Intake air/exhaust gas flow control is performed in an partial load range of an engine such that burned gas which is discharged from an exhaust stroke side preceding cylinder of a pair of cylinders having an overlapping exhaust stroke and intake stroke is introduced into an intake stroke side following cylinder through an intercylinder gas channel. In an operating range set as a special operation mode, a combustion condition controller executes control such that combustion is performed in the following cylinder by means of compression ignition. In an operating condition in which knocking is likely to occur within the compression ignition range of the following cylinder, control is executed by a fuel injection controller such that the timing of fuel injection into the following cylinder is retarded relative to that of an operating condition in which knocking is unlikely to occur.
For the purpose of improving the fuel efficiency by lean combustion and enhancing the fuel efficiency improvement effects by performing compression ignition efficiently in some cylinders, a multi-cylinder spark ignition engine is constructed such that exhaust gas, that is exhausted from preceding cylinders 2A, 2D on the exhaust stroke side among pairs of cylinders whose exhaust stroke and intake stroke overlap in a low load, low rotational speed region, is directly introduced through an inter-cylinder gas passage 22 into following cylinders 2B, 2C on the intake stroke side and only gas exhausted from the following cylinders 2B, 2C is fed to an exhaust passage 20, which is provided with a three-way catalyst 24. Combustion controller is provided that controls the combustion of each of the cylinders such that combustion is conducted by forced ignition in a condition in which the air/fuel ratio is a lean air/fuel ratio which is larger by a prescribed amount than the stoichiometric air/fuel ratio in the preceding cylinders 2A, 2D and, in the following cylinders 2B, 2C, fuel is supplied to burnt gas of lean air/fuel ratio introduced from the preceding cylinders 2A, 2D and combustion is conducted by compression ignition.
The invention is intended to provide improved emission-cleaning performance by use of a three-way catalyst alone, without the need for a lean NOx catalyst, while ensuring a fuel economy improvement effect of lean burn operation. A multicylinder spark-ignition engine is constructed such that, in a pair of preceding and following cylinders whose exhaust and intake strokes overlap each other, burned gas discharged from the preceding cylinder (2A, 2D) which is currently in the exhaust stroke is introduced directly into the following cylinder (2B, 2C) which is currently in the intake stroke through an intercylinder gas channel (22) and gas discharged from only the following cylinder (2B, 2C) is led to an exhaust passage (20) provided with a three-way catalyst (24) in a low-load, low-speed operating range. Fuel supply to the individual cylinders is controlled in such a manner that combustion in the preceding cylinder (2A, 2D) is made under lean mixture conditions at an air-fuel ratio larger than the stoichiometric air-fuel ratio by a specific amount and combustion in the following cylinder (2B, 2C) is made under conditions of the stoichiometric air-fuel ratio created by supplying fuel to the burned gas introduced from the preceding cylinder (2A, 2D).
The present invention relates to a method of injecting fuel into the combustion chamber (16) of a cylinder of a direct-injection four-stroke internal-combustion engine, notably of diesel type, that can run according to a homogeneous combustion mode and according to a conventional combustion mode.According to the invention, this method consists, for the conventional combustion mode of the engine, in feeding into this chamber a first amount of fuel in the vicinity of the top dead centre of the piston at the beginning of the intake phase and another quantity of fuel in the vicinity of the top dead centre of this piston at the end of the compression phase.
