A method for controlling fuel pressure in an internal combustion engine consuming a gaseous fuel and a liquid fuel comprises steps of determining a gaseous fuel pressure target value as a function of an engine operating condition, pressurizing the liquid fuel to a liquid fuel pressure based on the gaseous fuel pressure target value, and regulating gaseous fuel pressure from the liquid fuel pressure. The gaseous fuel pressure equals the gaseous fuel pressure target value to within a predetermined range of tolerance. A corresponding apparatus controls fuel pressure in a gaseous fuelled internal combustion engine.

A fuel flow detection method of an in-vehicle engine uses gasoline, liquefied gas, and gas as a fuel and adopts a spark ignition system, and a fuel flow is calculated from a detected intake air flow and an air-fuel ratio after combustion or an oxygen ratio.

A gas substitution ratio control system varies natural gas flow to a bi-fuel engine based on detected diesel flow to maintain a desired gas substitution ratio (GSR), without any requirement to sense engine load. In other words, GSR is controlled without monitoring engine load level. In one system, an engine is first calibrated to map actual gas and diesel flows to provide the correct GSR for all engine loads. The calibration data is then stored and diesel flow rate is monitored. The current detected diesel flow rate is used to determine the required gas flow rate for correct GSR. Gas flow to the engine is then adjusted to correspond to the required gas flow rate. Other embodiments meter gas to maintain the diesel flow rate at the same minimum level for all loads, or meter gas and diesel fuel flows to match a map of the limiting fuel energy based GSR (gas fuel energy rate/total fuel energy rate) at all loads for each engine model.

A method for controlling fuel pressure in an internal combustion engine consuming a gaseous fuel and a liquid fuel comprises steps of determining a gaseous fuel pressure target value as a function of an engine operating condition, pressurizing the liquid fuel to a liquid fuel pressure based on the gaseous fuel pressure target value, and regulating gaseous fuel pressure from the liquid fuel pressure. The gaseous fuel pressure equals the gaseous fuel pressure target value to within a predetermined range of tolerance. A corresponding apparatus controls fuel pressure in a gaseous fuelled internal combustion engine.

A method for controlling fuel pressure in an internal combustion engine consuming a gaseous fuel and a liquid fuel comprises steps of determining a gaseous fuel pressure target value as a function of an engine operating condition, pressurizing the liquid fuel to a liquid fuel pressure based on the gaseous fuel pressure target value, and regulating gaseous fuel pressure from the liquid fuel pressure. The gaseous fuel pressure equals the gaseous fuel pressure target value to within a predetermined range of tolerance. A corresponding system controls fuel pressure in a gaseous fuelled internal combustion engine.

Various systems and methods are described for diagnosing injector variability in a dual fuel, multi-injector system. In one example, a single injector in one cylinder is enabled while remaining cylinders are fueled with a first fuel and subsequently, a second fuel is injected via the enabled injector into the one cylinder in a predetermined sequence and fuel rail pressure drops are measured. Further, measured pressure drop after each injection event is corrected for an increase in injector closing delay.

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.

An internal combustion engine system is described herein. The system uses a mixer to mix two fuels to provide for a transition from using only one of the fuels to using only the other fuel as power demand changes. The output of the mixer is provided to the engine as a primary fuel. A controller opens and closes throttle valves to adjust the relative concentrations of a first fuel (e.g., diesel) and a second fuel (e.g., methanol) that enter the mixer. In some examples, rather than removing the desired performance and/or environmental benefits achieved by using the second fuel at power demand levels greater than the maximum achievable by only using the second fuel, the systems described herein allow the use of at least a portion of the second fuel in the primary fuel at those power demand levels.

The invention relates to a bi-fuel system (100) and a method for operating such a system, in which the following steps are performed by a control system (104) being part of the bi-fuel system (100): determining whether a relative amount of first fuel in the second fuel tank (2) is less than a predetermined minimum relative amount of first fuel in the second fuel tank (MIX %_min), and if said relative amount is less than MIX %_min, supplying first fuel via the fuel return line (18) to the second fuel tank (2), by temporarily opening the return line shut-off valve (12).

A bi-fuel control system can include an electronic control module and a control unit that are in communication with each other. The system can include a first set of fuel injectors that are configured to deliver a primary fuel to an engine and can include a second set of fuel injectors that are configured to deliver a secondary fuel to the engine. The bi-fuel control system can operate in either a primary operational state in which the first set of injectors is used or a secondary operational state in which the second set of injectors is used. In either operational state, the electronic control module can control the respective set of injectors independently from the control unit.