A method of controlling fuel injection in a dual fuel engine system includes determining, with a first controller, a diesel injection pulse indicative of a first amount of diesel fuel to be injected into a combustion chamber of the engine and a first timing at which the first amount of diesel fuel is to be injected. The method also includes determining, with a second controller, a combined injection pulse based on the diesel injection pulse. The method further includes injecting the second amount of diesel fuel and the third amount of natural gas into the combustion chamber in accordance with the combined injection pulse. In such a method, injection in accordance with the combined injection pulse results in a combustion event characterized by a second combustion characteristic substantially equal to a first combustion characteristic associated with the diesel injection pulse.

A method of controlling fuel injection in a dual fuel engine system includes determining, with a first controller, a diesel injection pulse indicative of a first amount of diesel fuel to be injected into a combustion chamber of the engine and a first timing at which the first amount of diesel fuel is to be injected. The method also includes determining, with a second controller, a combined injection pulse based on the diesel injection pulse. The method further includes injecting the second amount of diesel fuel and the third amount of natural gas into the combustion chamber in accordance with the combined injection pulse. In such a method, injection in accordance with the combined injection pulse results in a combustion event characterized by a second combustion characteristic substantially equal to a first combustion characteristic associated with the diesel injection pulse.

A method for estimating a specific gravity of a gaseous fuel is described. The gaseous fuel may power an engine and the engine may include a cylinder, a gas valve configured to supply an intake port of the cylinder with the gaseous fuel, a gas rail configured to deliver the gaseous fuel to the gas valve, and a microprocessor adapted to perform the method. The method may comprise establishing a pressure wave in the gas rail by opening and closing the gas valve, wherein the pressure wave travels at the speed of sound in the gaseous fuel. The method may further comprise 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.