Patent Publication Number: US-7591255-B2

Title: Internal combustion engine and EGR heat exchanger for it

Description:
BACKGROUND AND SUMMARY 
   The present invention relates to an internal combustion engine and an EGR heat exchanger for it. 
   There exist internal combustion engines comprising:
         an intake manifold to receive and collect gas to be burnt in an engine cylinder and an exhaust manifold to collect and output exhaust gas from the engine cylinder,   a first turbocharger to compress air to allow more air to fill the engine cylinder, the turbocharger including a first turbine that transforms the exhaust gas flow into mechanical energy to actuate an air-compressor, the turbine having a turbine inlet fluidly connected to the exhaust manifold to receive exhaust gas that operates the turbine and a turbine outlet to output the exhaust gas used to operate the first turbine, and   an EGR (Exhaust Gas Recirculation) device to recirculate exhaust gas, the EGR device comprising an EGR heat exchanger having:   an exchanger inlet fluidly connected to the exhaust manifold through an EGR valve to receive warm EGR gas,   an exchanger outlet fluidly connected to the intake manifold to output cooled EGR gas,   a cooling medium inlet to receive a coolant, and   a cooling medium outlet to output the coolant once it has been used to cool the EGR gas.       

   The existing internal combustion engines may also have a second turbocharger fluidly connected with the first turbocharger to further compress air. Turbochargers are pressure charging devices that further improves engine efficiency by using energy in an exhaust gas to provide pressure charging. Pressure charging an internal combustion engine both increases power and increases efficiency. Pressure charging is a process in which ambient air is compressed to allow more air to fill an engine cylinder. High pressure, high temperature exhaust gas enter a turbine connected to a compressor. As the high pressure, high temperature exhaust gas expands through the turbine, the turbine operates the compressor. As shown in U.S. Pat. No. 3,250,068 issued to Vulliamy on May 10, 1966 shows using turbochargers arranged in a serial fashion. This arrangement allows the turbochargers to be more responsive over a larger operative range and to further increase air pressure in the inlet manifold. 
   To reduce emissions, the exhaust gas recirculation (EGR) device is used for controlling the generation of undesirable pollutant gases in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines. EGR systems primarily recirculate exhaust gas from combustion into the intake air supply of the internal combustion engine. Exhaust gas introduced to the engine cylinder displaces a volume available for fresh air. Reduced oxygen concentrations lower maximum combustion temperatures within the cylinder and slow chemical reactions of the combustion process, decreasing the formation of nitrogen oxides (NOx), for example. Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder. Burning the unburned hydrocarbons further reduces the emission of undesirable pollutants from the internal combustion engine. 
   Cooling recirculated exhaust gas further enhances emissions reductions available through recirculating exhaust gas. Cooling the exhaust gas prior to introduction into the engine cylinder further reduces the combustion temperatures in the engine cylinder. As with lower oxygen concentrations, the reduced temperature of recirculated exhaust gas ultimately lowers production of NOx in the engine cylinder, for example. 
   For instance, such an engine is known from U.S. Pat. No. 6,360,732 in the name of Bailey et al. 
   Many of the internal combustion engine vehicles have also exhaust gas after-treatment device to clean exhaust gas before releasing it into the atmosphere. Well-known after-treatment devices are continuously re-generated diesel particulate filter or SCR (Selective Catalyse Reduction) mufflers. These after-treatment devices work correctly if the temperature of the exhaust gas to be treated is above a given threshold (300° C. for instance). For example, after starting the engine or when the vehicle speed is very low, the temperature of the exhaust gas that flows through the after-treatment device is much lower than 300° C. In those conditions, the exhaust gas cleaning is not as good as when the exhaust gas temperature is above 300° C. 
   It is desirable to provide an internal combustion engine that releases exhaust gas with a higher temperature than usual to improve exhaust gas cleaning, for example. 
   The invention provides, according to an aspect thereof, an internal combustion engine wherein the cooling medium inlet is fluidly connected to the turbine outlet so as to use the exhaust gas outputted by the turbine as the coolant. 
   In the above engine, the exhaust gas that flows to the after-treatment device is warmer than if exhaust gas was not used as a coolant in the heat exchanger. 
   Therefore, this helps the exhaust gas after treatment device to work by increasing the exhaust gas temperature. This also decreases the temperature of EGR gas so that the performance of the engine is increased. 
   The embodiments of the above engine may comprise one or several of the following features:
         the EGR device comprises an EGR cooler which is fluidly connected to the exchanger outlet to cool the EGR gas outputted from the exchanger outlet before readmitting it into the intake manifold, the EGR cooler using a coolant which is different from exhaust gas;   the EGR cooler is also fluidly connected to an outlet of the first turbocharger to receive compressed fresh air and wherein the EGR cooler has a common internal chamber to mix together EGR gas and compressed fresh air as well as to cool EGR gas and compressed fresh air;   the engine comprises a second turbocharger to compress the air that is to be further compressed by the first turbocharger, the second turbocharger including a second turbine that transforms the exhaust gas flow into mechanical energy to actuate a second air-compressor, this second turbine having a turbine inlet to receive exhaust gas that operates the turbine and a turbine outlet to output the exhaust gas used to operate the second turbine, wherein the cooling medium outlet of the EGR heat exchanger is fluidly connected to the turbine inlet of the second turbine or wherein the cooling medium inlet of the EGR heat exchanger is fluidly connected to the turbine outlet of the second turbine to receive the exhaust gas successively expanded by the first and second turbine. The above embodiments of the engine present the following advantages:   using an EGR cooler further decreases the EGR gas temperature so that the engine performance increases and the EGR heat exchanger acts as a pre-cooler and relieves the technical constraints that are used to dimension and build the EGR cooler;   using the EGR heat exchanger to heat the exhaust gas that operates the second turbine of the second turbocharger increases the quantity of mechanical energy that the second turbine retrieves from the exhaust gas flow;   using the exhaust gas released at the outlet of the second turbine improves the efficiency of the EGR heat exchanger because exhaust gas at this outlet is colder than at the outlet of the first turbine. The invention also relates to an EGR heat exchanger suitable to be used in the above internal combustion engine.       

   The invention also relates to a method to operate the above internal combustion engine wherein it comprises the step of admitting exhaust gas outputted by the turbine outlet of the first turbine through the cooling medium inlet so as to use the exhaust gas outputted by the first turbine as a coolant. 
   These and other aspects of the invention will be apparent from the following description, and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of a vehicle having an internal combustion engine equipped with an EGR device; 
       FIG. 2  is a flowchart of a method to operate the engine of the vehicle of  FIG. 1 ; and 
       FIG. 3  is another embodiment of the internal combustion engine of the vehicle of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a vehicle  2  with an internal combustion engine  4 . For example, vehicle  2  is a truck. In the following description, well-known functions or constructions by a person of ordinary skill in the art are not described in details. 
   For example, engine  4  is a two-stage turbo-charging engine having an EGR device. The two-stage turbo-charging engine includes:
         an engine block  6  having cylinders in which diesel and air are admitted to be burnt in order to translate pistons so as to finally rotate vehicle wheels like wheel  10 ,   an intake manifold  12  to receive and collect a mixture of fresh air and EGR gas to be burnt in the cylinders of block  6 ,   an exhaust manifold  14  to collect exhaust gas exhausted from the cylinders of block  6 ,   a first turbocharger  16  that compresses fresh air coming from the vehicle surrounding atmosphere,   a heat exchanger  18  that cools the fresh air compressed by turbocharger  16 ,   a second turbocharger  20  to further compress the fresh air cooled by heat exchanger  18 , and   a charged air cooler  22  to further cool the fresh air compressed by turbocharger  20  before admitting it into manifold  12 .       

   In  FIG. 1 , dotted lines within block  6  represent cylinders. 
   Turbocharger  16  has a turbine  26  that actuates an air compressor  28  through a shaft  30 . 
   Turbine  26  has a turbine inlet  32  to receive the exhaust gas that operates the turbine, and a turbine outlet  34  to output the exhaust gas used to operate the turbine. 
   Compressor  28  has a fresh air inlet  36  to receive captured ambient air at the atmospheric pressure, and an outlet  38  to output pressurized fresh air. 
   Outlet  38  is fluidly connected to an inlet  40  of heat exchanger  18  through a pipe  41  so that the pressurized fresh air flows from outlet  38  to heat exchanger  18 . Heat exchanger  18  has an outlet  42  directly fluidly connected to an inlet  44  of an air compressor  45  of turbocharger  20  through a pipe  46 . 
   Turbocharger  20  has also a turbine  48  to actuate compressor  45  through a shaft  50 . Turbine  48  has an inlet  54  to receive exhaust gas used to operate this turbine and an outlet  56  to output the exhaust gas used to operate turbine  48 . Inlet  54  is directly fluidly connected to an outlet  58  of manifold  14  through a pipe  60 . 
   Compressor  45  further compresses the cooled fresh air outputted by heat exchanger  18  and outputted it through an outlet  61 . 
   Outlet  61  is directly fluidly connected to an inlet  62  of cooler  22  so that the highly pressurized fresh air is admitted into cooler  22 . 
   Cooler  22  has an outlet  64  directly fluidly connected to manifold  12  through a pipe  66  to output cooled charged air into manifold  12 . Cooler  22  has an internal chamber  70  to collect the charged air to be outputted through outlet  64 . For example, cooler  22  has also one or many tubes  72  within which flows a cooling medium like air. Tubes  72  are placed within chamber  70  in thermal contact with the charge air to be cooled. 
   The EGR device includes:
         an EGR valve  80  to capture exhaust gas to be recirculated,   an heat exchanger  82  to cool down the EGR gas, and   cooler  22  to further cool down the EGR gas.       

   Heat exchanger  82  has an inlet  84  to receive EGR gas to be cooled and an outlet  86  to output the cooled EGR gas. Inlet  84  is directly fluidly connected to manifold  14  through a pipe  88 . Valve  80  is placed within pipe  88 . For example, valve  80  is placed at the entrance of pipe  88 . 
   Valve  80  is an electronically controllable valve so that the amount of exhaust gas to be recirculated can be accurately determined. 
   Outlet  86  is directly fluidly connected to inlet  62  through a pipe  90 . Heat exchanger  82  has an internal chamber  92  to collect the EGR gas to be cooled and tubes or plates within which a coolant flows. In  FIG. 1 , for example, the coolant flows within tubes  94  placed within chamber  92  so as to be in thermal contact with the EGR gas to be cooled. 
   Heat exchanger  82  has a cooling medium inlet  96  to receive the coolant used to cool the EGR gas and an outlet  98  used to output the coolant once it has been used to cool the EGR gas. In this embodiment) inlet  96  is directly fluidly connected to outlet  56  through a pipe  100  so as to use the exhaust gas as a coolant. 
   Outlet  98  is directly fluidly connected to inlet  32  through a pipe  102 . Vehicle  2  has also an exhaust gas after-treatment device  110  to clean the exhaust gas outputted by engine  4 . 
   Device  110  has an inlet  112  to receive exhaust gas to be cleaned directly fluidly connected to outlet  34 . Device  110  has also an outlet  114  to output the cleaned exhaust gas into the atmosphere. 
   Arrows in the pipe of  FIG. 1  show the flow directions of the different gases. 
   The operation of engine  4  will now be described with reference to  FIG. 2 . 
   Initially, in step  120 , valve  80  is controlled so as to admit exhaust gas within pipe  88 . The admitted exhaust gas becomes the EGR gas. 
   Then, in step  122 , EGR gas is cooled within heat exchanger  82 . 
   Thereafter, in step  124 , the cooled EGR gas is admitted into cooler  22  through pipe  90 . 
   In parallel, in step  128 , exhaust gas flows to turbine  48 . In step  130 , the exhaust gas flow that is admitted through inlet  54  is transformed by turbine  48  into mechanical energy that actuates compressor  45 . Thus, turbine  48  acts as an expansion engine or a release valve and the exhaust gas pressure drops at the outlet  56 . This also means that the exhaust gas temperature is much lower at outlet  56  than the exhaust gas temperature at inlet  54 . For example, the exhaust gas temperature drop through turbine  48  is equal to about 13O&lt;0&gt;C. 
   In step  132 , the exhaust gas flow, cooled by turbine  48 , is admitted into heat exchanger  82  through the cooling medium inlet  96 . Subsequently, in step  134 , the exhaust gas that flows through tubes  94  is used as a coolant to cool the EGR gas. At the same time, the exhaust gas is heated. In step  136 , the exhaust gas, heated in heat exchanger  82 , flows into turbine  26  through inlet  32 . In step  138 , turbine  26  transforms the heated exhaust gas flow into mechanical energy to actuate compressor  28 . Because the exhaust gas flow admitted into turbine  26  is warmer than if heat exchanger  82  was not used, the amount of mechanical energy that can be retrieved from this flow is higher than if heat exchanger  82  was not used. 
   Finally, the exhaust gas flow used to operate turbine  26  is outputted to after-treatment device  110 . 
   In step  140 , device  110  cleans the exhaust gas before releasing it within the atmosphere. The exhaust gas admitted into device  110  is warmer than if heat exchanger  82  was omitted. Thus, device  110  works better and the exhaust gas released in the atmosphere is cleaner after engine starting or for a very low vehicle speed, for example. 
     FIG. 3  shows another embodiment of an internal combustion engine  150  suitable to be used within vehicle  2 . 
   The features of engine  150  which are identical to features of engine  4  have the same numeral references. 
   Engine  150  differs from engine  4  by the two following features:
         heat exchanger  82  is placed at the outlet of turbine  26 , and   cooler  22  is replaced by two independent coolers  154  and  156 .       

   In  FIG. 3 , cooling medium inlet  96  is directly fluidly connected to outlet  34  of turbine  26  and outlet  98  is directly fluidly connected to inlet  112  of device  110 . At the outlet of turbine  26 , the exhaust gas temperature is lower than at outlet  56  because the exhaust gas has further been expanded by turbine  26 . As a result, the efficiency of heat exchanger  82  is increased and the EGR gas outputted through outlet  86  is colder than in the embodiment of  FIG. 1 . 
   In  FIG. 3 , cooler  22  of  FIG. 1  is replaced by EGR gas cooler  154  and an independent air cooler  156 . 
   Coolers  154  and  156  use a different cooling medium from the one used in heat exchanger  82 . For example, the cooling medium is water or fresh air. 
   Cooler  154  has an inlet  158  directly fluidly connected to outlet  86  to receive the EGR gas to be further cooled, and an outlet  160  to output the further cooled EGR gas into manifold  12 . 
   Cooler  156  has an inlet  162  directly fluidly connected to outlet  61  of compressor  45 . Cooler  156  has also an outlet  164  directly fluidly connected to manifold  12 . In this embodiment, cooler  154  is only used to cool EGR gas and cooler  156  is only used to cool compressed fresh air. 
   The operation of engine  150  can be deduced from the operation of engine  4 . 
   Many other embodiments are possible. For example, in the embodiment of  FIG. 1 , cooler  22  can be replaced by independent coolers  154  and  156  like this is described in view of  FIG. 3 . 
   In  FIG. 1 , for a low cost embodiment, turbocharger  16  can be omitted. Thus, outlet  98  is directly fluidly connected to inlet  112 . The internal combustion engine can be used within any kind of vehicle like cars or boats but also outside any vehicle like for example in a diesel-electric generating set. 
   Valve  80  can be placed elsewhere to captured exhaust gas. For example, valve  80  can be placed after outlet  86  or after outlet  160  in  FIG. 3 . 
   In a low cost embodiment, cooler  154  of the embodiment of  FIG. 3  can be omitted. 
   The cooling medium used in heat exchanger  18 , cooler  22 , coolers  154  and  156  can be of any type like, for example, water or fresh air. Tubes  94  can be replaced by plates or other suitable shapes. 
   LIST OF REFERENCES 
   
       
       
         
             2  vehicle 
             4  engine 
             6  engine block 
             10  wheel 
             12  intake manifold 
             14  exhaust manifold 
             16 ,  20  turbochargers 
             18 ,  82  heat exchangers 
             38 ,  42 ,  61 ,  64 ,  164  air outlets 
             36 ,  40 ,  44 ,  62 ,  162  air inlets 
             22 ,  154 ,  156  coolers 
             26 ,  45  turbines 
             32 ,  54 ,  112 ,  158  exhaust gas inlet 
             34 ,  56 ,  114 ,  160  exhaust gas outlet 
             28 ,  45  air compressors 
             30 ,  50  shafts 
             41 ,  46 ,  60 ,  88 ,  90 ,  100 ,  102  pipes 
             70 ,  92  internal chambers 
             72 ,  94  tubes 
             80  EGR valve 
             96  cooling medium inlet cooling medium outlet o after-treatment device 0 internal combustion engine