A compression-ignition engine control system is provided, which includes an intake phase-variable mechanism and a controller. The controller controls the intake phase-variable mechanism to form a gas-fuel ratio (G/F) lean environment in which burnt gas remains inside a cylinder and an air-fuel ratio is near a stoichiometric air-fuel ratio, and controls the spark plug to spark-ignite the mixture gas to combust in a partial compression-ignition combustion. The controller controls the intake phase-variable mechanism to retard, as an engine speed increases at a constant engine load, an intake valve close timing on a retarding side of BDC of intake stroke and an intake valve open timing on an advancing side of TDC of exhaust stroke, and controls the intake phase-variable mechanism so that a change rate in the intake valve open timing according to the engine speed becomes larger in a high engine speed range.

In a predetermined operating region, a fuel injection valve executes a second injection to inject fuel into a cylinder in a compression stroke, and a first injection to inject fuel into the cylinder 2 in the compression stroke or an intake stroke before the second injection. When a purge is executed, the total quantity of fuel to be injected by the fuel injection valve into the cylinder is reduced more than when the purge is not executed, and a fuel reduction quantity of the second injection is made smaller than a fuel reduction quantity of the first injection.

A direct fuel injection engine including an ignition plug and a fuel injection valve arranged to be capable of injecting a fuel directly in a cylinder is controlled. The engine has a predetermined operation region in which an excess air ratio of an air-fuel mixture is set in a vicinity of 2. In a first region on a low load side of the predetermined operation region, a homogenous air-fuel mixture having the excess air ratio at a first predetermined value in the vicinity of 2 is formed upon combustion, and in a second region on a load side higher than the first region, a stratified air-fuel mixture having the excess air ratio at a second predetermined value in the vicinity of 2 is formed upon combustion.

A method for fouling an injector of a gasoline direct injection engine, includes the steps of operating the direct injection engine on at least a first stationary engine mode which is defined by a pre-established engine load and a pre-established engine speed. Both the pre-established engine load and the speed are within 35% and 65% of their maximum values, this at least first stationary engine mode being characterized by high particulate matter generation. The direct injection engine is operated on the at least first engine mode for less than ten hours.

A method for evaluating the fouling effect of a gasoline formulation in a gasoline direct injection engine uses the above-described fouling method.

A control device for an engine is provided, which includes a fuel injector attached to the engine, a spark plug disposed to be oriented into a combustion chamber, a swirl control valve provided in an intake passage, and a controller connected to the fuel injector, the spark plug, and the swirl control valve and configured to control the fuel injector, the spark plug, and the swirl control valve. The swirl control valve closes in a given operating state of the engine. The fuel injector injects fuel after the swirl control valve is closed, between intake stroke and an intermediate stage of compression stroke. The fuel injector injects the fuel after the first fuel injection. The spark plug performs the ignition after the second fuel injection so that the mixture gas starts combustion by flame propagation and then unburned mixture gas self-ignites.

A direct fuel injection engine including an ignition plug and a fuel injection valve arranged to be capable of injecting a fuel directly in a cylinder is controlled. The engine has a predetermined operation region in which an excess air ratio of an air-fuel mixture is set in a vicinity of 2. In a first region on a low load side of the predetermined operation region, a homogenous air-fuel mixture having the excess air ratio at a first predetermined value in the vicinity of 2 is formed upon combustion, and in a second region on a load side higher than the first region, a stratified air-fuel mixture having the excess air ratio at a second predetermined value in the vicinity of 2 is formed upon combustion.

As a control method for internal combustion engine, a part of a low-medium revolution speed/low-medium load region of an internal combustion engine is set as a lean combustion region, homogeneous combustion is performed in an operating region within the lean combustion region where a load is relatively low, by injecting fuel at least once between an intake stroke and the first half of a compression stroke to form a homogeneous air-fuel mixture in a combustion chamber, and stratified combustion is performed in an operating region within the lean combustion region where the load is relatively high, by injecting the fuel at least once, respectively, between the intake stroke and the first half of the compression stroke as well as in the second half of the compression stroke to form a stratified air-fuel mixture in the combustion chamber. In this control method, ignition energy supplied to an ignition plug when the stratified combustion is performed is controlled to be smaller than ignition energy supplied to the ignition plug when the homogeneous combustion is performed.

In a control method for internal combustion engine for forming a stratified air-fuel mixture in a combustion chamber and performing stratified combustion by injecting fuel at least once each time between an intake stroke and the first half of a compression stroke and in the second half of the compression stroke, spark ignition is started by flowing a relatively large discharge current into the ignition plug when flow energy around the ignition plug is increased by energy of a fuel spray injected in the second half of the compression stroke and, thereafter, the discharge current is made relatively smaller and discharged for a predetermined period.

In some examples, a system including one or more processors may receive sensor data from one or more sensors indicating one or more engine parameters of an engine including a combustion chamber. Based on the sensor data, the system may determine a homogeneity index indicative of a homogeneity of an air-fuel mixture within the combustion chamber. Furthermore, the system may determine an estimated amount of NOx in the exhaust gas based at least in part on the homogeneity index. In addition, based at least partially on the estimated amount of NOx in the exhaust gas, the system may send an instruction to control an engine component.

In a first region on a low load side of an operation region of a direct fuel injection engine, homogenous combustion is performed, while, in a second region of the operation region on a load side higher than the first region, stratified combustion is performed. In the stratified combustion, a fuel is dispersed in a cylinder by a first injection operation and a fuel is unevenly distributed in a vicinity of the ignition plug by a second injection operation. Shift control by the stratified combustion is executed at a time of shifting when an operation state of the engine has shifted from the first region to the second region, and in the shift control, a fuel in an amount larger than a target amount of the second injection operation in the second region is injected by the second injection operation and then, an injection amount of the second injection operation is decreased toward the target amount.