Auto-ignition timing control and calibration method

A method of controlling an internal combustion engine when operating in a controlled auto-ignition mode, the method comprising the steps of:

• before the commencement of an engine compression phase determining a target crank angle from a predetermined data table and from current engine operating conditions, the data table providing a plurality of auto-ignition timing crank angle data relating to a plurality of engine operating conditions;
• determining a plurality of engine operating parameters;
• iteratively performing the steps of
• (i) utilizing the plurality of engine operating parameters, computing the crank angle during the compression phase of the engine cycle at which a target compression temperature would be reached by the combustible charge;
• (ii) comparing the predicted crank angle with the target crank angle;
• (iii) modifying the computational value of at least one of the settable engine operating parameters;
• (iv) returning to step (i), until a combination of parameters is found which would result in the target compression temperature being reached at a predicted crank angle matching the target crank angle;
• and
• setting at least one of the actual engine operating parameters for the engine cycle in accordance with the final values ascertained by the iterative calculation process.

A method of controlling a spark ignition internal combustion engine having variable compression ratio, the method comprising the steps of:

• determining a plurality of engine operating parameters;
• iteratively performing the steps of
• (i) utilizing the plurality of engine operating parameters, computing a predicted compression temperature which would be reached by the combustible charge at a target crank angle during the compression phase of the engine;
• (ii) comparing the predicted compression temperature with a threshold temperature, the threshold temperature being lower than the auto-ignition temperature of the charge;
• (iii) modifying the value of at least one of the operating parameters;
• (iv) returning to step (i), until a combination of parameters is found which would result in the predicted compression temperature not exceeding the threshold temperature;
• and,
• setting at least one of the actual engine operating parameters for the engine cycle in accordance with the final values ascertained by the iterative calculation process such as to prevent engine knock.