An internal combustion engine (1) includes: an exhaust gas recirculation unit equipped with an exhaust gas recirculation control valve (9); a crank angle sensor (11) that detects an indicated mean effective pressure fluctuation rate (cPi) as an indicator of combustion stability of the internal combustion engine (1); and a controller (10) that corrects the EGR rate of the exhaust gas recirculation unit based on the combustion stability. The controller (10) is configured to: increase-correct the EGR rate by a predetermined amount when the state where the indicated mean effective pressure fluctuation rate (cPi) is lower than a threshold value continues for a predetermined number of cycles; and decrease-correct the EGR rate by a predetermined amount immediately when the indicated mean effective pressure fluctuation rate (cPi) is higher than or equal to the threshold value.

Provided is an internal combustion engine control unit that controls an engine by detecting combustion characteristics with a simple configuration robust to disturbance such as noise. Therefore, the internal combustion engine control unit (ECU 12) of the present embodiment includes a rotational speed calculation unit 122a that calculates a crank rotational speed of an internal combustion engine (engine 1); an extreme value timing calculation unit 122b that calculates an extreme value timing of the crank rotational speed calculated by the rotational speed calculation unit 122a; and a combustion state estimation unit (combustion phase calculation unit 122c) that estimates a combustion state based on the extreme value timing of the crank speed calculated by the extreme value timing calculation unit 122b.

Provided is an engine control device which controls at least an intake valve, an exhaust valve, and a fuel injection valve injecting a fuel into an intake pipe such that internal EGR is realized, in which timing of opening and closing of the intake valve is set to be later in comparison with a reference operation state which is a first operation state and timing of closing of the exhaust valve is set to be earlier in comparison with the reference operation state, and the fuel injection valve is caused to inject the fuel in a period which is: after a piston starts to rise which had been passed through a bottom dead center for the first time after an exhaust stroke is finished, which is followed by closing of the intake valve; and before the intake valve is opened.

A system and method of inducing an operational response change in an operating direct-injection internal combustion engine is provided such that the engine includes a cylinder into which liquid fuel injection is directly performed. The method starts by operating the direct-injection engine using a start of injection (SOI) protocol. At some point during operation, it is determined that a change is desired for a first parameter of engine operation that is at least partially a function of a charge provided to the cylinder (such as the torque output). In response an operational response in the engine is induced by altering the SOI protocol via a first SOI alteration that alters the volumetric efficiency of the cylinder and changes the first parameter.

A system and method of inducing an operational response change in an operating direct-injection internal combustion engine is provided such that the engine includes a cylinder into which liquid fuel injection is directly performed. The method starts by operating the direct-injection engine using a start of injection (SOI) protocol. At some point during operation, it is determined that a change is desired for a first parameter of engine operation that is at least partially a function of a charge provided to the cylinder (such as the torque output). In response an operational response in the engine is induced by altering the SOI protocol via a first SOI alteration that alters the volumetric efficiency of the cylinder and changes the first parameter.

A temperature sensor and a relative humidity sensor are placed in an environment allowing air to flow and are displaced in an upstream-downstream direction of the airflow. An absolute humidity acquisition unit acquires absolute humidity of air from outputs from the temperature sensor and the relative humidity sensor. A delay adjustment unit delays an output from one of the temperature sensor and the relative humidity sensor placed upstream and to reconcile change-behaviors of outputs from the temperature sensor and the relative humidity sensor in response to a state change in air. The absolute humidity acquisition unit acquires the absolute humidity based on the output from the other of the temperature sensor and the relative humidity sensor placed downstream and an output acquired from the one sensor placed upstream and delayed in the delay adjustment unit.

A temperature sensor differs from a relative humidity sensor in responsiveness when the temperature of air changes. An absolute humidity acquisition unit acquires absolute humidity of air from outputs from the temperature sensor and the relative humidity sensor. A delay adjustment unit is to delay an output from one of the temperature sensor and the relative humidity sensor, which is a high response sensor having a higher responsiveness, and to reconcile change-behaviors of the output from the temperature sensor and the output from the relative humidity sensor in response to a temperature change in air. The absolute humidity acquisition unit acquires the absolute humidity based on the output from the other of the temperature sensor and the relative humidity sensor, which is a low response sensor having a lower responsiveness, and the sensor signal, which is from the high response sensor and delayed in the delay adjustment unit.

A method for reducing NOx emissions during operation of an internal combustion engine in commerce which, when burning hydrocarbon fuel as a primary fuel, in the absence of any secondary fuel, has a characteristic stoichiometric ration. The method includes the following: in the absence of electrolytic activity, providing and entraining a quenching species in a gaseous medium and then interacting the quenching species with constituents present during oxidation of the primary fuel in a combustion chamber of the engine.

A method for reducing NOx emissions during operation of an internal combustion engine in commerce which, when burning hydrocarbon fuel as a primary fuel, in the absence of any secondary fuel, has a characteristic stoichiometric ration. The method includes the following: in the absence of electrolytic activity, providing and entraining a quenching species in a gaseous medium and then interacting the quenching species with constituents present during oxidation of the primary fuel in a combustion chamber of the engine.

An internal combustion engine including a fuel reformation unit that generates reformed fuel based on liquid fuel and higher in octane rating than the liquid fuel and introduces the generated reformed fuel to an output cylinder. The fuel reformation unit includes a first fuel reformer that includes a reciprocal mechanism where a piston reciprocates in a cylinder, a second fuel reformer that includes a reformation catalyst, and a reformed gas passage that connects the first and second fuel reformers together. First reformed gas discharged from the first fuel reformer is introduced to the second fuel reformer through the reformed gas passage.