Method and system for estimating the specific gravity of an unknown fuel source in a multi-fuel engine

An engine powered by a gaseous fuel having an unknown specific gravity, 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;
• a gas valve configured to regulate a gas mass flow into the intake port;
• a gas rail configured to supply the gas valve with the gaseous fuel, the gas valve being configured to generate a pressure wave in the gas rail when the gas valve is opened and closed;
• a pressure sensor in the gas rail configured to detect the pressure wave;
• and
• a specific gravity estimation module configured to determine a frequency of the pressure wave detected by the pressure sensor, and to estimate the specific gravity of the gaseous fuel based on the frequency of the pressure wave.

A method for estimating a specific gravity of a gaseous fuel, the gaseous fuel powering a dual fuel engine configured to run on at least the gaseous fuel and diesel fuel, the engine including a plurality of cylinders, an intake port associated with each one of the cylinders, a gas valve associated with each one of the intake ports and configured to supply the intake port with the gaseous fuel, a gas rail configured to supply the gas valves with the gaseous fuel, and a microprocessor adapted to perform the method, said method comprising:

• running one of the cylinders in gas mode in which the cylinder is supplied with the gaseous fuel as a primary fuel source;
• running the remaining cylinders in diesel mode in which the diesel fuel is used as a sole fuel source;
• establishing a pressure wave in the gas rail by opening and closing the gas valve associated with the cylinder running in gas mode, the pressure wave traveling at a speed of sound in the gaseous fuel;
• determining a frequency of the pressure wave in the gas rail;
• and
• estimating the specific gravity of the gaseous fuel based on the frequency of the pressure wave.