Method and apparatus for adaptive feedback control of an excess air ratio in a compression ignition natural gas engine

A compression ignition internal combustion engine, comprising

• a plurality of cylinders;
• a gaseous fuel supply system associated with the cylinders;
• a liquid fuel supply system associated with the cylinders;
• an intake manifold cooperating with each of the cylinders;
• an exhaust manifold also cooperating with each of the cylinders;
• an exhaust gas oxygen sensor that cooperates with the exhaust manifold and that measures exhaust gas oxygen concentration in the exhaust generated by the cylinders;
• and
• a control system that
• controls operation of the gaseous fuel supply based at least in part on gas excess air fuel ratio;
• predicts a gas excess air ratio for the engine based at least in part on at least one detected current operating parameter;
• calculates a predicted exhaust gas oxygen concentration for exhaust gas generated by the engine based on the predicted gas excess air ratio;
• using at least one time-based factor, filters a plurality of the measured exhaust oxygen concentration measurements and a plurality of the predicted exhaust oxygen concentrations to obtain a filtered measured exhaust gas concentration value and a filtered predicted exhaust oxygen concentration value,
• compares the filtered exhaust gas oxygen concentration to the filtered predicted exhaust gas oxygen concentration value to determine an exhaust gas oxygen concentration deviation value, and, if the deviation value exceeds a designated threshold,
• calculates a corrected gas excess air ratio.

A computer-implemented method, comprising:

• using at least one programmed computer, predicting an exhaust gas oxygen concentration for exhaust gas generated by a gaseous fueled compression ignition engine;
• using the at least one programmed computer, measuring an actual exhaust gas oxygen concentration for the engine;
• using the at least one programmed computer, using at least one time-based factor, filtering a plurality of the measured exhaust oxygen concentration measurements and a plurality of the predicted exhaust oxygen concentrations to obtain a filtered measured exhaust gas concentration value and a filtered predicted exhaust oxygen concentration value;
• and
• using the at least one programmed computer, calculating a corrected predicted gas excess air ratio and a corrected measured gas excess air ratio using the filtered predicted and measured exhaust gas oxygen concentration values.