Internal combustion engine

An internal combustion engine comprising:

• a crankcase;
• a crankshaft adapted to rotate about a crankshaft axis and disposed at least in part in the crankcase;
• a cylinder block connected to the crankcase, the cylinder block defining a cylinder having a cylinder axis;
• a cylinder head connected to the cylinder block, the cylinder block disposed between the cylinder head and the crankcase,
• a piston disposed in the cylinder and operatively connected to the crankshaft, the cylinder, the cylinder head and the piston together defining at least one combustion chamber;
• an intake port defined by the cylinder block for allowing at least one combustion component to enter the combustion chamber;
• an exhaust port defined by the cylinder block, on an exhaust side of the internal combustion engine, for allowing exhaust gas to exit the combustion chamber through an exhaust passage extending from the exhaust port in the cylinder block;
• a first auxiliary exhaust port defined by the cylinder block and a second auxiliary exhaust port defined by the cylinder block, the first and second auxiliary exhaust ports positioned circumferentially one on either side of the exhaust port and connected to the cylinder for allowing exhaust gas to exit the combustion chamber;
• a first auxiliary exhaust passage in the cylinder block extending from the first auxiliary port;
• a second auxiliary exhaust passage in the cylinder block extending from the second auxiliary port;
• a cooling jacket defined in the cylinder block for cooling at least an exhaust side of the cylinder, the cooling jacket at least partially surrounding the cylinder and including a first cooling passage positioned between the exhaust passage and the first auxiliary exhaust passage, and a second cooling passage positioned between the exhaust passage and the second auxiliary exhaust passage, the cooling jacket on at least the exhaust side of the cylinder comprising an upper portion and a lower portion, the upper and lower portions of the cooling jacket being in fluid communication with each other via at least one of the first cooling passage and the second cooling passage.