Abstract: A dual fuel injection arrangement for an internal combustion engine. Fuel is injected into the inlet manifold ducts to each engine cylinder via injectors. An arrangement of valves allows selected supply of either a first fuel or a second fuel to the injectors via inlet fuel rail and branch lines. Excess fuel is returned to each supply by way of return line (11). Electronic control units determine injection timing for the selected fuel dependent upon engine parameters for the first fuel and upon an adjusted timing for the second fuel where the adjustment takes account of the different characteristics of the second fuel compared with the first fuel. In particular there is disclosed an arrangement where the first fuel is gasoline and the second fuel is a liquified gas.

Abstract: A method of operating a low boiling point liquid fuel injection system for an internal combustion engine (1) wherein the fuel is stored in a tank (17) and has a variable vapour pressure in the tank (17) dependent upon ambient temperature. The method comprises pumping the fuel to the fuel inlet rail (15) and injectors (8, 9, 10, 11) at an absolute pressure which is maintained at a constant differential above the variable vapour pressure in the tank (17), monitoring the absolute pressure of the fuel and varying the fuel injection pulse width dependent upon the absolute pressure of the fuel together with the other usual engine parameters. The method has particular application where the fuel is a liquified gas.