- A method to control the combustion of an internal combustion engine comprising a number of cylinders and a water collection and injection system to introduce water into the internal combustion engine; the method comprises the steps of: acquiring the rotation speed (n) and the intake efficiency (η ASP) of the internal combustion engine; determining a first open-loop contribution (R OL) of a water rate equal to the ratio between the injected water mass (m H2O) and the injected fuel mass (m FUEL) by means of a control map and depending on the rotation speed (n) and on the intake efficiency (η ASP); determining a first closed-loop contribution (ΔR KNOCK) of the water rate depending on a quantity (E det, MAPO) indicating the knocking energy; calculating the objective value (R obj) of the water rate through the sum of the first open-loop contribution (R OL) and of the first closed-loop contribution (ΔR KNOCK); determining an open-loop contribution (MFB50 OL) of a combustion index representing the engine angle where, inside the cylinder, 50% of the fuel mass was burnt by means of a control map and depending on the rotation speed (n) and on the intake efficiency (η ASP); determining, in a designing phase, a combustion model providing a spark advance value (SA model) depending on the objective value (R obj) of the water rate, on the rotation speed (n), on the intake efficiency (η ASP) and on the open-loop contribution (MFB50 OL) of the combustion index; calculating a first closed-loop contribution (ΔSA MFB50) of the spark advance, which is suited to optimize the efficiency of the internal combustion engine, depending on the combustion index; calculating a second closed-loop contribution (ΔSA KNOCK) of the spark advance, which is suited to avoid the occurrence of knocking phenomena, depending on the quantity (E det, MAPO) indicating the knocking energy; and calculating the objective value (SA obj) of the spark advance angle to be operated through the sum of the spark advance value (SA model) provided by the combustion model, of the first closed-loop contribution (ΔSAMFB50) of the spark advance and of the second closed-loop contribution (ΔSA KNOCK) of the spark advance. acquiring the rotation speed (n) and the intake efficiency (η ASP) of the internal combustion engine; determining a first open-loop contribution (R OL) of a water rate equal to the ratio between the injected water mass (m H2O) and the injected fuel mass (m FUEL) by means of a control map and depending on the rotation speed (n) and on the intake efficiency (η ASP); determining a first closed-loop contribution (ΔR KNOCK) of the water rate depending on a quantity (E det, MAPO) indicating the knocking energy; calculating the objective value (R obj) of the water rate through the sum of the first open-loop contribution (R OL) and of the first closed-loop contribution (ΔR KNOCK); determining an open-loop contribution (MFB50 OL) of a combustion index representing the engine angle where, inside the cylinder, 50% of the fuel mass was burnt by means of a control map and depending on the rotation speed (n) and on the intake efficiency (η ASP); determining, in a designing phase, a combustion model providing a spark advance value (SA model) depending on the objective value (R obj) of the water rate, on the rotation speed (n), on the intake efficiency (η ASP) and on the open-loop contribution (MFB50 OL) of the combustion index; calculating a first closed-loop contribution (ΔSA MFB50) of the spark advance, which is suited to optimize the efficiency of the internal combustion engine, depending on the combustion index; calculating a second closed-loop contribution (ΔSA KNOCK) of the spark advance, which is suited to avoid the occurrence of knocking phenomena, depending on the quantity (E det, MAPO) indicating the knocking energy; and calculating the objective value (SA obj) of the spark advance angle to be operated through the sum of the spark advance value (SA model) provided by the combustion model, of the first closed-loop contribution (ΔSAMFB50) of the spark advance and of the second closed-loop contribution (ΔSA KNOCK) of the spark advance.