Fuel limiter for a uniflow-scavenged, two-stroke cycle, opposed-piston engine

Abstract

Control of fuel flow in a uniflow-scavenged, two-stroke cycle, opposed-piston engine includes limiting an amount of torque or fuel in response to a torque demand, based upon a comparison and a selection of fuel delivery options derived from a global airflow parameter and/or a trapped airflow parameter.

1 . A method of operating a uniflow-scavenged, two-stroke cycle, opposed-piston engine with a fuel source, comprising:
 operating the engine according to a mode of control;   providing charge air to cylinders of the engine;   receiving a torque demand for a desired torque level of the engine;   determining a minimum value of an air to fuel ratio (AFR) of the engine based on engine speed and the desired torque level;   determining a value of mass airflow through the engine based on air flow conditions of the engine;   determining a maximum diesel fuel quantity limit based on the minimum value of AFR and the value of mass airflow through the engine;   limiting a quantity of diesel fuel provided to the engine based the lesser of a maximum allowable torque derived from the maximum fuel quantity limit and the desired torque level; and,   when the engine is operated according to a fuel mode of control, providing a limited fuel command indicative of the limited quantity of diesel fuel to the fuel source; and,   when the engine is operated according to a torque mode of control, providing a limited torque command indicative of the limited quantity of diesel fuel to the fuel source.   
     
     
         2 . The method of  claim 1 , wherein the value of mass airflow is based on one of: a mass of charge air provided to a cylinder of the engine during a cycle of engine operation; and, a mass of charge air trapped in the cylinder by a last port of the cylinder to close during a cycle of engine operation. 
     
     
         3 . The method of  claim 2 , wherein the minimum value of AFR is a smoke-limited AFR. 
     
     
         4 . The method of  claim 2 , wherein the value of a mass of charge air provided to a cylinder of the engine during a cycle of engine operation is determined by measurement using one of a mass airflow sensor and a NOx/0 2  sensor. 
     
     
         5 . The method of  claim 2 , wherein the value of a mass of charge air trapped in a cylinder by the last port of the cylinder to close during one cycle of engine operation is determined by measurement using a virtual sensor. 
     
     
         6 . The method of  claim 1 , wherein the AFR is one of: a global AFR that is determined with reference to the total mass of charge air delivered to a cylinder during one cycle of engine operation; and, a trapped AFR that is determined with reference to the total mass of charge air trapped in a cylinder by the last port of the cylinder to close during one cycle of engine operation. 
     
     
         7 . The method of  claim 6 , wherein the minimum value of AFR is a smoke-limited AFR. 
     
     
         8 . The method of  claim 6 , wherein the total mass of charge air provided to a cylinder of the engine during a cycle of engine operation is determined by measurement using one of a mass airflow sensor and a NOx/0 2  sensor. 
     
     
         9 . The method of  claim 6 , wherein the total mass of charge air trapped in a cylinder by the last port of the cylinder to close during one cycle of engine operation is determined by measurement using a virtual sensor. 
     
     
         10 . A method for limiting emission of smoke by a uniflow-scavenged, two-stroke cycle, opposed-piston engine with a diesel fuel source during transient demands for increased torque, comprising:
 receiving a torque demand for a desired torque level during a transient operation of the engine;   obtaining a minimum value of a smoke-limited AFR (air to fuel ratio) of the engine from a smoke map based on engine speed and the desired torque level;   determining a measured value of a mass airflow of the engine;   determining a maximum diesel fuel quantity limit based on the minimum value of the smoke-limited AFR and the measured value of mass airflow of the engine;   limiting a quantity of diesel fuel provided to the engine based on the lesser of a maximum allowable torque derived from the maximum diesel fuel quantity limit and the desired torque level; and,   providing a limited torque command indicative of the limited quantity of fuel to the fuel source.   
     
     
         11 . The method of  claim 10 , wherein the smoke-limited AFR is based on one of: a mass of charge air provided to a cylinder of the engine during a cycle of engine operation; and, a mass of charge air trapped in the cylinder by a last port of the cylinder to close during a cycle of engine operation. 
     
     
         12 . The method of  claim 10 , wherein the measured value of mass airflow is based on one of: a mass of charge air provided to a cylinder of the engine during a cycle of engine operation; and, a mass of charge air trapped in the cylinder by a last port of the cylinder to close during a cycle of engine operation. 
     
     
         13 . The method of  claim 12 , wherein the value of a mass of charge air provided to a cylinder of the engine during a cycle of engine operation is determined by measurement using one of a mass airflow sensor and a NOx/02 sensor. 
     
     
         14 . The method of  claim 12 , wherein the value of a mass of charge air trapped in a cylinder by the last port of the cylinder to close during one cycle of engine operation is determined by measurement using a virtual sensor. 
     
     
         15 . The method of  claim 10 , wherein the AFR is one of: a global AFR that is determined with reference to the total mass of charge air delivered to a cylinder during one cycle of engine operation; and, a trapped AFR that is determined with reference to the total mass of charge air trapped in a cylinder by the last port of the cylinder to close during one cycle of engine operation. 
     
     
         16 . A uniflow-scavenged, two-stroke cycle, opposed-piston engine, comprising:
 at least one cylinder, two pistons disposed crown-to-crown in a bore of the at least one cylinder for reciprocating movement in opposing directions, and an inlet port and an exhaust port near respective ends of the at least one cylinder;   an air handling system for transporting charge air to the inlet port and exhaust from the exhaust port:   a diesel fuel handling system for providing diesel fuel to the at least one cylinder to be mixed with charge air therein and ignited by heat of charge air compressed by the two pistons; and,   a smoke limiter means for:   accepting a desired load signal from a sensor of the engine;   responsively to the desired load signal, determining a quantity of diesel fuel that can be provided to the at least one cylinder without exceeding a smoke-limited air/fuel ratio that limits a production of smoke by the opposed-piston engine in response to a rich mixture of charge air and diesel fuel; and,   providing a command to the diesel fuel handling system indicative of the quantity of diesel fuel.   
     
     
         17 . The uniflow-scavenged, two-stroke cycle, opposed-piston engine of  claim 16  further comprising an exhaust gas recirculation (EGR) loop. 
     
     
         18 . The uniflow-scavenged, two-stroke cycle, opposed-piston engine of  claim 16 , in which the diesel fuel handling system comprises a common rail fuel handling system for delivering diesel fuel to the at least one cylinder by direct injection into the at least one cylinder. 
     
     
         19 . The uniflow-scavenged, two-stroke cycle, opposed-piston engine of  claim 18 , in which the common rail fuel handling system comprises multiple fuel injectors mounted for direct injection into space in the at least one cylinder between top dead center locations of end surfaces of the two pistons. 
     
     
         20 . The uniflow-scavenged, two-stroke cycle, opposed-piston engine of  claim 18 , in which the common rail fuel handling system includes two fuel injectors, at least one rail/accumulator mechanism, and a fuel pump.