Method and System for Controlling an Air-Fuel Ratio in an Engine Using a Fuel Source with an Unknown Composition

An engine powered by a gaseous fuel having an unknown composition, comprising:

• at least one cylinder having a combustion chamber disposed therein;
• a piston positioned for displacement within the cylinder;
• an intake port configured to deliver a mixture of air and the gaseous fuel to the cylinder;
• an airflow controller configured to regulate an airflow in the intake port;
• a gaseous fuel flow regulating device configured to regulate a gas mass flow in the intake port;
• an electronic control module (ECM) in electronic communication with the airflow controller and the gaseous fuel flow regulating device, the ECM including
• an assumed gas species input control for allowing an input of an assumed gas species composition for the gaseous fuel,
• a gas species estimation module configured to determine an assumed lower heating value (LHV) for the assumed gas species composition, to determine a perceived lower heating value (LHV) for the gaseous fuel based on a perceived gas mass flow and a gas energy flow for the gaseous fuel, and to update the assumed gas species composition until the assumed LHV and the perceived LHV are aligned, the gas species estimation module providing an aligned gas species composition when the assumed LHV and the perceived LHV are aligned, and
• an airflow estimation module configured to determine a desired air-fuel ratio (AFR) and an airflow necessary to provide the desired AFR using the aligned gas species composition and a desired λ, the airflow estimation module being further configured to send a command to the airflow controller to provide the airflow.

A method for estimating a gas species composition for a gaseous fuel having an unknown composition in an engine powered by the gaseous fuel, comprising:

• receiving an assumed gas species composition;
• determining an assumed lower heating value (LHV) for the assumed gas species composition;
• determining a perceived lower heating value (LHV) for the gaseous fuel based on a perceived gas mass flow and a gas energy flow for the gaseous fuel;
• comparing the assumed LHV and the perceived LHV;
• and
• updating the assumed gas species composition until the assumed LHV and the perceived LHV are aligned, the assumed gas species composition being an approximation of the gas species composition when the assumed LHV and the perceived LHV are aligned.