Abstract:
A method of switching a combustion mode of a diesel engine may include determining a carbon dioxide concentration in an intake manifold of a diesel engine, operating the diesel engine in a first combustion mode, and operating the diesel engine in a second combustion mode when the determined carbon dioxide concentration is greater than a predetermined carbon dioxide concentration value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/966,864, filed on Aug. 30, 2007. 
     This application is related to U.S. patent application Ser. No. 11/466,902 filed on Aug. 24, 2006. The disclosures of the above applications are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to engine control systems for vehicles, and more specifically to combustion mode control systems for diesel engines. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Diesel engines may be operated in a conventional combustion mode and a Premixed Compression Ignition (PCI) combustion mode. PCI is an advanced diesel combustion technique that may reduce diesel engine emissions. With PCI, fuel is injected into the combustion chamber of the cylinder much earlier in the combustion stroke than would be done for conventional diesel combustion. The desired fuel amount is supplied significantly before the piston reaches the compression top dead center (TDC). The early injected fuel is mixed sufficiently with the air before the piston reaches the compression TDC. Thus, the technique provides a lean and well mixed state of air/fuel mixture before ignition. 
     A diesel engine may be switched from a conventional combustion mode to PCI combustion mode during low-load operating conditions. Therefore, engine load conditions may be monitored to ensure that the combustion mode is switched to PCI combustion mode at low load conditions. However, switching to PCI combustion mode even at low engine load conditions may result in high NOx emissions without appropriate combustion gas conditions. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     SUMMARY 
     Accordingly, a method of switching a combustion mode of a diesel engine may include determining a carbon dioxide concentration in an intake manifold of a diesel engine, operating the diesel engine in a first combustion mode, and operating the diesel engine in a second combustion mode when the determined carbon dioxide concentration is greater than a predetermined carbon dioxide concentration value. 
     A control module for switching a combustion mode of a diesel engine may include a carbon dioxide concentration determination module and a combustion mode switching module. The carbon dioxide concentration determination module may be configured to determine a concentration of carbon dioxide in an intake manifold of the diesel engine. The combustion mode switching module may be in communication with the carbon dioxide concentration determination module and may be configured to switch operation of the diesel engine between first and second combustion modes based on the determined concentration of carbon dioxide from the carbon dioxide concentration determination module. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of a vehicle according to the present disclosure; 
         FIG. 2  is a control block diagram of the control module shown in  FIG. 1 ; 
         FIG. 3  is a flow diagram illustrating steps for determining switching from a conventional diesel combustion mode to a PCI combustion mode according to the present disclosure; and 
         FIG. 4  is a flow diagram illustrating steps for determining switching from a PCI combustion mode to a conventional diesel combustion mode according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
     Referring to  FIG. 1 , an exemplary vehicle  10  is schematically illustrated. Vehicle  10  may include a diesel engine  12  in communication with an intake system  14 , an exhaust system  16 , a fuel system  18  and an exhaust gas recirculation (EGR) system  20 . Intake system  14  may include an intake manifold  22  and a throttle  24 . Throttle  24  may control an air flow into engine  12  and fuel system  18  may control a fuel flow into engine  12 . Exhaust gas created by combustion of the air/fuel mixture may exit engine  12  through exhaust system  16 . Exhaust system  16  may include an exhaust manifold  26  in communication with a catalyst  28  and a diesel particulate filter (DPF)  30 . 
     EGR system  20  may provide selective communication between intake system  14  and exhaust system  16 . EGR system  20  may include an EGR valve  32  and an EGR line  34 . EGR valve  32  may be mounted on intake manifold  22  and EGR line  34  may extend from exhaust manifold  26  to EGR valve  32  providing communication between exhaust manifold  26  and EGR valve  32 . Additionally, engine  12  may include a turbocharger (not shown). The turbocharger may be in communication with both the exhaust system  16  and intake system  14 . The turbocharger may be driven by the exhaust system  16  and may provide an increased airflow rate to intake system  14 . 
     Vehicle  10  may further include a control module  36  in communication with fuel system  18 , throttle  24  and EGR valve  32 . Control module  36  may additionally be in communication with a mass air flow (MAF) sensor  38 , an intake manifold pressure sensor  40 , and an exhaust manifold pressure sensor  42 . 
     MAF sensor  38  provides a signal to control module  36  indicative of the air flow rate into intake manifold  22 . Intake manifold pressure sensor  40  provides a signal to control module  36  indicative of the air pressure in intake manifold  22  and exhaust manifold pressure sensor  42  provides a signal to control module  36  indicative of the air pressure in exhaust manifold  26 . 
       FIG. 2  depicts that control module  36  may include a load determination module  44 , a carbon dioxide (CO 2 ) concentration determination module  46 , a combustion mode switching module  48 , an air control module  50 , a fuel control module  52 , and an EGR module  54 . Load determination module  44  may be in communication with combustion mode switching module  48  and may provide information regarding a load on engine  12 , as discussed below. CO 2  concentration determination module  46  may be in communication with combustion mode switching module  48  and may provide information regarding a CO 2  concentration in intake manifold  22 , as discussed below. Combustion mode switching module  48  may be in communication air and fuel control modules  50 ,  52  and EGR module  54 , and may provide information regarding the desired combustion mode for operation of engine  12 , as discussed below. Air and fuel control modules  50 ,  52  may control the mass air flow and fuel injection into engine  12  based on the operating combustion mode of engine  12 . EGR module  54  may control an amount of exhaust gas flow provided to intake manifold  22  based on the operating combustion mode of engine  12 . 
       FIG. 3  depicts a control logic  100  for switching from a conventional diesel combustion mode to a PCI combustion mode. Control logic  100  may begin at determination block  102  where an engine load is determined by load determination module  44 . The engine load may generally be based on an engine speed and an amount of fuel injected into engine  12 . Once the engine load is determined, control logic  100  may proceed to decision block  104 . Decision block  104  evaluates whether the determined engine load is below a predetermined limit using combustion mode switching module  48 . If the determined engine load is less than the predetermined limit, control logic  100  proceeds to determination block  106 . However, if the load is not below the predetermined limit, engine  12  may not switch to PCI combustion mode, and control logic  100  returns to determination block  102 . 
     Determination block  106  determines the CO 2  concentration in intake manifold  22  using CO 2  concentration determination module  46 . CO 2  concentration may be determined in a variety of ways including using a CO 2  sensor and calculating a CO 2  concentration level. A calculated CO 2  concentration may be based on a CO 2  concentration in the air entering intake manifold  22 , a CO 2  concentration in the engine exhaust gas, an EGR percentage, and a fuel quantity supplied to fuel system  18 . The EGR percentage may be controlled by EGR module  54  and may be based on the operating combustion mode of engine  12 . For example, operation of engine  12  in PCI combustion mode may include a higher EGR percentage than operation in the conventional combustion mode. EGR percentage may generally be defined as the percentage of the total mass flow into engine  12  that EGR accounts for. When operating in PCI combustion mode, EGR percentage may be up to seventy percent. Once the CO 2  concentration is determined, control logic  100  proceeds to decision block  108 . 
     Decision block  108  evaluates whether the CO 2  concentration is greater than a predetermined limit using combustion mode switching module  48 . If the CO 2  concentration is greater than the predetermined limit, control logic  100  proceeds to control block  110 . However, if the CO 2  concentration is not above the predetermined limit, control returns to determination block  102 . Control block  110  switches engine  12  from conventional diesel combustion mode to a PCI combustion mode using combustion mode switching module  48 . Control logic  100  may then terminate and proceed to control logic  200 , as discussed below. 
       FIG. 4  depicts a control logic  200  for switching from a PCI combustion mode to a conventional combustion mode. Control logic  200  may begin at determination block  202  where an engine load is determined by load determination module  44 . Control logic  200  may then proceed to decision block  204  where the determined engine load is evaluated using combustion mode switching module  48 . If the determined engine load is less than a predetermined limit, control logic  200  may proceed to determination block  206 . However, if the determined engine load is not below the predetermined limit, control logic  200  may proceed to control block  210 , as discussed below. 
     Determination block  206  may determine the CO 2  concentration in intake manifold  22  using CO 2  concentration determination module  46 , as discussed above. Control logic  200  may then proceed to decision block  208 . Decision block  208  determines whether the CO 2  concentration is greater than a predetermined limit using combustion mode switching module  48 . If the CO 2  concentration is greater than the predetermined limit, control logic  200  returns to determination block  202 . However, if the CO 2  concentration is not greater than the predetermined limit, control logic  200  proceeds to control block  210 . Control block  210  switches from PCI combustion mode to conventional combustion mode using combustion mode switching module  48 . Control logic  200  may then terminate and proceed to control logic  100 , as discussed above. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.