system having optimized manifold design which enables better EGR mass fraction to all cylinders at different speed levels of the engine.

Another objective of the present invention is to provide an EGR and intake air mixing system which enables to cater the pressure loss with improved design, reliability and cost.
Further objective of the present invention is to provide an EGR and intake air mixing system which allows for homogeneous mixing of exhaust recirculation gas with intake air for various EGR operating conditions of the engine, even during the low EGR pressures.

The present invention, which achieves tine objectives, relates to a system for improving the rate of mixing of the intake air and the exhaust gas recirculation EGR gas, through optimizing the engine inlet manifold with larger injection area, by providing a half bluff body arrangement at the mixing chamber on the inlet manifold. The system according to the present invention achieves optimized manifold design and enables better EGR mass fraction to all cylinders at different speed levels of the engine, even during the part load conditions.

The EGR gas and intake air mixing system comprises an intake conduit for supplying intake charge air into the engine for combustion process. The intake conduit serving as inlet manifold includes an air duct having a half bluff body arrangement, such that the half bluff body arrangement provided in the air duct is placed at a distance from the engine intake. An exhaust gas recirculation pipe is provided for injecting a portion of exhaust gas into the intake charge air. The EGR pipe is placed between the engine intake and the half bluff body arrangement, such that the injected exhaust gas mixes with the intake charge air and enters into the engine cylinder for combustion.

The half bluff body arrangement provided in the intake manifold creates a low pressure region at the air duct and enables homogenous mixing of the exhaust gas and intake charge air and for uniform distribution of gases into all engine cylinders. The combined arrangement of the half bluff body arrangement and the pipe for exhaust gas recirculation allows for proper mixing of the exhaust gas and the intake charge air in required proportion. The EGR gas entering inside the air duct through the larger injection area pipe and the intake charge air entering through the half bluff body arrangement creates an increased pressure condition for the EGR gas to flow inside the air duct and to mix with the intake charge air homogeneously, and this homogenous mixing provides a greater level of EGR mass fraction.

The EGR gas and the intake air mixing system according to the present invention increases the intake charge air and EGR gas mixing rate and thereby supplying more homogenous mixing of the intake air and EGR gas to all the cylinders with uniform distribution and improving the engine performance. The mixing concept of present invention is experimentally investigated for the smoke level on the engine test bench at part load conditions and achieved better results. The results have proved that there is significant reduction in the smoke level for larger injection area and half bluff body arrangement. This optimized manifold design provided better EGR mass fraction of approximately 20 % for all the cylinders at 1800 rpm for part load condition. Due to this design even during low EGR pressures, mixing of exhaust gas with air will be better for all the EGR operating conditions.

The present invention provides optimized intake manifold design for exhaust gas recirculation EGR gas and the intake air mixing, which enables greater EGR mass fraction and more homogenous mixture to all cylinders at different speed levels of the engine. This homogeneous mixing of exhaust gas with air provides better operating condition and improved engine performance for all the EGR operating conditions, even during low EGR pressures.

BRIEF DESCRIPTION OF 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.

FIG. 1 shows a schematic diagram of a conventional EGR gas and intake air mixing system having EGR injection pipe with holes for injection of EGR gas into the intake manifold, in accordance to the prior art.

FIG. 2 shows a schematic diagram of a conventional EGR gas intake charge air mixing system having small injection area pipe with bluff body, in accordance to the prior art.

FIG. 3 shows a schematic diagram of a conventional mixing system with larger EGR injection area pipe and bluff body, in accordance to the prior art.

FIG. 4 shows a schematic diagram of a conventional EGR mixing system having small EGR injection pipe with injection holes for mixing the EGR gas and the intake air in the air duct, in accordance to the prior art.

FIG.5 illustrates a schematic arrangement of the mixing system, having EGR pipe with larger injection area and half bluff body arrangement in intake manifold, with an exemplary embodiment of the present invention.

FIG.6 shows air duct with half bluff body arrangement inside the duct through which the intake air flows and mixes with EGR gas, in accordance to the present invention.

FIG.7 illustrates the mixing inside the intake manifold, and the mixed gas flow through a larger injection area and the half bluff body arrangement, in accordance to the present invention.

FIG.8 shows the table instructing the uniformity in average EGR volume for all the cylinders, in accordance to the present invention.

FIG.9 illustrates graphical representation of uniformity in intake pressure distribution between all the runners for 25% and 50% load with the optimized manifold, in accordance to the present invention.

DETAILED DESCRIPTION:

The present invention relates to the system for homogenous mixing of recirculated exhaust gas and intake charge air mixture and better cylinder-to-cyiinder flow distribution of the mixed gases for combustion process, and thereby improving the engine performance and achieving the required emission norms at various engine operating conditions.

Modern Diesel engines are commonly turbocharged, in such case proper mixing of recirculated exhaust EGR gas and intake charge air will take place only when the turbine upstream pressure is sufficiently higher than the boost pressure. In case the pressure difference is not enough to meet the engine requirements alternate solution must be arrived by either increasing the turbine upstream pressure or reducing the boost pressure by providing the obstruction locally in the air flow passage inside the air duct without affecting the engine performance. The engine considered is a multi cylinder engine with the intake valve opening at 240 deg crank angle. Initially when the first cylinder is open i.e. first runner will be opened and other two runner exit will be closed implying that first cylinder is opened and other two cylinders closed. Similarly when the second runner is opened, the first and third runner will be closed. And finally when the third runner is opened, the first and second runner will be closed. The time for gas flow through the runner exit will be dependent upon the speed of the engine.

FIG.5 illustrates a schematic arrangement of the mixing system, having EGR pipe with larger injection area and half bluff body arrangement in intake manifold, with an exemplary embodiment of the present invention. The recirculated exhaust gas and the intake air mixing system comprising an intake conduit 1 for supplying the intake charge air into the engine for the combustion process.

The intake conduit 1 serving as inlet manifold includes an air duct 2 having a half bluff body arrangement 3, such that the half bluff body arrangement 3 provided in the air duct 2 is placed at a distance from the engine intake 4. An exhaust gas recirculation pipe 5 is provided for injecting a portion of exhaust gas into the intake charge air. The EGR pipe 5 is placed between the engine intake 4 and the half bluff body arrangement 3, such that the injected exhaust gas mixes with the intake charge air and enters into the engine cylinder for combustion.

FIG. 6 shows air duct with half bluff body arrangement inside the duct through which the intake air flows and mixes with EGR gas, in accordance to the present invention. The half bluff body arrangement 3 provided in the intake manifold 1 creates a low pressure region at the air duct 2 and enables homogenous mixing of the exhaust gas and intake charge air and for uniform distribution of gases into all engine cylinders. The EGR gas entering inside the air duct 2 through the larger injection area pipe 5 and the intake charge air entering through the half bluff body arrangement 3 creates an increased pressure condition for the EGR gas to flow inside the air duct 2 and to mix with the intake charge air homogeneously, and this homogenous mixing provides a greater level of EGR mass fraction.

The mixing system according to the present invention gives a positive pressure difference, by decreasing the pressure on the intake side. Through the EGR pipe 5 and injection area the recirculated exhaust gas is circumferentially drawn into the intake air stream and mixes with the charge air. With this system, the boost pressure is once reduced in the EGR entry section, but a pressure is re-established to the original boost pressure downstream of that section. This optimized manifold gives almost equal EGR gas percentage for all the three cylinders and at the same time volumetric efficiency is not reduced to greater extent from simulated volumetric efficiency to give required power.

The parametrical studies are carried out to improve the mixing of the EGR gas and the intake air and experimentally investigate by measuring the smoke level for various engine speeds for part load conditions. For the simulation two fluids namely air and exhaust gas (mixture of C02 (10%), N2 (80.1%), 02 (0.3%), CO (6%), H2 (3%) and CH4 (0.4%) by volume) is used. The composition used for exhaust gas is typical exhaust gas composition of a diesel engine

Following boundary conditions are used for the computational fluid dynamics CFD analysis, (a) Air inlet condition: Compressor outlet pressure and temperature are taken from the engine test data, (b) EGR inlet condition: Exhaust manifold pressure, which is measured before the exhaust gas enters the air duct, (c) Outlet condition: The average pressure prevalent in the respective cylinder during the intake stroke.

The meshes generated in ICEM CFD and CFX solver is used for solving the governing equations. A grid independence study is carried out for the initial model and mesh with 0.6 million tetrahedral cells are found to be adequate for capturing the results accurately.

A prism cell is used to capture the boundary layer. All the simulations were carried out below 2000 rpm and particularly at 1800 rpm because the EGR will be frequently operated at part load conditions. Further the pressure difference for EGR to mix with air is not favorable at part load conditions. So at this engine speed, if homogenous mixture is favorable then it will mix properly for other engine speed conditions also.
The flow through an intake manifold is dependent on the time since crank angle positions vary with respect to time. The unsteady state simulation can predict the real working conditions of an engine intake manifold. The boundary conditions are no longer constant but vary with time. These boundary conditions are obtained from CFD software by carrying out different steady state analyses.

FIG.7 illustrates the mixing of recirculated exhaust gas and intake charge air inside the intake manifold, and the mixed gas flow through a larger injection area and the half bluff body arrangement, in accordance to the present invention. The analysis and results reveals that the smoke level is low, and the EGR gas (1) and intake air (2) mixing takes place in a proper mode and due to this the resulting mixture is found to be a homogenous mixture for combustion into the engine. The smoke level for conventional manifold design is found to be higher when compared to the optimized inlet manifold with larger injection area in accordance to the present invention.

FIG.8 shows the table instructing the uniformity in average EGR volume for all the cylinders, in accordance to the present invention. The recirculated exhaust gas flow to all the cylinders is found to be uniform in distribution at various operating conditions and at different speed levels. The mass flow and the volume fraction of the EGR gas is found to be satisfactorily level.

FIG.9 illustrates graphical representation of uniformity in intake pressure distribution between all the runners for 25% and 50% load with the optimized manifold, in accordance to the present invention. From the fig it is evident that the pressure difference between all three runners is found to be uniform for 25 % and 50% load for the optimized manifold with larger injection area. Due to this uniform distribution the smoke level is reduced and engine performance in terms of power is increased.

The mixing of intake charge air and the exhaust gas in accordance to the present invention provides a homogenous mixture of intake charge air and recirculated exhaust gas for all the intake manifold runners of the inline engine by maintaining positive pressure for the exhaust gas to flow inside the air duct during transient conditions.

The present invention provides optimized manifold design for EGR and intake air mixing which enables better EGR mass fraction and more homogenous mixture to all cylinders at different speed levels of the engine. This homogeneous mixing of exhaust gas with air provides better operating condition and improved engine performance for all the EGR operating conditions, even during low EGR pressures. The parameter mixing length, which is the distance between the EGR injection point and the intake manifold, is maintained in optimum level, and this air EGR mixing system employed improves the mixing phenomena and takes care of the pressure losses.

The mixing arrangement of present invention having EGR injection with larger area and half bluff body concept provided better EGR and air mixing with optimized manifold design. The travel time between the EGR injection and the engine combustion chamber is maintained as short as possible in particular during transient phases operating conditions, this allow induction of EGR toward intake side and to make the system more efficient.

The foregoing description is a specific embodiment of the present invention. It should be appreciated that this embodiment is described for purpose of illustration only, and that numerous alterations and modifications may be practiced by those skilled in the art without departing from the spirit and scope of the invention. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.

We claim:

1. An EGR gas and intake air mixing system for an IC engine comprising,

an intake conduit for supplying intake charge air into the engine, with an air duct having a half bluff body arrangement, wherein the half bluff body arrangement is provided at a distance from the engine intake;

a pipe for injecting a portion of exhaust gas into the intake charge air is placed between the engine intake and the half bluff body arrangement, such that the injected exhaust gas mixes with the intake charge air and enters into the engine cylinder for combustion.

wherein the half bluff body provided in the intake manifold creates a low pressure region at the air duct and enables homogenous mixing of the exhaust gas and intake charge air and for uniform distribution of gases into all engine cylinders.

2. The EGR gas and intake air mixing system as claimed in claim 1, wherein the cross section area of said bluff body at the intake duct being at least 30% of the cross sectional area of end portion of the intake duct.

3. The EGR gas and intake air mixing system as claimed in claim 1, wherein the EGR pipe is placed between the engine intake and the half bluff body arrangement, such that the injected exhaust gas mixes with the intake charge air and enters into the engine cylinder for combustion.

4. The EGR gas and intake air mixing system as claimed in claim 1, wherein the engine considered is a multi cylinder engine.

5. The EGR gas and intake air mixing system as claimed in claim 1, wherein the intake valve opening of said engine is provided at 240 deg crank angle.

6. The EGR gas and intake air mixing system as claimed in claim 1, wherein the intake conduit supplies the intake charge air into the engine for the combustion process.

7. The EGR gas and intake air mixing system as claimed in claim 1, wherein the exhaust gas recirculation pipe injects a portion of exhaust gas into the intake charge air.

8. The EGR gas and intake air mixing system as claimed in claim 1, wherein the EGR gas pipe is integrated into the intake duct of the engine.

9. The EGR gas and intake air mixing system as claimed in claim 1, wherein the EGR pipe mixes the exhaust gas in a flow perpendicular to the flow of the intake air through the intake duct.