Patent Publication Number: US-2010126481-A1

Title: Engine control system having emissions-based adjustment

Description:
STATEMENT OF GOVERNMENT INTEREST  
     This invention was made with Government support under Contract No. DE-FC02-01CH11079, awarded by the Department of Energy. The Government may have certain rights in this invention. 
    
    
     TECHNICAL FIELD 
     The present disclosure is directed to an engine control system and, more particularly, to an engine control system having emissions-based adjustment. 
     BACKGROUND  
     Combustion engines are often used for power generation applications. These engines can be gaseous-fuel driven and implement lean burn, during which air/fuel ratios are higher than in conventional engines. For example, these gas engines can admit about 75% more air than is theoretically needed for stoichiometric combustion. Lean-burn engines increase fuel efficiency because they utilize homogeneous mixing to burn less fuel than a conventional engine and produce the same power output. 
     Lean-burn engines typically produce and emit less NOx than conventional combustion engines. In light of increasing government standards for reducing NOx emissions, the ability of lean-burn engines to produce less NOx may provide a significant benefit. However, a shortcoming associated with gaseous-fuel driven engines relates to measuring NOx emissions for purposes of control. Conventional methods for detecting NOx emissions typically require additional components and/or sensors disposed in an exhaust system, which may be inefficient and/or costly. 
     An exemplary virtual NOx sensor is described in U.S. Pat. No. 6,882,929 B2 (the &#39;929 patent), issued to Liang et al. on Apr. 19, 2005. The &#39;929 patent discloses a process for controlling NOx emissions of a target engine that includes predicting NOx values based on a model reflecting a predetermined relationship between control parameters and NOx emissions. The system of the &#39;929 patent monitors control parameters such as intake manifold temperature and intake manifold pressure. The system inputs the control parameters into the model, which may include a neural network. The model then calculates an estimated NOx emission and provides the data as an output. The system of the &#39;929 patent then adjusts one or more operating parameters of the engine based on the estimated NOx data. 
     Although the system of the &#39;929 patent may provide ways to calculate and control NOx emissions, the system may be inaccurate. Specifically, the system of the &#39;929 patent utilizes control parameters from outside of the engine&#39;s combustion chambers (e.g., intake manifold temperature and pressure), which may not accurately represent the combustion process occurring within the combustion chamber. 
     The present disclosure is directed to overcoming one or more of the shortcomings set forth above and/or other deficiencies in existing technology. 
     SUMMARY OF THE DISCLOSURE  
     In accordance with one aspect, the present disclosure is directed toward a control system for an engine having a first cylinder and a second cylinder. The control system includes an air/fuel ratio control device configured to affect an air/fuel ratio within the first and second cylinders. The control system also includes a first sensor configured to generate a first signal indicative of a combustion pressure within the first cylinder, and a second sensor configured to generate a second signal indicative of a combustion pressure within the second cylinder. The control system further includes a controller in communication with the air/fuel ratio control device and the first and second sensors. The controller is configured to determine a NOx production within the first cylinder based on the first signal, and to determine a NOx production within the second cylinder based on the second signal. The controller is also configured to calculate a total NOx production of the engine based on at least the NOx produced within the first and second cylinders, and to selectively regulate the air/fuel ratio control device to adjust the air/fuel ratio within the first and second cylinders based on the total NOx production of the engine. 
     According to another aspect, the present disclosure is directed toward a method of operating an engine. The method includes sensing a parameter indicative of a first combustion pressure within a first cylinder of the engine, and determining a NOx production within the first cylinder based on the first combustion pressure. The method also includes sensing a parameter indicative of a second combustion pressure within a second cylinder of the engine, and determining a NOx production within the second cylinder based on the second combustion pressure. The method further includes calculating a total NOx production of the engine based on at least the NOx produced within the first cylinder and the NOx produced within the second cylinder, and selectively adjusting an air/fuel ratio within the first and second cylinders based on the total NOx production. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic illustration of an exemplary disclosed power system. 
     
    
    
     DETAILED DESCRIPTION  
     An exemplary disclosed power system  10  is disclosed in  FIG. 1 . Power system  10  may include an engine  105 , an intake system  115 , an exhaust system  120 , and a control system  125 . Intake system  115  may deliver air and/or fuel to engine  105 , while exhaust system  120  may direct combustion gases from engine  105  to the atmosphere. Control system  125  may control an operation of intake system  115  and/or exhaust system  120 . 
     Engine  105  may be a four-stroke diesel, gasoline, or gaseous fuel-powered engine. As such, engine  105  may include an engine block  130  at least partially defining a plurality of cylinders  135 . It is contemplated that engine  105  may include any number of cylinders  135  and that cylinders  135  may be disposed in an “in-line” configuration, a “V” configuration, or in any other suitable configuration. 
     A piston  140  may be slidably disposed within each cylinder  135 , so as to reciprocate between a top-dead-center (TDC) position and a bottom-dead-center (BDC) position during an intake stroke, a compression stroke, a combustion or power stroke, and an exhaust stroke. Pistons  140  may be operatively connected to a crankshaft  145  via a plurality of connecting rods  150 . Crankshaft  145  may be rotatably disposed within engine block  130 , and connecting rods  150  may connect each piston  140  to crankshaft  145  so that a reciprocating motion of each piston  140  results in a rotation of crankshaft  145 . Similarly, a rotation of crankshaft  145  may result in a sliding motion of each piston  140  between the TDC and BDC positions. 
     One or more cylinder heads  155  may be connected to engine block  130  to form a plurality of combustion chambers  160 . As shown in  FIG. 1 , cylinder head  155  may include a plurality of intake passages  162  and exhaust passages  163  integrally formed therein. One or more intake valves  165  may be associated with each cylinder  135  and movable to selectively block flow between intake passages  162  and combustion chambers  160 . One or more exhaust valves  170  may also be associated with each cylinder  135  and movable to selectively block flow between combustion chambers  160  and exhaust passages  163 . Additional engine components may be disposed in cylinder head  155  such as, for example, a plurality of spark plugs  172  that ignite an air/fuel mixture in combustion chambers  160 . 
     Engine  105  may include a plurality of valve actuation assemblies  175  that affect movement of intake valves  165  and/or exhaust valves  170 . Each cylinder  135  may have an associated valve actuation assembly  175 . Each valve actuation assembly  175  may include a rocker arm  180  connected to move a pair of intake valves  165  and/or a pair of exhaust valves  170  via a bridge  182 . Rocker arm  180  may be mounted to cylinder head  155  at a pivot point  185 , and connected to a rotating camshaft  200  by way of a push rod  190 . Camshaft  200  may be operatively driven by crankshaft  145  to cyclically open and close intake valves  165  and exhaust valves  170 , and may include a plurality of cams  195  that engage and move push rods  190 . 
     Intake system  115  may direct air and/or fuel into combustion chambers  160 , and may include a single fuel injector  210 , a compressor  215 , an intake manifold  220 , and a throttle valve  232 . Compressor  215  may compress and deliver a mixture of air and fuel from fuel injector  210  to intake manifold  220 . Throttle valve  232  may vary an amount of air delivered to intake manifold  220  and fuel injector  210  may vary an amount of fuel delivered to intake manifold  220 . 
     Compressor  215  may draw ambient air into intake system  115  via a conduit  225 , compress the air, and deliver the compressed air to intake manifold  220  via a conduit  230 . In some embodiments, fuel injector  210  may inject fuel into the air flow prior to compression such that the air/fuel mixture is compressed by compressor  215 . This delivery of compressed air or air/fuel mixture may help to overcome a natural limitation of combustion engines by eliminating an area of low pressure within cylinders  135  created by a downward stroke of pistons  140 . Therefore, compressor  215  may increase the volumetric efficiency within cylinders  135 , allowing more air/fuel mixture to be burned, resulting in a larger power output from engine  105 . It is contemplated that a cooler for further increasing the density of the air/fuel mixture may be associated with compressor  215 , if desired. 
     Fuel injector  210  may be an air/fuel ratio control device for injecting fuel at a low pressure into conduit  225 , upstream of compressor  215 , to form an air/fuel mixture. Fuel injector  210  may be selectively modulated by control system  125  to inject an amount of fuel into intake system  115  to substantially achieve a desired air/fuel ratio of the air/fuel mixture. When the amount of fuel injected by fuel injector  210  increases, while the amount of air flow remains constant, the air/fuel ratio may decrease. When the amount of fuel injected by fuel injector  210  decreases, while the amount of air flow remains constant, the air/fuel ratio may increase. Air/fuel ratios appropriate for lean burn engines may be, for example, between about 20:1 to about 65:1. 
     Throttle valve  232  may also be an air/fuel ratio control device for controlling an amount of air flow through conduit  225 . Throttle valve  232  may be any suitable valve for varying air flow such as, for example, a butterfly valve or other variable restriction valve. Throttle valve  232  may be located upstream of compressor  215  and selectively modulated by control system  125  to vary air flow into intake system  115  to substantially achieve the desired air/fuel ratio of the air/fuel mixture. When the air flow through intake system  115  is increased via throttle valve  232 , while the amount of fuel injected remains constant, the air/fuel ratio may increase. When the air flow through intake system  115  is decreased via throttle valve  232 , while the amount of fuel injected remains constant, the air/fuel ratio may decrease. 
     Exhaust system  120  may direct exhaust gases from engine  105  to the atmosphere. Exhaust system  120  may include a turbine  235  connected to exhaust passages  163  of cylinder head  155  via a conduit  245 . Exhaust gas flowing through turbine  235  may cause turbine  235  to rotate. Turbine  235  may then transfer this mechanical energy to drive compressor  215 , where compressor  215  and turbine  235  form a turbocharger  250 . In one embodiment, turbine  235  may include a variable geometry arrangement  255  such as, for example, variable position vanes or a movable nozzle ring. Variable geometry arrangement  255  may also be considered an air/fuel ratio control device and may be adjusted to affect the pressure of air/fuel mixture delivered by compressor  215  to intake manifold  220 . In embodiments where fuel injector  210  is located downstream of compressor  215 , an increase in the pressure of air affected via variable geometry arrangement  255  may cause more air to be delivered to cylinders  135 , resulting in an increase of the air/fuel ratio. In contrast, a decrease in the pressure of air affected via variable geometry arrangement  255  may cause less air to be delivered to cylinders  135 , resulting in a decrease of the air/fuel ratio. Turbine  235  may be connected to an exhaust outlet via a conduit  260 . It is also contemplated that turbocharger  250  may be replaced by any other suitable forced induction system known in the art such as, for example, a supercharger, if desired. 
     The air/fuel ratio of the air/fuel mixture that is delivered to cylinders  135  may affect the amount of NOx produced by engine  105 . As the air/fuel ratio increases (i.e., becomes leaner), a combustion flame within combustion chamber  160  may become well-distributed, causing the air/fuel mixture to burn at a lower temperature. This lower temperature may slow the chemical reaction of the combustion process, thereby decreasing NOx production. Therefore, as the air/fuel ratio increases, NOx production may decrease. In contrast, as the air/fuel ratio decreases, the amount of NOx produced by engine  105  may increase (i.e., as combustion becomes less lean, NOx production may increase). 
     Control system  125  may include a controller  270  configured to modulate the air/fuel ratio control devices of power system  10  in response to input from one or more sensors  272 . Sensors  272  may be configured to monitor an engine parameter indicative of NOx production within cylinders  135 . In one example, the engine parameter may be a combustion pressure within cylinders  135 . Each sensor  272  may be disposed within an associated cylinder  135  (i.e., in fluid contact with a respective one of combustion chambers  160 ), and may be electrically connected to controller  270 . Sensor  272  may be any suitable sensing device for sensing an in-cylinder pressure such as, for example, a piezoelectric crystal sensor or a piezoresistive pressure sensor. Sensors  272  may measure a pressure within cylinders  135  during, for example, the compression stroke and/or the power stroke, and may generate a corresponding signal. Sensors  272  may transfer signals that are indicative of the pressures within cylinders  135  to controller  270 . Based on these signals, controller  270  may determine NOx production for each cylinder  135  and, subsequently, a total NOx production of engine  105 . Based on the total NOx production, controller  270  may then control the air/fuel ratio control devices such that NOx production is at a desired amount. 
     Controller  270  may be any type of programmable logic controller known in the art for automating machine processes, such as a switch, a process logic controller, or a digital circuit. Controller  270  may serve to control the various components of power system  10 . Controller  270  may be electrically connected to the plurality of sensors  272  via a plurality of electrical lines  280 . Controller  270  may also be electrically connected to variable geometry arrangement  255  via an electrical line  285  and to an actuator of throttle valve  232  via an electrical line  290 . It is also contemplated that controller  270  may be electrically connected to additional components and sensors of power system  10  such as, for example, an actuator of fuel injector  210 , if desired. 
     Controller  270  may include input arrangements that allow it to monitor signals from the various components of power system  10  such as sensors  272 . Controller  270  may rely upon digital or analog processing of input received from components of power system  10  such as, for example, sensors  272  and an operator interface. Controller  270  may utilize the input to create output for controlling power system  10 . Controller  270  may include output arrangements that allow it to send output commands to the various components of power system  10  such as variable geometry arrangement  255 , fuel injector  210 , throttle valve  232  and/or an operator interface that includes a signaling device to alert the operator of an engine status. 
     Controller  270  may have stored in memory one or more engine maps and/or algorithms. Controller  270  may reference these maps to determine a required change in operation of the air/fuel ratio control devices required to affect the desired NOx production and emission and/or a capacity of the air/fuel ratio control devices for the modification. Each of these maps may include a collection of data in the form of tables, graphs, and/or equations. 
     Controller  270  may have stored in memory algorithms associated with determining required changes in operation of the air/fuel ratio control devices based on engine parameters such as, for example, combustion pressure. For example, controller  270  may include an algorithm that performs a statistical analysis of the combustion pressures within the plurality of cylinders  135  from combustion cycle to combustion cycle. Based on input received from sensors  272 , the algorithm may determine, for example, an average NOx production per combustion cycle for each cylinder  135  and/or for all of cylinders  135 . The algorithm may also determine the statistical deviation of the NOx production of each cylinder  135  from the average NOx production of all of cylinders  135 . 
     In one example, controller  270  may have a stored algorithm for determining a heat release profile of each cylinder  135  based on the measured cylinder pressures. Controller  270  may then use the heat release values in the algorithm to determine a temperature level in combustion chamber  160  over time (i.e., a time temperature history). Controller  270  may use the time temperature histories of the plurality of cylinders  135  in the algorithm to determine an estimate of total NOx production from cylinders  135 . 
     Based on the determined estimate of total NOx production, controller  270  may determine a desired air/fuel ratio for engine  105 . Controller  270  may have stored in memory one or more engine maps identifying desired NOx production levels that may correspond, for example, to emissions standards. Controller  270  may have stored in memory one or more engine maps that relate varying levels of total NOx production to corresponding air/fuel ratios of the air/fuel mixture delivered to cylinders  135 . Based on these engine maps, controller  270  may identify when a determined estimate of total NOx production exceeds a desired amount of NOx production, and then select a desired air/fuel ratio that corresponds to the desired NOx production. Controller  270  may control the air/fuel control devices to adjust the air/fuel ratio to the desired air/fuel ratio, thereby adjusting the NOx production toward the desired NOx production. 
     In another example, controller  270  may also have a stored algorithm for determining an operational status of an engine component based on input from sensors  272  such as, for example, based on the average combustion pressure, the heat release history, and/or the NOx production. Controller  270  may use the signals from sensors  272  as input to an algorithm that compares the parameters of a given cylinder  135  to expected parameters for that cylinder  135  at various times during the combustion cycle. Based on the comparison, controller  270  may identify, for example, a parameter difference that is indicative of a leak of mass from cylinder  135  or poor/improper combustion. For example, the difference in the parameter may be caused by a leaking intake valve  165  and/or exhaust valve  170 , a broken piston ring, or a non-functioning spark plug  172 , such that combustion does not occur or is poor. 
     In another example, controller  270  may have a stored algorithm for determining an operational status of an engine component based on a statistical deviation of the parameter in one cylinder  135  from an average parameter for all of cylinders  135 . Controller  270  may use the signals from sensors  272  as input to an algorithm that compares the measured parameter of each cylinder  135  to the measured or historical parameters of the remainder of cylinders  135 . Controller  270  may calculate an average parameter for the plurality of cylinders  135  and compare the measured parameter of each cylinder  135  to that average parameter. Additionally, controller  270  may compare the measured parameter of each cylinder  135  to a calculated theoretical average parameter for all of cylinders  135 . Controller  270  may determine a statistical deviation of the parameter of each cylinder  135  from the average parameter to identify a cylinder  135  having a malfunctioning component. For example, sensor  272  may indicate to controller  270  that a given cylinder  135  has a parameter that significantly deviates from the average parameter, indicating a malfunction. 
     Based on output from one or more algorithms indicative of NOx production and/or operational status, controller  270  may vary an air/fuel ratio of the air/fuel mixture that is delivered to cylinders  135 . Controller  270  may control fuel injector  210 , throttle valve  232 , variable geometry arrangement  255  of turbine  235 , and/or other components to achieve the desired air/fuel ratio based on the algorithm output. 
     INDUSTRIAL APPLICABILITY 
     The disclosed engine control system may be used in any machine having a combustion engine where control of NOx production is required. For example, the engine control system may be particularly applicable to gaseous-fuel driven engines that implement lean burn. Operation of power system  10  will now be described. 
     Sensors  272  may measure a combustion pressure within cylinders  135  and provide the pressure measurements as signals to controller  270 . Controller  270  may use signals as input to one or more stored algorithms for determining a total production of NOx from cylinders  135 . Based on the NOx production of each cylinder  135  and/or a total NOx production of engine  105 , controller  270  may adjust the air/fuel ratio of the mixture provided to each cylinder  135 . For example, controller  270  may adjust an amount of fuel injected by fuel injector  210  and/or an amount of air allowed into intake manifold  220  by throttle valve  232  based on the determined NOx production. Controller  270  may also vary a geometry of turbocharger  250  based on the NOx production. 
     For example, sensors  272  may provide signals indicative of a combustion pressure that is lower than desired to controller  270 . Using the signals from sensors  272 , controller  270  may use one or more stored algorithms to determine that a NOx production of engine  105  is correspondingly greater than desired. Controller  270  may control the air/fuel ratio control devices to increase the air/fuel ratio of the air/fuel mixture entering cylinders  135 , thereby decreasing NOx emissions toward a desired level. For example, fuel injector  210  may inject less fuel, throttle valve  232  may increase air flow, and/or turbocharger  250  may increase the pressure of air delivered to cylinders  135 . In contrast, sensors  272  may provide signals indicative of a combustion pressure that is higher than desired to controller  270 . Using the signals from sensors  272 , controller  270  may use one or more stored algorithms to determine that a NOx production of engine  105  is correspondingly lower than required. Controller  270  may control the air/fuel ratio control devices to decrease the air/fuel ratio of the air/fuel mixture entering cylinders  135 , thereby increasing NOx emissions toward a desired level. For example, fuel injector  210  may inject more fuel, throttle valve  232  may decrease air flow, and/or turbocharger  250  may decrease the pressure of air delivered to cylinders  135 . 
     Controller  270  may also use the signals provided from sensors  272  as input to one or more stored algorithms for determining an operational status of an engine component. Based on the operational status output of the algorithms, controller  270  may determine that one or more intake valves  165 , exhaust valves  170 , spark plugs  172 , or piston rings may be malfunctioning. Based on the operational status, controller  270  may, for example, adjust power system  10  to signal the condition to an operator and/or adjust the air/fuel ratio of the air/fuel mixture. Controller  270  may adjust fuel injector  210  or throttle valve  232  of power system  10  to adjust the air/fuel ratio based on the operational status. Controller  270  may also vary a geometry of turbocharger  250  based on the operational status. 
     For example, sensors  272  may provide signals indicative of a combustion pressure that is lower than desired to controller  270 . Using the signals from sensors  272 , controller  270  may use one or more stored algorithms to determine that one or more intake valves  165 , exhaust valves  170 , and/or piston rings are leaking, and thereby lowering combustion pressure. Additionally, when a component is leaking, the power produced by engine  105  may be less than desired. Controller  270  may also determine that a NOx production is higher than desired. Controller  270  may signal the operation status to the operator interface and/or control the air/fuel ratio control devices to increase the air/fuel ratio of the air/fuel mixture entering cylinders  135 , thereby decreasing NOx emissions toward a desired level. 
     In another example, sensors  272  may provide signals indicative of a combustion pressure that is higher than desired to controller  270 . Using the signals from sensors  272 , controller  270  may use one or more stored algorithms to determine that one or more intake valves  165  and/or exhaust valves  170  are operating improperly (e.g., valve timing is improper), and/or one or more spark plugs  172  are firing at an improper timing, thereby increasing combustion pressure. Controller  270  may also determine that a NOx production is lower than desired. Controller  270  may signal the operation status to the operator interface and/or control the air/fuel ratio control devices to decrease the air/fuel ratio of the air/fuel mixture entering cylinders  135 , thereby increasing NOx emissions toward a desired level. 
     Because in-cylinder measurements may be reliable indicators of NOx emissions, controller  270  may accurately estimate NOx production. Controller  270  may also use this accurate NOx estimate to adjust the operation of power system  10  such that NOx emissions are maintained at a desired level. Controller  270  may also use in-cylinder measurements to determine an operational status of components of power system  10 , thereby providing an efficient diagnostic tool for extending a service life of power system  10 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed apparatus and method. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed method and apparatus. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.