Process and an apparatus to adjust the ignition timing of an internal combustion engine

An apparatus (11) to adjust the ignition timing of an air-fuel mixture in a combustion chamber (6) of an internal combustion engine (2), the apparatus comprising

• first determining means (T1) to determine a first quantity indicative of a pressure of the mixture for a cycle of the engine,
• second determining means (T2) to determine a second quantity indicative of a speed of the engine,
• third determining means (T3) to determine a third quantity indicative of a first temperature of a conditioning fluid used to thermally condition the combustion chamber (6), at a zone of heat exchange between the engine (2) and the conditioning fluid,
• ignition means (12) connectable to the engine (2) to ignite the mixture in the combustion chamber (6),
• a control unit (ECU) adapted to be coupled to each one of said first, second and third determining means (T1, T2, T3) so as to extract corresponding information concerning the first, second and third determined quantity as well as adapted to be coupled to said ignition means (12) so as to control the ignition of the mixture,
• wherein the control unit (ECU) stores a heat exchange mathematical model for the combustion chamber (6), the model mapping the set of three quantities, consisting of the first, the second and the third quantity, onto a fourth quantity indicative of a second temperature of a wall portion (3, 5) around the combustion chamber (6),
• wherein the control unit (ECU) is programmed to estimate the fourth quantity by means of said extracted information and by means of the mathematical model as well as to adjust the ignition timing by controlling the ignition means (12) as a function of the fourth estimated quantity.