Patent Publication Number: US-2023146605-A1

Title: A turbocharged engine system and a method of controlling boost pressure

Description:
FIELD OF THE INVENTION 
     The present invention relates to a turbocharged engine system comprising an electric compressor and, in particular, to a system where the electric compressor is arranged to inject a compressed fluid into the exhaust subsystem of turbocharged engine upstream of the turbocharger. Further, the present invention relates to a method of controlling the boost pressure supplied to a turbocharged engine by injecting a stream of compressed fluid into an exhaust stream of the engine upstream of the turbocharge. 
     BACKGROUND OF THE INVENTION 
     Internal combustion engines are often accompanied by a turbocharger within an engine system. The turbocharger increases the efficiency of an engine system by extracting work from hot exhaust gases emitted by the internal combustion engine and using this work to force air into the internal combustion engine; increasing the mass of air available for combustion. This increase in the pressure or mass of the air entering the internal combustion engine is commonly known as boost pressure or boost. The use of a turbocharger can improve the power output and/or improve fuel efficiency of the internal combustion engine and reduce emissions of certain species such as particulate matter and nitrous oxides NO x . 
     Nevertheless, turbocharged internal combustion engines suffer from several drawbacks. For example, present systems are often unable to increase engine load rapidly in response to transient load events, due to a lag between the event and the turbocharger&#39;s ability to increase the boost pressure. This lag is commonly known as turbo lag. 
     A number of technologies or solutions exist to reduce turbo lag. However, each of these technologies possesses significant drawbacks itself. 
     For example, superchargers—which are also known as electric superchargers, E-compressors, electric compressors—inject air mass into a turbocharged internal combustion engine prior to combustion. However, the ability of superchargers to reduce turbo lag is limited by the turbocharger compressor surge line and, therefore, the rate at which the boost pressure and engine load can be increased is limited and turbo lag is still observed. 
     E-turbochargers—also known as electrically assisted turbochargers or e-turbos—aim to solve turbo lag by electrically assisting the acceleration of the turbocharger and thereby improving responsiveness. However, electrically assisted turbochargers are often difficult to design, integrate and control such that their associated costs often significantly outweigh their benefits. Furthermore, it is typically not possible to convert an existing turbocharger into an e-turbocharger, limiting this the application of this technology. 
     Another potential solution is the use of variable geometry turbochargers. In this type of turbocharger, the aspect ratio of turbocharger can be changed to suit the engine load and thereby reduce turbo lag. However, variable geometry turbochargers are costly and complex to design and are often unreliable due to the inherent incompatibility of high temperatures and the intricate moving parts required to adjust the aspect ratio. For these reasons, variable geometry turbochargers are typically not designed or used with larger, more powerful internal combustion engines or efficient high-temperature internal combustion engines. 
     Objects and aspects of the present invention aim to alleviate the problems associated with the turbocharged internal combustion engines and the present technologies used to reduce turbo lag. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a turbocharged engine system comprising: an internal combustion engine, the internal combustion engine in fluid communication with an intake subsystem and an exhaust subsystem; a turbocharger arranged to supply a boost pressure to the internal combustion engine via a turbine coupled to a compressor wheel, the turbine being located in the exhaust subsystem and the compressor wheel being located in the intake subsystem; and an electric compressor arranged to inject a compressed fluid into the exhaust subsystem upstream of the turbine such that, in use, the compressed fluid injected by the electric compressor into the exhaust subsystem maintains the speed of or accelerates the turbine and thereby maintains or increases the boost pressure supplied to the internal combustion engine by the turbocharger. 
     The injection of the compressed fluid, typically compressed air, into the exhaust subsystem by the electric compressor can be used to maintain the speed of or accelerate the turbine as the mass flow through and the expansion ratio across the turbine has been maintained or increased. This in turn maintains the speed of or accelerates the compressor wheel of the turbocharger which maintains or increases the boost pressure supplied to the engine due to the power imbalance between the compressor wheel and the turbine of the turbocharger. Since the electric compressor can be controlled independently to and can respond more quickly than the turbocharger, the electric compressor can effectively assist in controlling the boost pressure supplied and make the turbocharger more responsive. In this way, the turbo lag and transient load acceptance response times can be reduced. 
     The turbocharged engine system in accordance with the present invention is particularly beneficial for systems used in the high and medium power generation markets as it improves cold/pre-heated engine start times opening the potential for natural gas engines in the grid balancing, secondary frequency, emergency standby and datacentre markets. These markets are currently dominated by the less efficient and more polluting diesel engines. Another benefit of the turbocharged engine system is that the base design of the engine, efficiency or peak load of the engine do not need to be sacrificed in order to incorporate the electric compressor. 
     Furthermore, the provision of such an electric compressor is beneficial as once the desired boost pressure has been achieved the amount of compressed fluid supplied by the electric compressor can be reduced to avoid increasing the boost pressure over a desired or optimal value. In this way, the electric compressor can prevent the boost pressure from negatively affecting the internal combustion engine or its performance by, for example, overloading. 
     The provision of an electric compressor is also advantageous over other solutions to reducing turbo lag as it can be retrofitted to existing turbocharged engine systems relatively easily as only the exhaust subsystem needs to be altered to allow the injection of compressed fluid from the electric compressor. 
     The turbocharged engine system may comprise one or more control valves arranged to control the injection of the compressed fluid into the exhaust by the electric compressor. Control over the injection of the compressed fluid by the one or more control valves may comprise controlling the timing, pressures and quantity of the injection. The provision of one or more control valves is advantageous as it affords an additional way to control the amount, or mass flow, or timing, of compressed fluid injected into the exhaust subsystem. 
     The one or more control valves may comprise one or more of an isolation valve, a blow-off valve, a check valve and a bypass valve alone or in any combination. 
     Preferably, the turbocharged engine system comprises two control valves. In one preferred embodiment, the two control valves are an isolation valve and a bypass valve. In a second preferred embodiment, the two control valves are a blow-off valve and a check valve. 
     Preferably, one or more of the control valves are arranged to be mechanically actuated. Preferably, one or more control valves are arranged to be mechanically actuated at set, or pre-determined, pressures. 
     Preferably, one or more of the control valves are arranged to be electronically controlled. 
     Preferably, one or more of the control valves are arranged to be an open-close valve. An open-close valve can only be set to a fully open position or a fully closed position. The provision of open-close valve is beneficial as it simplifies controlling the actuation of the control valves. 
     Alternatively, one or more of the control valves are arranged to have full authority over their position, such that they can be set to any position intermediate to the open position and the close position. The provision of control valves with full authority of their position improves the level of control afforded over the amount, or mass flow, or timing, of compressed fluid injected into the exhaust subsystem. 
     The one or more control valves may comprise an isolator valve arranged to prevent or inhibit the stream of compressed fluid into the exhaust subsystem. Usually, actuation of the isolator valve controls the flow of the compressed fluid into the exhaust subsystem by partially or fully occluding the conduit along which the stream of compressed fluid is flowing. Typically, the isolator valve is located between the electric compressor and exhaust subsystem. Additionally, the isolator valve can be actuated to prevent the back flow, which when exhaust fluid in the exhaust subsystem flows towards the electric compressor, 
     The one or more control valves may comprise a bypass valve arranged to bypass the electric compressor. The bypass valve can be actuated to lower the pressure of the compressed fluid as well as increasing the mass flow through the electric compressor by mixing it with non-compressed fluid, typically air. This is particularly advantageous when the operating point of the electric compressor approaches the surge line i.e. when the compressor ratio increases or the mass flow through the compressor decreases. Thus, the bypass valve can prevent compressor surge events on the electric compressor. 
     The one or more control valves may comprise a blow-off valve arranged to control the venting of the compressed fluid produced by the electric compressor into the external environment. Compressed fluid can be vented to limit the pressure of the pressure-boosted stream and therefore the boost pressure supplied to the internal combustion engine. This is particularly advantageous when the operating point of the electric compressor approaches the surge line. Thus, the blow-off valve can prevent compressor surge events on the electric compressor. Additionally, compressed fluid can be vented to allow the electric compressor to accelerate to a desired speed at a lower pressure putting less load on the electric motor and speeding up the acceleration of the electric motor. 
     The one or more control valves may comprise a check valve arranged to prevent fluid in the exhaust subsystem flowing towards the electric compressor. The check valve—also known as a clack valve, non-return valve, reflux valve, retention valve or one-way valve—prevents the flow of exhaust fluid from exhaust subsystem towards the electric compressor. Additionally, the provision of a check valve controls the injection of compressed fluid as fluid will only be injected into the exhaust subsystem when the pressure of the compressed fluid is greater than the pressure of the fluid within the exhaust subsystem. 
     According to a second aspect of the present invention there is provided a method of controlling the boost pressure supplied to an internal combustion engine by a turbocharger, said method comprising the steps of:
         producing a stream of compressed fluid;   injecting the stream of compressed fluid into an exhaust stream of the internal combustion engine to produce a pressure-boosted exhaust stream; and   controlling the speed of a turbine of the turbocharger using the pressure-boosted exhaust stream such that the boost pressure supplied to the internal combustion engine is controlled.       

     The production of a stream of compressed fluid and the injection of the stream of compressed fluid afford control over the speed of the turbine. In this way, method provides control over the amount, or mass flow, or timing, of the stream of compressed fluid injected into the exhaust stream. Thus, turbo lag of the turbocharged internal combustion engine can be reduced as the turbocharger can be independently controlled by injection of the compressed fluid into the exhaust stream. This advantageously improves the response of the turbocharged engine to transient load events. 
     Preferably, the method controls the boost pressure supplied to the internal combustion engine by maintaining or increasing the boost pressure supplied to the internal combustion engine, such that the step of controlling the speed of the turbine comprises the step of maintaining the speed of or accelerating the turbine of the turbocharger using the pressure-boosted exhaust stream, thereby maintaining or increasing the boost pressure supplied to the internal combustion engine. 
     Increasing the boost pressure by accelerating the turbine using the injected stream of compressed fluid can be advantageously used to reduce turbo lag. Maintaining the boost pressure by maintaining the speed of the turbine using the injected stream of compressed fluid can be advantageously used to respond to fault conditions. For example, if the internal combustion engines experiences a fault condition such as coming off load, the boost pressure can be maintained such that the internal combustion engine can spin up more quickly, which saves time during its acceleration and reduces the impact of the fault condition. 
     The method may comprise the additional step of reducing the amount, or mass flow, of compressed fluid injected into the exhaust stream when the load of the internal combustion engine or boost pressure approaches, achieves or exceeds a threshold or predetermined value. The boost pressure may represent the surge line of turbocharger. 
     Preferably, the method comprises the additional step of reducing the amount, or mass flow, of compressed fluid injected into the exhaust stream when the load of the internal combustion engine, or engine load, or boost pressure achieves or exceeds a threshold or predetermined value. 
     Preferably, the step of reducing the amount of compressed fluid injected into the exhaust stream comprises a step of reducing the pressure of the compressed fluid stream. 
     Preferably, the step of reducing the amount of compressed fluid injected into the exhaust stream comprises a step of restricting the flow of compressed fluid into the exhaust stream. 
     Preferably, the method comprises an additional step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream when the load of the internal combustion engine, or engine load, or boost pressure approaches, is below or falls below a threshold or predetermined value. 
     Preferably, the method comprises an additional step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream when the load of the internal combustion engine or boost pressure is below or falls below a threshold or predetermined value. 
     Preferably, the step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream comprises a step of increasing the pressure of the compressed fluid stream. 
     Preferably, the step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream comprises a step of increasing the flow of compressed fluid into the exhaust stream. 
     Preferably, the step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream comprises a step of increasing the proportion of the compressed fluid stream that is injected into the exhaust stream. 
     Preferably, the step of reducing the amount, or mass flow, of compressed fluid injected into the exhaust stream or the step of increasing the amount of the compressed fluid injected into the exhaust stream comprises a step of venting at least some of the compressed fluid into the external environment or bypassing the electric compressor. 
     Preferably, the step of reducing the amount, or mass flow, of compressed fluid injected into the exhaust stream comprises a step of venting at least some of the compressed fluid into the external environment. 
     Preferably, the step of increasing the amount, or mass flow, of the compressed fluid injected into the exhaust stream comprises a step of bypassing the electric compressor. Preferably, the step of bypassing the electric compressor comprises feeding the stream of compressed fluid back into the electric compressor. In this way, the electric compressor can be ramped or span up to a desired speed and produce a desired pressure prior to the injection of stream of compressed fluid into the exhaust stream. 
     Preferably, the stream of compressed fluid is compressed air. One advantage of using compressed air is the readily availability of air such that a dedicated fluid supply or tank is not required. 
    
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
       Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: 
         FIG.  1    is a schematic drawing of a first embodiment of a turbocharged engine system in accordance with present invention, the system of this embodiment comprises an electric compressor that is arranged to inject a compressed fluid into the exhaust subsystem of the engine upstream of the turbine of the turbocharger; 
         FIG.  2    is a schematic drawing of a second embodiment of a turbocharged engine in accordance with the present invention; the system of this embodiment comprises a check valve and a blow off valve to assist in the control of the electric compressor of the first embodiment; 
         FIG.  3    is a schematic drawing of a third embodiment of a turbocharged engine in accordance with the present invention, the system of this embodiment comprises an isolator valve and a compressor bypass valve to assist in the control of the electric compressor of the first embodiment; and 
         FIG.  4    is a flowchart depicting a method of increasing the boost pressure supplied to an internal combustion engine by a turbocharger in accordance with the present invention. 
     
    
    
       FIG.  1    of the drawings depicts a schematic drawing of the first embodiment of a turbocharged engine system  100  in accordance with present invention. 
     When the turbocharged engine system  100  of  FIG.  1    is operational, a mixture of air and fuel is supplied to an internal combustion engine  10  via an intake subsystem  12 . In this embodiment, and the subsequent embodiments, the internal combustion engine  100  is a spark-ignition engine. Other embodiments are envisaged for different types of internal combustion engine known in the art, such as compression-ignition engines. 
     The intake subsystem  12  comprises an air inlet conduit  14  with an aperture through which air is drawn into the intake subsystem  12 . This air is mixed with fuel from the gas supply  16  in the air inlet conduit  14 . The flow of fuel from the gas supply  16  to the air inlet conduit  14  is controlled by a fuel control valve  18 . The air and fuel mixture in the air inlet conduit  14  has a pressure P 1  and a temperature T 1  that can be measured by sensors (not shown) incorporated into the air inlet conduit  14 . 
     During operation, the air inlet conduit  14  supplies the air and fuel mixture to a compressor wheel  20  of a turbocharger  22 , where the mixture is compressed. The increased mass and pressure of the air and fuel mixture by the action of the compressor wheel  20  of the turbocharger  22  is known as the boost pressure or the boost. This compression of the air and fuel mixture by the compressor wheel  20  of the turbocharger  22  results in additional air being drawn into the air inlet conduit  14  as is well known in the art. 
     The intake subsystem  12  further comprises a radiator inlet conduit  24  that supplies the compressed air and fuel mixture exiting the compressor wheel  20  to a radiator  26 . The compressed air and fuel mixture in the radiator inlet conduit  24  has a pressure P 2  and temperature T 2  that can be measured by sensors (not shown) incorporated into the radiator inlet conduit  24 . The pressure P 2  of the air and fuel mixture inside the radiator inlet conduit  24  is greater than the pressure P 1  of the air and fuel mixture inside the air inlet conduit  14  due to the boost pressure imparted on the mixture by the compressor wheel  20  of the turbocharger  20 . 
     The radiator  26  cools the compressed air and fuel mixture to provide a cooled and compressed air and fuel mixture to an engine inlet conduit  28 . The cooled and compressed air and fuel mixture in the engine inlet conduit  28  has a pressure P 2 ′ and temperature T 2 ′ that can be measured by sensors (not shown) incorporated into the engine inlet conduit  28 . The radiator  26  and the engine inlet conduit  28  are part of the intake subsystem  12 . 
     The engine inlet conduit  28  channels the cooled compressed air and fuel mixture from the radiator  26  to the internal combustion engine  10 . During operation, the flow of the cooled compressed air and fuel mixture along the inlet engine conduit  26  into the internal combustion engine  10  is controlled by a throttle  30  in a manner as in known in the art. 
     During operation of the turbocharged engine system  100 , the internal combustion engine  10  combusts the cooled and compressed air fuel mixture producing mechanical power. The greater mass of air entering the engine  10  because of the action of the compressor wheel  20  of the turbocharger  22  can be used to increase the power output and/or fuel efficiency of the engine as well as reducing the emissions of certain species such as nitrous oxides NO x . 
     The combustion of the air and fuel mixture by the internal combustion engine  10  also produces waste or exhaust fluids that are expelled from the internal combustion engine  10  into the external environment via an exhaust subsystem  32 . 
     The exhaust subsystem  32  comprises an engine exhaust conduit  34  along which the exhaust fluids from the internal combustion engine  10  flow to a turbine  36  of the turbocharger  22 . The pressure P 3  and temperature T 3  of the exhaust fluid egressing the engine  10  can be measured by sensors (not shown) incorporated into the engine exhaust conduit  34 . 
     The turbine  36  is rotationally connected or coupled to the compressor wheel  20  by a turbocharger shaft  37 . Together the turbine  36 , the turbocharger shaft  37  and the compressor wheel  20  make up the turbocharger  20 . 
     The flow of the hot pressurised exhaust fluids from the engine exhaust conduit  34  rotates the turbine  36  that in turn drives the rotation of the turbocharger shaft  37  and the compressor wheel  20 . This power imbalance between the turbine  36  and the compressor wheel  20  causes it to compress the air and fluid mixture in intake subsystem  12 , increasing the air mass entering the engine  10 , as is known in the art for turbocharged engines. 
     After rotating the turbine  36 , the exhaust fluid is egressed through an exhaust conduit  38 . The exhaust conduit  38  forms part of the exhaust subsystem  32 . The pressure P 4  and temperature T 4  of the exhaust fluid within the exhaust conduit  38  can be measured by sensors (not shown) incorporated into the exhaust conduit  38 . The exhaust conduit  38  egress, or exhausts, the exhaust fluid into the environment via aftertreatment, heat recovery, noise attenuation or whatever equipment is installed downstream of the engine. 
     In accordance with the present invention, the exhaust subsystem  32  is fluidly connected with an electric compressor  40 . The electric compressor  40  comprises an electric motor  42  that rotationally drives a compressor shaft  44  that is coupled to a compressor  46 . The electric motor  42  is electrically connected to an external power source (not shown) such as the electrical grid or battery. 
     The rotation of the compressor  46  by the electric motor  42  draws in air through a compressor inlet conduit  48  and compresses it, boosting the pressure of the air. This pressure-boosted air is expelled from the compressor  46  into the compressor outlet conduit  50 . The pressure P 5  and temperature T 5  of the pressure-boosted air from the electric compressor  40  can be measured by sensors (not shown) incorporated into the compressor outlet conduit  50 . 
     The compressor outlet conduit  50  is fluidly connected to the engine exhaust conduit  34 . The pressure-boosted air from the electrical compressor  40  is injected into the exhaust conduit  34  and mixed with the exhaust fluid in the engine exhaust conduit  34  to form a mixture of exhaust fluid and air in the engine exhaust conduit  34 . The pressure P 3 ′ and temperature T 3 ′ of the exhaust fluid and air mixture can be measured by sensors (not shown) incorporated into the engine exhaust conduit  34  downstream of the fluid connection with the compressor outlet conduit  50 . When the electric compressor  40  is running, the air and exhaust fluid mix within the exhaust conduit can have a pressure P 3 ′ that is greater than would be measured if the electric compressor  40  were not installed or operational 
     By increasing the pressure P 3 ′ of the fluid entering the turbine  36  of the turbocharger  22 , the boost pressure supplied to the engine  10  is increased as the compressor wheel  20  will rotate more quickly. In this way, the amount of boost pressure, i.e. the mass of air, supplied to engine  10  can be controlled by the speed of the electric motor  42  of the electric compressor  40 . Increasing the speed of the electric motor  42  increases the pressure of air mixed with the exhaust fluid, thereby increasing the rotation of the turbocharger  22  and increasing the boost pressure supplied to the engine  10 . This can be used to accelerate the turbocharger  22  and raise the boost pressure to a desired or optimal value when the internal combustion engine  10  is starting up or experiencing a transient load event. 
       FIG.  2    and  FIG.  3    of the drawings depict schematic drawings of a second embodiment of a turbocharged engine system  200  and a third embodiment of a turbocharged engine system  300  in accordance with present invention. 
     The following features of the second embodiment and third embodiment are substantially identical in structure and function to the equivalent features of the first embodiment in  FIG.  1    and the reference numerals for these features are maintained across the embodiments and their respective figures: the internal combustion engine  10 ; the intake subsystem  12 ; the air inlet conduit  14 ; the gas supply  16 ; the fuel control valve  18 ; the compressor wheel  20 ; the turbocharger  22 ; the radiator inlet conduit  24 ; the radiator  26 ; the engine inlet conduit  28 ; the throttle  30 ; the exhaust subsystem  32 ; the engine exhaust conduit  34 ; the turbine  36 ; the turbocharger shaft  37 ; the exhaust conduit  38 ; the electric compressor  40 ; the electric motor  42 ; the compressor shaft  44 ; the compressor  46 ; the compressor inlet conduit  48 ; and compressor outlet conduit  50 . 
     The second embodiment of the turbocharged engine system  200  in  FIG.  2    and the third embodiment of the turbocharged engine system  300  in  FIG.  3    differ from the first embodiment in that they comprise valves in series or parallel with the electrical compressor  40  to assist in controlling the flow of pressure-boosted air from the electrical compressor  40  into the engine exhaust conduit  34 . 
     Referring to the second embodiment of the turbocharged engine system  200  in  FIG.  2   , the compressor outlet conduit  50  comprises a blow off valve  52  downstream of the electric compressor  40  and a check valve  54  downstream of the blow off valve  52  prior to the connection with the engine exhaust conduit  34 . 
     The blow off valve  52  is configured to vent the pressure-boosted air produced by the electric compressor  40  into the environment prior to its entry into the exhaust subsystem  32 . 
     The check valve  54  is configured to prevent the pressurized exhaust fluid in the engine exhaust conduit  34  from flowing through the compressor outlet conduit  50  towards and into the electric compressor  40 . The check valve  54  can also be configured to open when the pressure P 5  in the compressor outlet conduit  50 ; the pressure P 3  in the engine exhaust conduit  34 ; or the pressure difference between the pressure P 5  in the compressor outlet conduit  50  and the pressure P 3 ′ of the mixture of pressure-boosted air (P 5 -P 3 ′) exceeds or falls below a threshold or predetermined value. 
     In this way, the blow off valve  52  can be used to control or limit the pressure difference between the pressure P 5  and pressure P 3 ′ (P 5 -P 3 ′) supplied to the turbocharger  22  as the blow off valve  52  can be opened to vent any excess or shortfall in pressure P 5  generated by the electric compressor  40 . Another example of when the blow off valve  52  may vent pressure-boosted air is when the pressure P 3 ′ of the air and exhaust fluid mixture prior to turbine  36  of the turbocharger  22  has reached an optimal or desired value the blow off valve  52  can open to prevent the pressure P 3 ′ exceeding the desired or optimal value. A further example is when the pressure P 5  being produced by the electric compressor  40  has reached a desired or optimal value, the blow off valve  52  can open to prevent the pressure P 5  exceeding the desired or optimal value. 
     Alternatively, the blow off valve  52  can be opened to allow the electric compressor  40  to ramp up to a desired speed. By opening the blow off valve  52  while accelerating the electric motor  42 , the load on the electric motor  42  is decreased as the pressure P 5  within the compressor outlet conduit  50  is reduced due to the venting of the pressure-boosted air. This means that the electric motor  42  can accelerate to the desired or optimal speed more quickly and once the desired compressor  46  speed has been achieved, the blow off valve  52  can then be shut and the pressure-boosted air supplied to the turbocharger  22  via the engine exhaust conduit  34  when the check value  54  is open or opened. This will provide even more aggressive turbocharger speed increases at the early part of the transient and thus further improve the engine  10  load acceptance capability. 
     Referring to the third embodiment of the turbocharged engine system  300  in  FIG.  3   , the compressor outlet conduit  50  comprises an isolator valve  56  downstream of the electric compressor  40  prior to the connection with the engine exhaust conduit  34 . The turbocharged engine system  300  further comprises a bypass conduit  58  that is connected between the compressor inlet conduit  48  and compressor outlet conduit  50  in parallel with the electric compressor  40 . The bypass conduit  58  comprises a compressor bypass valve  60 . 
     The isolator valve  56  is configured to control the flow of pressure-boosted air from the electric compressor  40  into the exhaust subsystem  32 . The isolator valve  56  can do this by occluding the compressor outlet conduit  50  partially or completely, thereby limiting the injection of pressure-boosted air form the compressor  40 . In this way, the pressure P 3 ′ of the air and fuel mixture prior to entry into the turbine  36  of turbocharger can be controlled. For example, this can be used to ramp up the electric motor  42  to a desired speed prior to opening. Further, the occlusion of the compressor outlet conduit  50  by the isolator valve  56  can prevent flow of the exhaust fluid from the exhaust subsystem  32  into or towards the electric compressor  40 . 
     The bypass valve  60  is configured to vent the pressure-boosted air produced by the electric compressor  40  back to the inlet of the electric compressor  42  prior to its entry into the exhaust subsystem  32 . For example, the bypass valve  60  can open to prevent pressure building up within the compressor outlet conduit  50  when the isolator valve  56  partially or completely occludes the compressor outlet conduit  50 , such as when the isolator valve  56  is shut and the electric motor  42  is ramping up to a desired speed. Alternatively, the bypass valve  60  can be actuated to relieve pressure or increase the flow through the electric compressor  40  as it approaches its surge line. The electric compressor  40  will approach its surge line when the isolator valve  56  (or the check valve  54 in the second embodiment) is closed and the electric compressor  40  is still spinning, or when the pressure at P 3 ′ is equal to or close to being equal to P 5  such that the flow of air through the electric compressor  40  will naturally decrease. 
     An immediate injection of pressure-boosted air can be supplied by closing the isolator valve  56  and opening the bypass valve  60  while the electric compressor  40  is running. During this time, the electric compressor  40  can be ramped or spun up to a desired, or maximum, speed raising the pressure P 5  of the pressure-boosted air to a desired, or maximum, value. When a load increase occurs on or is requested by the internal combustion engine  10 , the isolator valve  56  can then be opened and the bypass valve  60  closed. This causes an instantaneous injection of pressure-boosted air from the electric compressor  40  into the exhaust subsystem  32 . The instantaneous injection rapidly accelerates the turbocharger  22  and rapidly increases the boost pressure, enabling rapid load acceptance by the internal combustion engine  10 . 
     Other embodiments are envisaged where a turbocharged engine system comprises alone or combination any of the blow-off valve of the second embodiment, the check valve of the second embodiment, the isolator valve of the third embodiment and the bypass valve of the third embodiment. 
       FIG.  4    of the drawings depicts a method of increasing the boost pressure supplied to the internal combustion engine  10  by a turbocharger  22  using the turbocharged engine systems  100 ,  200 ,  300  of  FIG.  1   ,  FIG.  2    and  FIG.  3   . 
     The method begins with the electric compressor  40  producing a stream of compressed fluid in step S 1 . The stream of compressed fluid, typically air, is produced by the action of the compressor  46  being rotated by the electric motor  42 . The pressure P 5 , mass and flow of the compressed fluid is therefore controlled by the speed of the electric motor  42 . 
     This stream of compressed fluid is then injected or added into the exhaust stream from the internal combustion engine in step S 2 . The stream of compressed fluid form the electric compressor  40  and exhaust stream mix within the engine exhaust conduit  34  to produce a pressure-boosted exhaust stream. 
     This pressure-boosted exhaust stream can then accelerate the turbine  36  of the turbocharger  22  in step S 3 , which causes the turbocharger  22  to supply a great boost pressure to the internal combustion engine  10 . 
     Subsequently in step S 4 , the amount, or mass flow, of the pressure-boosted air being injected into the exhaust subsystem is increased, maintained or decreased. The change or maintenance of the production of the pressure-boosted air is typically made in reference to the boost pressure and the engine load by controlling the speed of the electric compressor  40  or by actuating the isolator valve  56 , bypass valve  60 , check valve  54  and/or blow-off valve  52  as is described above for the first, second and third embodiments.