Various methods and systems are provided for controlling emissions and a likelihood of engine knock during combustion in a multi-fuel engine. A method for an engine includes mixing an amount of a first fuel and an amount of a second fuel to combust a fuel mixture having a fuel ratio of the first fuel relative to the second fuel, the first fuel having a faster combustion flame speed relative to the second fuel, the fuel mixture having an air-to-fuel ratio with an amount of air delivered to the engine. The method further includes controlling either or both of a speed of combustion and a stability of combustion of the fuel mixture with the amount of air delivered to the engine by changing at least one of the fuel ratio, the air-to-fuel ratio, or both of the fuel ratio and the air-to-fuel ratio.

Various methods and systems are provided for a method for a multi-pressure fueling system. In one example, the multi-pressure fueling system includes providing a first fuel delivery pressure enabling high pressure direct injection of a fuel at a first injector and a second fuel delivery pressure insufficient for high pressure direct injection, at a second injector, based on engine operation.

Timing of HHO gas injection into a 4-stroke engine is optimized based on engine operating parameters to improve fuel economy.

Timing of HHO gas injection into a 4-stroke engine is optimized based on engine operating parameters to improve fuel economy.

An engine operable in a premixed combustion system and a diffusion combustion system. The engine includes a main fuel injection valve, a pilot fuel injection valve, a liquid fuel tank, a main fuel supply path, a pilot fuel supply path, a pilot fuel filter, a pilot fuel high-pressure pump, a pilot fuel tank, and a pilot fuel supply pump. The pilot fuel tank stores pilot fuel sent from the pilot fuel high-pressure pump and not injected by the pilot fuel injection valve. This pilot fuel is sent to an automatic backwash filter and a pilot fuel filter while not passing through the liquid fuel tank.

An engine operable in a premixed combustion system and a diffusion combustion system. The engine includes a main fuel injection valve, a pilot fuel injection valve, a liquid fuel tank, a main fuel supply path, a pilot fuel supply path, a pilot fuel filter, a pilot fuel high-pressure pump, a pilot fuel tank, and a pilot fuel supply pump. The pilot fuel tank stores pilot fuel sent from the pilot fuel high-pressure pump and not injected by the pilot fuel injection valve. This pilot fuel is sent to an automatic backwash filter and a pilot fuel filter while not passing through the liquid fuel tank.

Methods and systems for flex fuel engines that have both port fuel injection and direct injection. Operating an engine system includes determining a percent of ethanol in a fuel and determining whether the percent of ethanol is greater than a predetermined threshold. When the percent of ethanol is greater than the predetermined threshold, fuel is supplied only through the direct injection injectors. When the percent of ethanol is not greater than the predetermined threshold, fuel is supplied through a combination of the direct injection injectors and port fuel injection injectors.

An engine including a main fuel injection valve, a pilot fuel injection valve, a liquid fuel supply rail pipe, and a pilot fuel supply rail pipe. The main fuel injection valve supplies liquid fuel from the liquid fuel supply rail pipe to a combustion chamber during combustion in a diffusion combustion system. The pilot fuel injection valve supplies pilot fuel from the pilot fuel supply rail pipe to the combustion chamber in order to ignite gaseous fuel during combustion in a premixed combustion system. The liquid fuel supply rail pipe is disposed at one side of an imaginary vertical plane including an axis of a crank shaft. The pilot fuel supply rail pipe is disposed at the side of the imaginary vertical plane at which the liquid fuel supply rail pipe is disposed.

Spark ignition engine operation at higher RPM so as to reduce alcohol requirements in high efficiency alcohol enhanced gasoline engines is disclosed. Control of engine upspeeding (use of a higher ratio of engine RPM to wheel RPM) so as to achieve an alcohol reduction objective while limiting any decrease in efficiency is described. High RPM alcohol enhanced gasoline engine operation in plug-in series hybrid powertrains for heavy duty trucks and other vehicles is also described.

Spark ignition engine operation at higher RPM so as to reduce alcohol requirements in high efficiency alcohol enhanced gasoline engines is disclosed. Control of engine upspeeding (use of a higher ratio of engine RPM to wheel RPM) so as to achieve an alcohol reduction objective while limiting any decrease in efficiency is described. High RPM alcohol enhanced gasoline engine operation in plug-in series hybrid powertrains for heavy duty trucks and other vehicles is also described.