Control device for engine

A control device for an engine in which partial compression-ignition combustion including spark ignition (SI) combustion performed by forcibly combusting a portion of mixture gas inside a cylinder followed by compression ignition (CI) combustion performed by causing the rest of the mixture gas inside the cylinder to self-ignite is executed within a part of an operating range of the engine, comprising:

• a detector configured to detect a parameter related to noise caused by the combustion inside the cylinder;
• a memory configured to store a characteristic defining a relationship between a start timing of the CI combustion and a combustion noise index;
• and
• a processor configured to:
• specify a given combustion noise index value based on the detection value of the detector;
• and
• control the start timing of the CI combustion based on the characteristic and the combustion noise index value.

A method of controlling a compression-ignition engine including a cylinder, a piston, a cylinder head, a combustion chamber formed by the cylinder, the piston, and the cylinder head, a spark plug disposed in the combustion chamber, and a fuel injection valve disposed to be oriented into the combustion chamber, comprising:

• detecting an in-cylinder pressure that is a pressure inside the combustion chamber;
• calculating, based on the detected in-cylinder pressure, a first combustion noise index value that is an in-cylinder pressure level at a given high frequency, and a second combustion noise index value that is an in-cylinder pressure level at a given low frequency;
• calculating a limit value of a start timing of the CI combustion based on the first combustion noise index value and the second combustion noise index value;
• setting an ignition timing so that the start timing of the CI combustion does not advance beyond the limit value;
• and
• causing the spark plug to ignite at the set ignition timing.