A rotary internal combustion engine comprising: a rotor body; and a stator body, wherein the stator body comprises: two axially spaced apart end walls; a peripheral wall extending between the end walls and defining an internal cavity therewith, the cavity having an epitrochoid shape defining two lobes, wherein the cavity receives the rotor body rotatable within the cavity and defines three working chambers of variable volume in the cavity between the rotor body and the stator body, the volume of each of the three working chambers is configured to vary between a minimum volume and a maximum volume, a difference between the maximum volume and the minimum volume defining a displacement volume; and an insert (34; 134; 234) in the peripheral wall of the stator body, the insert (34; 134; 234) being made of a material having a greater heat resistance than that of the peripheral wall, the insert (34; 134; 234) having a subchamber defined therein and having an inner surface (66; 166; 266) bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface (66; 166; 266) and having a shape forming a reduced cross-section adjacent the opening, at least one of the insert (34; 134; 234) and the peripheral wall having a pilot fuel injector elongated hole defined therethrough communicating with the subchamber and sized to receive a pilot fuel injector therein, at least one of the insert (34; 134; 234) and the peripheral wall having an ignition element elongated hole defined therethrough communicating with the subchamber and sized to receive an ignition element therein, and the peripheral wall having a main fuel injector elongated hole defined therethrough spaced apart from the insert (34; 134; 234) and sized to receive a main fuel injector therein, characterised in that the subchamber has a volume of at least 0.5% of the displacement volume and up to 3.5% of the displacement volume. a rotor body; and a stator body, wherein the stator body comprises: two axially spaced apart end walls; a peripheral wall extending between the end walls and defining an internal cavity therewith, the cavity having an epitrochoid shape defining two lobes, wherein the cavity receives the rotor body rotatable within the cavity and defines three working chambers of variable volume in the cavity between the rotor body and the stator body, the volume of each of the three working chambers is configured to vary between a minimum volume and a maximum volume, a difference between the maximum volume and the minimum volume defining a displacement volume; and an insert (34; 134; 234) in the peripheral wall of the stator body, the insert (34; 134; 234) being made of a material having a greater heat resistance than that of the peripheral wall, the insert (34; 134; 234) having a subchamber defined therein and having an inner surface (66; 166; 266) bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface (66; 166; 266) and having a shape forming a reduced cross-section adjacent the opening, at least one of the insert (34; 134; 234) and the peripheral wall having a pilot fuel injector elongated hole defined therethrough communicating with the subchamber and sized to receive a pilot fuel injector therein, at least one of the insert (34; 134; 234) and the peripheral wall having an ignition element elongated hole defined therethrough communicating with the subchamber and sized to receive an ignition element therein, and the peripheral wall having a main fuel injector elongated hole defined therethrough spaced apart from the insert (34; 134; 234) and sized to receive a main fuel injector therein, characterised in that the subchamber has a volume of at least 0.5% of the displacement volume and up to 3.5% of the displacement volume. two axially spaced apart end walls; a peripheral wall extending between the end walls and defining an internal cavity therewith, the cavity having an epitrochoid shape defining two lobes, wherein the cavity receives the rotor body rotatable within the cavity and defines three working chambers of variable volume in the cavity between the rotor body and the stator body, the volume of each of the three working chambers is configured to vary between a minimum volume and a maximum volume, a difference between the maximum volume and the minimum volume defining a displacement volume; and an insert (34; 134; 234) in the peripheral wall of the stator body, the insert (34; 134; 234) being made of a material having a greater heat resistance than that of the peripheral wall, the insert (34; 134; 234) having a subchamber defined therein and having an inner surface (66; 166; 266) bordering the cavity, the subchamber communicating with the cavity through at least one opening defined in the inner surface (66; 166; 266) and having a shape forming a reduced cross-section adjacent the opening, at least one of the insert (34; 134; 234) and the peripheral wall having a pilot fuel injector elongated hole defined therethrough communicating with the subchamber and sized to receive a pilot fuel injector therein, at least one of the insert (34; 134; 234) and the peripheral wall having an ignition element elongated hole defined therethrough communicating with the subchamber and sized to receive an ignition element therein, and the peripheral wall having a main fuel injector elongated hole defined therethrough spaced apart from the insert (34; 134; 234) and sized to receive a main fuel injector therein, characterised in that the subchamber has a volume of at least 0.5% of the displacement volume and up to 3.5% of the displacement volume.