Abstract:
A method for determining cylinder blow-through air via engine volumetric efficiency is disclosed. In one example, the method provides a way to adjust cylinder blow-through to promote and control a reaction in an exhaust after treatment device. The approach may simplify cylinder blow-through calculations and improve engine emissions via providing improved control of constituents reaching an exhaust after treatment device.

Description:
BACKGROUND/SUMMARY 
       [0001]    Turbocharged and supercharged engines pressurize air entering an engine so that engine power can be increased. The pressurized air provides for an increased cylinder air charge during a cycle of the engine as compared to a naturally aspirated engine. Further, the cylinder fuel charge can be increased as the cylinder air charge is increased to increase the amount of energy produced when the fuel is combusted with the air during a cycle of the cylinder. However, during periods of valve overlap where both intake and exhaust valves of a cylinder are simultaneously open, it is possible for air to pass directly from the engine intake manifold to the engine exhaust manifold without participating in combustion within a cylinder. Air passing directly from the intake manifold to the exhaust manifold without participating in combustion may be referred to as blow-through. 
         [0002]    Fresh air or blow-through passing through the intake manifold to the exhaust manifold may have beneficial as well as undesirable characteristics. For example, blow-through can evacuate internal exhaust residuals from engine cylinders so that the fresh charge in the cylinder increases, thereby increasing engine power output. However, blow-through may also upset a delicate balance between oxygen, hydrocarbons, and CO in a catalyst in the engine exhaust path. If blow-through provides excess oxygen to the catalyst, it may be possible for NOx conversion efficiency to decrease. 
         [0003]    One way to mitigate engine emissions that may result from blow-through is to account for blow-through gases. In one example, engine air-fuel ratio may be richened so that on average a stoichiometric air-fuel ratio mixture passes through engine cylinders. For example, for a direct injection engine where fuel is injected after exhaust valve closing, fresh air can flow from the intake manifold to the exhaust manifold during intake and exhaust overlap. Further, an increased amount of fuel may be supplied to an engine cylinder so that the cylinder combusts a rich air-fuel mixture. The contents of the cylinder may be subsequently combined with the blow-through air stored in the catalyst to provide near stoichiometric ratios of gases to the catalyst so that the catalyst can efficiently oxidize and reduce undesirable exhaust gas constituents. However, it is difficult to keep the catalyst balanced and adjust air-fuel ratio of a cylinder without knowing the amount of blow-through for speed-density control systems. 
         [0004]    The inventors herein have recognized the above-mentioned disadvantages and have developed a method for accounting for cylinder blow-through of an engine, comprising: adjusting an engine actuator controlling supply of a constituent for combustion to a cylinder of the engine in response to a difference between a total cylinder air mass flow curve and a volumetric efficiency curve. 
         [0005]    A mass of oxygen that reaches an exhaust after treatment device resulting from cylinder blow-through may be determined from two curves that characterize engine breathing. In particular, cylinder blow-through may be determined as a difference between a first curve that represents volumetric efficiency for a theoretical maximum cylinder air charge and second curve that represents total air flow through the cylinder. Both curves may be described according to slopes of lines so that cylinder blow-through may be determined without having to perform a significant number of calculations and without having to determine a cylinder air-fuel ratio. 
         [0006]    In another example, the amount of blow-through can be adjusted to increase engine output and to provide a desired amount of oxygen to the exhaust system to promote regeneration of an exhaust gas emissions device. For example, blow-through may be used during regeneration of a particulate filter to oxidize stored carbonaceous soot. The amount of blow though can affect the temperature rise of the oxidizing carbonaceous shoot during regeneration. Therefore, it may be desirable to determine the amount of blow though so that a desired level of blow-though may be provided to the emissions device without supplying excess blow-through. 
         [0007]    The present description may provide several advantages. In particular, the approach can reduce vehicle emissions by providing an accurate blow-through estimate so that an amount of air reaching an exhaust gas after treatment device may be determined. Further, an engine actuator may be adjusted so as to control the amount of blow-through supplied to the exhaust gas after treatment device. Further still, the method provides for determining an engine operating condition where blow-through begins so that blow-though can be controlled during conditions where increased engine power is desired or when exhaust gas constituents entering a catalyst may be balanced so as to improve conversion efficiency of engine exhaust emissions. 
         [0008]    The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
         [0009]    It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0010]      FIG. 1  shows a schematic depiction of an engine; 
           [0011]      FIG. 2  shows a volumetric efficiency characterization of cylinder air charge; 
           [0012]      FIG. 3  shows a high level flowchart of a method for determining cylinder blow-through and making adjustments to compensate for cylinder blow-through. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The present description is directed to determining blow-through of a cylinder of an engine.  FIG. 1  shows one example system for determining blow-through of a cylinder. The system includes a turbocharger operated with a spark ignited mixture of air and gasoline, alcohol, or a mixture of gasoline and alcohol. However, in other examples the engine may be a compression ignition engine, such as a diesel engine.  FIG. 2  shows a simulated example plot of curves that are the basis for determining cylinder blow-through.  FIG. 3  shows an example method for determining and adjusting cylinder blow-through. 
         [0014]    Referring to  FIG. 1 , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1 , is controlled by electronic engine controller  12 . Engine  10  includes combustion chamber  30  and cylinder walls  32  with piston  36  positioned therein and connected to crankshaft  40 . Combustion chamber  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Each intake and exhaust valve may be operated by an intake cam  51  and an exhaust cam  53 . Alternatively, one or more of the intake and exhaust valves may be operated by an electromechanically controlled valve coil and armature assembly. The position of intake cam  51  may be determined by intake cam sensor  55 . The position of exhaust cam  53  may be determined by exhaust cam sensor  57 . 
         [0015]    Fuel injector  66  is shown positioned to inject fuel directly into cylinder  30 , which is known to those skilled in the art as direct injection. Alternatively, fuel may be injected to an intake port, which is known to those skilled in the art as port injection. Fuel injector  66  delivers liquid fuel in proportion to the pulse width of signal FPW from controller  12 . Fuel is delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Fuel injector  66  is supplied operating current from driver  68  which responds to controller  12 . In addition, intake manifold  44  is shown communicating with optional electronic throttle  62  which adjusts a position of throttle plate  64  to control air flow from intake boost chamber  46 . 
         [0016]    Exhaust gases spin turbocharger turbine  164  which is coupled to turbocharger compressor  162  via shaft  161 . Compressor  162  draws air from air intake  42  to supply boost chamber  46 . Thus, air pressure in intake manifold  44  may be elevated to a pressure greater than atmospheric pressure. Consequently, engine  10  may output more power than a normally aspirated engine. In other examples, compressor  162  may be a supercharger driven by the engine where turbine  164  is omitted. 
         [0017]    Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Ignition system  88  may provide a single or multiple sparks to each cylinder during each cylinder cycle. Further, the timing of spark provided via ignition system  88  may be advanced or retarded relative to crankshaft timing in response to engine operating conditions. 
         [0018]    Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of exhaust gas after treatment device  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . In some examples, exhaust gas after treatment device  70  is a particulate filter and/or a three-way catalyst. In other examples, exhaust gas after treatment device  70  is solely a three-way catalyst. 
         [0019]    Controller  12  is shown in  FIG. 1  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only memory  106 , random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  134  coupled to an accelerator pedal  130  for sensing accelerator position adjusted by foot  132 ; a knock sensor for determining ignition of end gases (not shown); a measurement of engine manifold pressure (MAP) from pressure sensor  121  coupled to intake manifold  44 ; a measurement of boost pressure from pressure sensor  122  coupled to boost chamber  46 ; an engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position; a measurement of air mass entering the engine from sensor  120  (e.g., a hot wire air flow meter); and a measurement of throttle position from sensor  58 . Barometric pressure may also be sensed (sensor not shown) for processing by controller  12 . In a preferred aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. 
         [0020]    In some embodiments, the engine may be coupled to an electric motor/battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, series configuration, or variation or combinations thereof. Further, in some embodiments, other engine configurations may be employed, for example a diesel engine. 
         [0021]    During operation, each cylinder within engine  10  typically undergoes a four stroke cycle: the cycle includes the intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valve  54  closes and intake valve  52  opens. Air is introduced into combustion chamber  30  via intake manifold  44 , and piston  36  moves to the bottom of the cylinder so as to increase the volume within combustion chamber  30 . The position at which piston  36  is near the bottom of the cylinder and at the end of its stroke (e.g. when combustion chamber  30  is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). During the compression stroke, intake valve  52  and exhaust valve  54  are closed. Piston  36  moves toward the cylinder head so as to compress the air within combustion chamber  30 . The point at which piston  36  is at the end of its stroke and closest to the cylinder head (e.g. when combustion chamber  30  is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means such as spark plug  92 resulting in combustion. During the expansion stroke, the expanding gases push piston  36  back to BDC. Crankshaft  40  converts piston movement into a rotational torque of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve  54  opens to release the combusted air-fuel mixture to exhaust manifold  48  and the piston returns to TDC. Note that the above is described merely as an example, and that intake and exhaust valve opening and/or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. 
         [0022]    Referring now to  FIG. 2 , a simulated plot of volumetric efficiency characterization of cylinder air charge is shown. The X axis of plot  200  represents air mass charge of a cylinder per cylinder intake event or cylinder cycle. Air mass charge increases from the left side of the plot to the right side of the plot. The Y axis of plot  200  represents engine intake manifold absolute pressure (MAP) and MAP increase from the bottom of the origin of the plot in a direction of the Y axis. 
         [0023]    Curve  202  represents the theoretical maximum air charge that the cylinder can hold at a given pressure at intake valve closing (IVC). Thus, the cylinder mass charge increases linearly as the cylinder pressure increases. In one example, the maximum air charge that the cylinder can hold may be characterized as a slope of a line where the slope is described as: 
         [0000]    
       
         
           
             Slope 
             = 
             
               1 
               
                 
                   ( 
                   
                     1 
                     - 
                     
                       r 
                       pb 
                     
                   
                   ) 
                 
                  
                 
                   c 
                   norm 
                 
               
             
           
         
       
     
         [0000]    where variable c norm  accounts for physical properties of air, intake manifold temperature, and cylinder displacement. Variable r pb  is an effective pushback ratio characterizing a portion of a cylinder mixture that may be pushed into the engine intake manifold from the cylinder as the piston moves in a direction toward the cylinder head while the intake valve is open. The pushback ratio may be determined as the greater of a constant multiplied by the physical ratio of cylinder volume displaced by the piston moving from the bottom dead center (BDC) to the intake valve closing (IVC) point, to the total cylinder displacement volume of the cylinder and the pushback ratio computed from engine mapping as: 
         [0000]    
       
         
           
             1 
             - 
             
               1 
               
                 
                   c 
                   norm 
                 
                 * 
                 air_slope 
               
             
           
         
       
     
         [0000]    where air_slope is the least-squares linear fit of the manifold pressure vs. trapped air charge data excluding blow-through data points. 
         [0024]    Curve  204  represents a conventional non-blow-through (e.g., conditions where blow-through is not present) volumetric regression curve in which both x and y axes have been scaled by ExhMAP/ExhMAP_nom. Where ExhMAP is exhaust manifold absolute pressure and where ExhMAP_nom is a nominal exhaust manifold absolute pressure (e.g. at sea level). Instead of the cycle average exhaust manifold absolute pressure, an average over the valve-overlap window, or some other related quantity, could be used for scaling. In engines having variable cam timing, curve  204  may be regressed from data points such as  220  into a quadratic curve. 
         [0025]    Intersection  208  represents the point where the conventional non-blow-through curve  204  and the theoretical maximum air charge curve  202  intersect. Thus, when MAP is greater than the level of MAP where intersection  208  takes place, air blows through the cylinder. In some examples, the engine may be operated at a MAP up to where intersection  208  occurs but not higher so that cylinder blow-through may be prevented. In other examples, when MAP is higher than MAP where intersection  208  takes place, blow-through may be determined so that an actuator may compensate for the amount of blow-through. 
         [0026]    Curve  210  represents a total amount of air flowing through the cylinder during the blow through operation. The total amount of air includes air in the cylinder as well as blow-through air. In one example, curve  210  may be described by a slope that extends from intersection  208 . The slope may be found via regressing empirically determined data. For example, a least-squares or other regression may be the basis for determining the equation of a line describing total air flow through a cylinder during blow-through conditions. 
         [0027]    Given the cylinder air charge m air   cyl , the inferred pressure in the intake manifold as shown in  FIG. 2  may be described as: 
         [0000]                                                                            m   air   x          (   k   )       =           m   air   cyl          (   k   )         vol_eff      _cor        (     ACT   ,   ECT     )         *       30        [     in   -   Hg     ]           P   exh          (   k   )                               if m air   x (k) &gt; m c (k)                                    P   inf          (   k   )       =     
                P   exh          (   k   )         30        [     in   -   Hg     ]            max        {         1     c   norm       *       m   c          (   k   )         ,     [         1     c   norm       *       m   c          (   k   )         +     slp   *     (         m   air   x          (   k   )       -       m   c          (   k   )         ]         }                                    else                                    P   inf          (   k   )       =     
                P   exh          (   k   )         30        [     in   -   Hg     ]              (     air_offset   +     air_slope   ×       m   air   x          (   k   )         +     air_quad   ×         m   air   x          (   k   )       2         )                                end                    
Where k is a k th  sample interval, m air   cyl  (k) is mass of air in cylinder, m c  (k) is mass of air in cylinder at the point blow-through begins (e.g.,  208 ), slp is the slope of the line describing total amount of air flowing through the cylinder (e.g.,  210 ), P exh  (k) is exhaust pressure, vol_eff_cor (ACT, ECT) is a volumetric correction for air charge temperature ACT and engine temperature ECT, and m air   x  is the scaled cylinder air charge. The parameters air_offset, air_slope, and air_quad represent the conventional non-blow-through curve  204  and can be calibrated by a least squares fit of the engine data.
 
         [0028]    To compute the trapped cylinder air charge and the mass of blow-through air for a given manifold absolute pressure MAP, a recursive calculation can be used. At time k, the cylinder air charge is computed from the current measurement of MAP and one of the previously computed estimates of the mass of dilution: 
         [0000]        m   air   cyl ( k )=(1 −r   pb )* chd norm *MAP( k )− m   d ( k−b  1   )
 
         [0000]    where an d  is the estimated mass of dilution in the cylinder “l” events before (l is equal to 1 for an I4 engine, 1.5 for a V6, and 2 for a V8). Next, the inferred manifold absolute pressure is computed as above while assuming operation in the non-blow-through condition: 
         [0000]    
       
         
           
             
                 
             
              
             
               
                 
                   m 
                   air 
                   x 
                 
                  
                 
                   ( 
                   k 
                   ) 
                 
               
               = 
               
                 
                   
                     
                       m 
                       air 
                       cyl 
                     
                      
                     
                       ( 
                       k 
                       ) 
                     
                   
                   
                     vol_eff 
                      
                     _cor 
                      
                     
                       ( 
                       
                         ACT 
                         , 
                         ECT 
                       
                       ) 
                     
                   
                 
                 * 
                 
                   
                     30 
                      
                     
                       [ 
                       
                         in 
                         - 
                         Hg 
                       
                       ] 
                     
                   
                   
                     
                       P 
                       exh 
                     
                      
                     
                       ( 
                       k 
                       ) 
                     
                   
                 
               
             
           
         
       
       
         
           
             
               
                 P 
                 inf 
               
                
               
                 ( 
                 k 
                 ) 
               
             
             = 
             
               
                 
                   
                     P 
                     exh 
                   
                    
                   
                     ( 
                     k 
                     ) 
                   
                 
                 
                   30 
                    
                   
                     [ 
                     
                       in 
                       - 
                       Hg 
                     
                     ] 
                   
                 
               
                
               
                 ( 
                 
                   air_offset 
                   + 
                   
                     air_slope 
                     × 
                     
                       
                         m 
                         air 
                         x 
                       
                        
                       
                         ( 
                         k 
                         ) 
                       
                     
                   
                   + 
                   
                     air_quad 
                     × 
                     
                       
                         
                           m 
                           air 
                           x 
                         
                          
                         
                           ( 
                           k 
                           ) 
                         
                       
                       2 
                     
                   
                 
                 ) 
               
             
           
         
       
     
         [0000]    The current estimate of the mass of dilution in the cylinder is: 
         [0000]        m   d ( k )=max {0 , c   norm *(1 −r   pb )* P   inf ( k )− m   air   cyl ( k )}
 
         [0000]    If the computed mass of dilution is 0, the air charge computed above is higher than the critical value m c , which means the engine is operating in blow-through. In this case the in-cylinder air charge is clipped to: 
         [0000]        m   air   cyl ( k )=(1 −r   pb )* c   norm *MAP( k ) 
         [0029]    The amount or mass of blow-through may be determined for a desired or given MAP via taking a difference between curve  210  and curve  202  as represented by the distance  250 . Thus, blow-through may be determined according to volumetric efficiency characterization of an engine: 
         [0000]    
       
         
           
             
               
                 m 
                 air 
                 bt 
               
                
               
                 ( 
                 k 
                 ) 
               
             
             = 
             
               max 
                
               
                 { 
                 
                   0 
                   , 
                   
                     
                       
                         ( 
                         
                           
                             1 
                             / 
                             
                               c 
                               norm 
                             
                           
                           - 
                           
                             slp 
                             bt 
                           
                         
                         ) 
                       
                       × 
                       
                         [ 
                         
                           
                             
                               m 
                               air 
                               x 
                             
                              
                             
                               ( 
                               k 
                               ) 
                             
                           
                           - 
                           
                             
                               m 
                               c 
                             
                              
                             
                               ( 
                               k 
                               ) 
                             
                           
                         
                         ] 
                       
                     
                     
                       slp 
                       bt 
                     
                   
                 
                 } 
               
               × 
               
                 
                   
                     P 
                     exh 
                   
                    
                   
                     ( 
                     k 
                     ) 
                   
                 
                 
                   30 
                    
                   
                     [ 
                     inHg 
                     ] 
                   
                 
               
               × 
               
                 
                   560 
                   
                     ACT 
                     + 
                     460 
                   
                 
               
             
           
         
       
     
         [0030]    Finally the total amount of air is equal to the sum of the in-cylinder air-charge m air   cyl  and the mass of blow through m air   bt . 
         [0031]    Referring now to  FIG. 3 , a high level flowchart of a method for determining cylinder blow-through and compensating for cylinder blow-through is shown. The method of  FIG. 3  is executable via instructions of a controller as shown in the system of  FIG. 1 . 
         [0032]    At  302 , method  300  determines engine operating conditions. Engine operating conditions may include but are not limited to engine temperature, ambient air temperature, MAP, engine air flow, throttle position, engine torque demand, and cam positions. Method  300  proceeds to  304  after engine operating conditions are determined. 
         [0033]    At  304 , method  300  characterizes a non-blow-through curve of an engine in a MAP/Air charge plane as shown via curve  204  of  FIG. 2 . In one example, values of MAP and cylinder air charge are determined at steady state (e.g., steady engine speed and torque demand) engine operating conditions. An equation of a curve is identified from the MAP and cylinder air charge data points via a least-squares or other type of regression. The curve may also be scaled via a ratio of exhaust pressure versus nominal exhaust pressure. The equation of the curve may be stored in controller memory such that cylinder air charge or MAP may be determined when the equation of the curve is indexed or multiplied by a present value of MAP or cylinder air charge. Method  300  proceeds to  308  after non-blow-through volumetric efficiency is characterized. 
         [0034]    At  308 , method  300  determines a maximum volumetric efficiency of the cylinder or maximum air charge that the cylinder can hold at a give pressure. In one example, the maximum volumetric efficiency is determined at IVC. The maximum air charge that the cylinder can hold as described above may be characterized as a slope of a line where the slope is described as: 
         [0000]    
       
         
           
             Slope 
             = 
             
               1 
               
                 
                   ( 
                   
                     1 
                     - 
                     
                       r 
                       pb 
                     
                   
                   ) 
                 
                  
                 
                   c 
                   norm 
                 
               
             
           
         
       
     
         [0000]    The slope may be stored in controller memory and indexed at a later time to determine MAP or cylinder air charge. For example, when the slope is multiplied by a desired cylinder air charge, an intake manifold pressure that provides the desired cylinder air charge is output. Similarly, cylinder air charge may be determined via multiplying 1/slope by MAP to determine cylinder air charge. Method  300  proceeds to  310  after maximum volumetric efficiency of the engine is determined. 
         [0035]    At  310 , method  300  determines a total mass of air through the engine during blow-through conditions. In one example as described above, the total amount of air passing through an engine cylinder and MAP may be empirically determined via monitoring MAP and mass air flow through an engine after the blow-through point  208  is determined. The blow-through point  208  may be determined as the intersection of the non-blow-through volumetric efficiency curve and the maximum volumetric efficiency curves as is described above. The blow-through point may be determined and stored in memory so that engine blow-through may be easily determined during engine operation, or it may be computed on-line while the engine is running. Method  300  proceeds to  312  after the total mass of air through the engine is determined. One possible way to calculate trapped cylinder air amount and the blow-through air mass is described above. 
         [0036]    At  312 , cylinder air charge is determined. In one example, cylinder air charge may be determined via selecting the lower value of cylinder air charge from the non-blow-through curve (e.g., curve  204  of  FIG. 2 ) and the cylinder air charge from the theoretical maximum air charge that the cylinder can hold (e.g., curve  202  of  FIG. 2 ) at a given MAP. Alternatively, a MAP where a desired cylinder air charge is provided may be determined via selecting the higher value of MAP from the non-blow-through curve and the theoretical maximum air charge curve. In this way, depending on the sensor set available and the objectives, either MAP or cylinder air charge may be determined. Method  300  proceeds to  314  after cylinder air charge is determined. 
         [0037]    At  314 , method  300  determines blow-through via the total mass flow through the cylinder and the maximum volumetric efficiency curves. In one example, the flow at the maximum volumetric efficiency of the cylinder is subtracted from the total mass flow through the cylinder to provide an amount of cylinder blow-through. An amount of engine blow-through may be determined via summing blow-through amounts of each engine cylinder over one or more engine cycles. In one example, as shown in  FIG. 2 , the blow-through may be visually represented as shown at  250  of  FIG. 2 . Method  300  proceeds to  316  after blow-through is determined. 
         [0038]    At  316 , total cylinder air charge may be determined via adding cylinder air charge from  312  and blow-through from  314 . Alternatively, total cylinder air charge may be determined via simply indexing the total air mass curve as described at  310  and  FIG. 2 . Method  300  proceeds to  318  after the total cylinder air charge is determined. 
         [0039]    At  318 , method  300  adjusts engine operation based on cylinder air charge, blow-through, and total cylinder air flow. Spark timing and air-fuel ratio for a cylinder may be determined via indexing a spark map via the present cylinder air charge. For example, if cylinder air charge is X lbm/stroke engine spark may be determined to be 30 crankshaft degrees before top dead center compression stroke. Further, injector and cam timing may be adjusted based on cylinder air charge via similarly indexing tables of empirically determined injector timings and cam timing using the present cylinder air charge. Further, in some examples, MAP, throttle position, compressor or supercharger controls and/or variable valve timing controls may be adjusted to provide a desired cylinder air charge via indexing tables of empirically determined values that are indexed via cylinder air charge. 
         [0040]    Injector timing and pulse width may also be adjusted for blow-through. In one example, an injected fuel amount can be adjusted proportionately with blow-through via adjusting fuel injector pulse width. For example, if blow through is X lbm/event a fuel pulse width may be adjusted so that X*1/14.6 lbm/event of fuel is added to each cylinder during a cylinder cycle so as to balance air and fuel reaching the catalyst. 
         [0041]    In another example, a position of a throttle can be adjusted based on the pressure drop across the throttle and the desired cylinder air flow rate to provide a MAP that provides the cylinder flow rate. 
         [0042]    In another example, throttle position and turbocharger vane or waste gate position can be adjusted to adjust boost and MAP so that a desired amount of blow-through is provided. For example, if a predetermined amount of blow-through is desired, the predetermined amount of blow-through may be determined via subtracting the maximum volumetric efficiency curve from the total amount of air flowing through the cylinder at MAP values greater than a point where blow-through begins (e.g.,  208  of  FIG. 2 ). Engine boost may be increased along with adjusting throttle position such that the lowest value of MAP where the desired level of blow-through is present is provided. In one example, the waste gate may be closed to increase boost pressure and the throttle opened to increase MAP to a level where a desired amount of blow-through is present. Alternatively, if MAP is higher than where a desired blow-through is provided (e.g., blow-through is greater than is desired), then the throttle may be closed and the boost reduced via opening a turbocharger waste gate. In some cases, the amount of blow-through can be lowered by opening the compressor bypass valve or increased by engaging a supercharger, if the engine is so equipped. Further, in some examples intake and exhaust valve opening time overlap may be increased to provide a desired level of blow-through. Thus, blow-through can be adjusted to increase or decrease an amount of energy, oxygen, or other exhaust gas constituents supplied to an emissions device in an exhaust system. 
         [0043]    Some engine actuators may also be adjusted based on the total cylinder flow. For example, the amount of fuel injected to the engine may be adjusted based on the total flow of air through engine cylinders. Thus, different engine actuators may be adjusted for cylinder air charge, blow-through, and total cylinder flow. 
         [0044]    As will be appreciated by one of ordinary skill in the art, the method described in  FIG. 3  may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages described herein, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. 
         [0045]    This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, single cylinder, 12, 13, 14, 15, V6, V8, V10, V12 and V16 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.