Abstract: A method of controlling a four stroke internal combustion engine having at least one combustion chamber, the or each combustion chamber having at least one exhaust valve, the method including varying the timing of the closure of the or each exhaust valve with respect to the crank angle of the engine by advancing the exhaust valve closure at least under certain engine conditions in response to an increased engine load, and/or delaying the exhaust valve closure at least under certain conditions in response to a decreased engine load.

Abstract: Disclosed is an internal combustion engine (20) having a combustion chamber (36), a pre-combustion chamber (38) communicating with the combustion chamber (36), injection means (70) located and arranged to periodically deliver controlled amounts of fuel and air into the pre-combustion chamber (38) in a manner and orientation to direct a fuel spray to pass through the pre-combustion chamber (38) into the combustion chamber (36), and ignition means (63) positioned relative to the pre-combustion chamber (38) and operably arranged to ignite the fuel spray.

Abstract: A method of operating an internal combustion engine comprising retarding the ignition of a gas/fuel mixture within at least one cylinder of the engine to after top dead center (ATDC) in respect of the combustion cycle of said at least one cylinder of the engine. While the ignition is so retarded, the fuelling rate of said at least one cylinder is increased to a level higher than that required when the engine is operating normally.