A method to control the combustion of an internal combustion engine comprising a number of cylinders and a low-pressure EGR circuit (EGR LP); 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 quantity (R EGR-OL) representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in an intake duct by means of a control map and depending on the rotation speed (n) and the intake efficiency (η ASP): determining a first closed-loop quantity (ΔR EGR-KNOCK) representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in the intake duct depending on a quantity (E det, MAPO) indicating the knocking energy; calculating the objective value (R EGR-obj) of said quantity representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in the intake duct through the sum of the first open-loop quantity (R EGR-OL) and the first closed-loop quantity (ΔR EGR-KNOCK); determining a quantity (R EGR) representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in an intake duct depending on the objective value (R EGR-obj) of said quantity; determining an open-loop 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 the intake efficiency (η ASP); determining, in a designing phase, a combustion model providing a spark advance value (SA model) depending on said quantity (R EGR), rotation speed (n), intake efficiency (ηASP) and open-loop combustion index, wherein the combustion model is expressed by means of a parabola formulated as follows: SA model = a 2 * MFB 50 2 + a 1 * MFB 50 + a 0 MFB50 combustion index; SA model spark advance value provided by the combustion model; wherein the a i coefficients are expressed as follows: a i = f i η ASP, n * g i R EGR, η ASP i = 0, 1, 2 R EGR quantity representing the incidence of the low-pressure EGR circuit (EGR LP); n rotation speed, ηASP intake efficiency; calculating a first closed-loop spark advance (ΔSA MFB50), which is suited to optimize the efficiency of the internal combustion engine, depending on the open-loop combustion index; calculating a second closed-loop spark advance (ΔSA KNOCK), which is suited to avoid the occurrence of knocking phenomena, depending on a 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 spark advance (ΔSA MFB50) and of the second closed-loop spark advance (ΔSA KNOCK). acquiring the rotation speed (n) and the intake efficiency (η ASP) of the internal combustion engine; determining a first open-loop quantity (R EGR-OL) representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in an intake duct by means of a control map and depending on the rotation speed (n) and the intake efficiency (η ASP): determining a first closed-loop quantity (ΔR EGR-KNOCK) representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in the intake duct depending on a quantity (E det, MAPO) indicating the knocking energy; calculating the objective value (R EGR-obj) of said quantity representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in the intake duct through the sum of the first open-loop quantity (R EGR-OL) and the first closed-loop quantity (ΔR EGR-KNOCK); determining a quantity (R EGR) representing the incidence of the low-pressure EGR circuit (EGR LP) on the gas mixture flowing in an intake duct depending on the objective value (R EGR-obj) of said quantity; determining an open-loop 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 the intake efficiency (η ASP); determining, in a designing phase, a combustion model providing a spark advance value (SA model) depending on said quantity (R EGR), rotation speed (n), intake efficiency (ηASP) and open-loop combustion index, wherein the combustion model is expressed by means of a parabola formulated as follows: SA model = a 2 * MFB 50 2 + a 1 * MFB 50 + a 0 MFB50 combustion index; SA model spark advance value provided by the combustion model; wherein the a i coefficients are expressed as follows: a i = f i η ASP, n * g i R EGR, η ASP i = 0, 1, 2 R EGR quantity representing the incidence of the low-pressure EGR circuit (EGR LP); n rotation speed, ηASP intake efficiency; calculating a first closed-loop spark advance (ΔSA MFB50), which is suited to optimize the efficiency of the internal combustion engine, depending on the open-loop combustion index; calculating a second closed-loop spark advance (ΔSA KNOCK), which is suited to avoid the occurrence of knocking phenomena, depending on a 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 spark advance (ΔSA MFB50) and of the second closed-loop spark advance (ΔSA KNOCK).