Various methods and systems are provided for a multi-fuel capable engine. In one example, a system comprises an engine having at least one cylinder controlled via an intake valve, a first fuel system to deliver liquid fuel and a second fuel system to deliver gaseous fuel to the at least one cylinder, a variable valve timing actuation system to adjust one or more of an opening or a closing timing of the intake valve, and a controller. The controller is configured to, during a liquid fuel only mode, adjust the variable valve timing actuation system to close the intake valve at a first timing based at least on engine load, and during a multi-fuel mode, adjust the variable valve timing actuation system to close the intake valve at a second timing.

A method which develops a supercritical combustion chamber environment and combines fumigation and water conversion to superheated steam to effect greater fuel efficiency and reduce exhaust gas pollutants from a compression ignition engine. The invention utilizes the fumigant method by combining two gases (DME and heptane) which autoignite prior to the injection of the liquid water. This pre-combustion of the fumigant gases combined with the engine's compression of the combustion chamber gases is managed to attain a supercritical combustion chamber environment into which the liquid water is injected. This targeted supercritical combustion chamber environment causes the water to become a superheated steam, resulting in significantly greater efficiency and negligible exhaust gas pollutants resulting from the steam engine.

In a multi-fuel system for diesel engines, natural gas is mixed with diesel fuel and conditioned in a mixing chamber before being injected into the mixing chamber of the engine. Filtered blow-by gas may also be introduced into the combustion chamber. A computerized controller is used to determine and control the proportion of diesel fuel, natural gas fuel, the mixing and conditioning of these fuels, and the supply of filtered blow-by gas.

A method for injecting gaseous fuel directly into a combustion chamber of an internal combustion engine in order to heat a catalytic converter, the method including: carrying out a main injection of gaseous fuel directly into the combustion chamber; carrying out a first post-injection following the main injection but prior to an ignition, and following the ignition and preferably following the end of combustion in the combustion chamber, carrying out a second post-injection of gaseous fuel into the combustion chamber.

A fuel system for an internal combustion piston engine includes a first fuel section and a second fuel section in which the first fuel section has a first inlet line connecting respective inlets of the injectors to a tank, and the second fuel section has a second inlet line connecting respective inlets of the injectors to a fuel tank. The second fuel section is arranged to inject the fuel into the combustion chambers for igniting the first fuel, in which first fuel section the inlet line extends from a high pressure pump to the respective injectors, and a fuel return line of the first fuel section extends from each of the injectors to the tank. The fuel return line has a pressure increasing means arranged to the fuel return line of the first fuel section between the injectors and the tank.

A method for operating an engine, comprising port injecting a first quantity of a first gaseous fuel in a cylinder cycle and direct injecting a second quantity of a secondary injectant in the cylinder cycle as a function of a desired air-to-fuel ratio (AFR), the desired AFR based on a temperature of an engine cylinder valve. The desired AFR may be outside the AFR range available during natural gas combustion alone and thus allows for cooler engine operation.

A secondary fuel injection system determines (precisely) a maximum amount of secondary fuel that can be injected into a cylinder during a cycle based upon the rotational speed (RPM) of the engine. A primary fuel injection pulse width of the prior cycle and is used to determine how much heat energy was requested by an engine control module based upon the duration of the injection pulse. Secondary fuel is injected into the intake port of the cylinder after the exhaust valve closes in an amount that is calculated based upon the maximum that can be injected during the allowed calculated time of crankshaft rotation and the amount of heat energy requested in the prior cycle and to include the amount of primary fuel that is then injected into the cylinder is being reduced based upon the amount of heat energy provided by the secondary fuel that was previously injected.

If the pressure in a supply passage drops at a speed greater than a first determination speed in a state in which a first mode for supplying gas fuel to an internal combustion engine is selected, a control apparatus inhibits selection of the first mode. Then, the control apparatus switches from the first mode to a second mode, in energy other than gas fuel is used. In this state, if the pressure in the supply passage drops at a speed greater than a second determination speed, the control apparatus maintains the state in which the second mode is selected. If the pressure in the supply passage drops at a speed lower than the second determination speed, the control apparatus cancels the inhibition of selection of the first mode when it is detected that a manual on-off valve is opened.

Systems, methods and apparatus for controlling operation of dual fuel engines are disclosed that regulate the fuelling amounts provided by a first fuel and a second fuel during operation of the engine. The first fuel can be a liquid fuel and the second fuel can be a gaseous fuel. The fuelling amounts are controlled to improve operational outcomes of the duel fuel engine.

A method of reducing carbonaceous deposits on a fuel injector is provided in which a first fuel composition is supplied to the fuel injector in a dual fuel engine, the first fuel composition comprising natural gas fuel and a first percentage of diesel fuel; and a second fuel composition is supplied to the fuel injector in a dual fuel engine, the second fuel composition comprising a second percentage of diesel fuel that is greater than the first percentage of diesel fuel to cause cavitation to occur within the fuel injector, thereby reducing carbonaceous deposits.