An ignition timing controller includes a storage and a processor configured or programmed to function as an ignition timing control section and a knocking determining section. The storage stores at least one of a first ignition timing map associated with a first fuel or a second ignition timing map associated with a second fuel more likely to cause knocking of an internal combustion engine than the first fuel. The ignition timing control section controls the ignition timing based on the first ignition timing map by executing a timing retardation based on the first ignition timing map when it is determined that knocking of the internal combustion engine has occurred. The ignition timing control section controls the ignition timing of the internal combustion engine based on the second ignition timing map by executing a timing advancement correction based on the second ignition timing map when it is determined that the knocking of the internal combustion engine has not occurred.

Premixed engines including dual fuel engines can experience abnormal combustion characteristics including misfire, pre-ignition and knock. A method for detecting and mitigating abnormal combustion in an engine comprises sensing frequency components of an acoustic signal associated with a combustion chamber during a combustion cycle, the frequency components representative of at least one of a normal and an abnormal combustion characteristic; determining an in-cylinder pressure signal as a function of the acoustic signal; calculating as functions of the in-cylinder pressure signal at least one of a knock index, a gross indicated mean effective pressure and a start of combustion timing; detecting the abnormal combustion characteristic is at least one of (a) a misfire event when the gross indicated mean effective pressure is less than a predetermined mean effective pressure value; (b) a pre-ignition event when the start of combustion timing is advanced of a start of ignition timing; and (c) an engine knock event when the knock index is greater than a predetermined knock value; and performing a mitigation strategy for the detected abnormal combustion characteristic.

A method of estimating antiknock properties of a multi-fuel injection internal combustion engine includes: acquiring a first antiknock property-correlated parameter value while only a first fuel having a low octane rating is injected in a first load range; estimating a first antiknock property of the first fuel based on the first antiknock property-correlated parameter value; acquiring a second antiknock property-correlated parameter value while the first fuel and a second fuel which has a high octane rating higher than the low octane rating are injected in a second load range higher than the first load range; and estimating a second antiknock property of the second fuel based on the second antiknock property-correlated parameter value and the first antiknock property of the first fuel.

According to one or more embodiments, an internal combustion engine may be operated by a method which includes one or more of injecting a first fuel and a second fuel into an engine cylinder to form a fuel mixture, and combusting the fuel mixture with a spark plug to translate a piston housed in the engine cylinder and rotate a crank shaft coupled to the piston. The first fuel may comprise a greater octane rating than the second fuel. A target CA50 may correspond to a minimum in specific fuel consumption of the fuel mixture. The spark plug may initiate combustion at a time such that the internal combustion engine operates with an operational CA50 that is within 20 degrees of the target CA50.

Methods and systems are provided for improving fuel usage while addressing knock by adjusting the use of spark retard and direct injection of a knock control fluid based on engine operating conditions and the composition of the injected fluid. One or more engine parameters, such as EGR, VCT, boost, throttle position, and CMCV, are coordinated with the direct injection to reduce torque and EGR transients.

Methods and systems are provided for controlling fueling and mitigating knock in internal combustion engines, such as multi-fuel engines. In one example, a method may include monitoring a frequency of knock events corresponding to one or more engine cylinders, and dynamically increasing a substitution ratio while the frequency of knock events is less than a maximum action threshold. In some examples, the method may further include actively adjusting one or more engine operating conditions to decrease the substitution ratio responsive to a severity of knocking in the one or more engine cylinders being greater than or equal to a threshold severity.

Methods and systems are provided for improving fuel usage while addressing knock by adjusting the use of spark retard and direct injection of a fluid based on engine operating conditions and the composition of the injected fluid. One or more engine parameters, such as EGR, VCT, boost, throttle position, are coordinated with the direct injection to reduce torque and EGR transients.

Methods and systems are provided for accurately determining the composition of a knock control fluid using sensors already present in the engine system. An intake or an exhaust oxygen sensor is used to estimate the water and the alcohol content of a knock control fluid that is direct injected into an engine cylinder responsive to an indication of abnormal combustion. A change in the pumping current of the oxygen sensor due to the water content of the knock control fluid is distinguished from a change in the pumping current of the oxygen sensor due to the alcohol content of the knock control fluid.

Methods and systems are provided for adjusting an ignition timing of an internal combustion engine responsive to a biasing force of a pressure-reactive piston. In one example, an engine may include a pressure-reactive piston having a top wall biased away from a piston base by a pressure of gas contained within the base. An ignition timing of a combustion chamber including the piston is adjusted responsive to an estimated biasing force of the gas against the top wall.

A control apparatus for an internal combustion engine, includes circuitry. The circuitry is configured to control a ratio of an amount of low octane number fuel to be supplied to a cylinder to a total amount of the low octane number fuel and a high octane number fuel to be supplied to the cylinder in order to control an overall octane number of fuel to be supplied to the cylinder. The high octane number fuel has a second octane number higher than a first octane number of the low octane number fuel. The circuitry is configured to calculate a maximum octane number of the fuel to be supplied into the cylinder. The circuitry is configured to restrict a power generated by the internal combustion engine based on the maximum octane number.