Premixed compression ignition type engine and its operation control method

摘要

PROBLEM TO BE SOLVED: To provide a technique suppressing deterioration of cycle variations in association with variations of an EGR ratio when combustion timing control using EGR ratio adjustment means is performed in a homogeneous charge compression ignition type engine.SOLUTION: In addition to combustion timing control for activating EGR ratio adjustment means 40 and controlling an EGR ratio being a recirculation ratio of exhaust gas to a combustion chamber 10 so as to cause combustion timing of an air-fuel mixture M in the combustion chamber 10 detected by combustion timing detection means 51 to be predetermined target combustion timing, specific hydrocarbon content control for activating specific hydrocarbon content adjustment means 60 in response to a state of the EGR ratio adjustment means 40 and varying a specific hydrocarbon content in a form that the specific hydrocarbon content being a content of specific hydrocarbon consisting of at least one of ethane and propane in the air-fuel mixture is increased as the EGR ratio is increased is executed.