Abstract: The two-stroke engine includes at least one cylinder, a piston reciprocable within the cylinder and a cylinder head which contains at least one exhaust port which is controlled by a poppet valve and at least two inlet ports which are controlled by respective poppet valves and are connected to respective inlet ducts. The inlet ports are of directed type with the axes of the inlet ducts being convergent in the direction of flow whereby the air flowing through them into the cylinder flows preferentially generally towards the cylinder axis. The axes of the inlet ducts pass substantially through the cylinder axis where the air flows through the inlet ports merged to form a single air flow on or adjacent the cylinder axis.

Abstract: A two-stroke engine includes at least one cylinder, a piston reciprocable within the cylinder and a cylinder head which contains at least one exhaust port and at least two inlet ports which are controlled by respective poppet valves. The cylinder defines a combustion chamber of pent-roof form with which the inlet and exhaust ports communicate. The inlet ports are of directed type whereby, in use, the flow of air through them is generally away from the exhaust valve(s) and thus flows down the wall of the cylinder adjacent the inlet port. The axes of the inlet ducts converge in the direction of flow through them and the axis of each inlet defines angle of at least 20.degree. with that of the other inlet duct when viewed in the direction of the cylinder axis.

Abstract: A two-stroke engine comprises a cylinder which accommodates a piston and which has inlet and outlet ports, means for injecting fuel into the cylinder and control means for controlling the amount of fuel injected. The engine also includes a vent passage communicating with the interior of the cylinder and a first valve which is arranged to prevent communication between the interior of the cylinder and the vent passage and is connected to be opened and closed in synchronism with movement of the piston. Situated in the vent passage downstream of the first valve is a second throttling valve which is coupled to the control means and is arranged to be opened to an increasing extent to permit an increasing proportion of the inlet charge to be discharged as the control means is operated to reduce the amount of fuel which is injected into the cylinder thereby achieving homogeneous combustion at a constant air fuel ratio.

Abstract: A two-stoke engine comprises a cylinder accommodating a piston and having an air inlet port and an exhaust port. The exhaust port communicates with an exhaust system which includes a reduction catalyst and an oxidation catalyst. The exhaust system includes two exhaust flow paths in parallel, the first of which includes the reduction catalyst and the second of which bypasses the reduction catalyst, the downstream ends of the two flow paths being connected together upstream of the oxidation catalyst. The exhaust port is controlled by the piston or by poppet valves so that as the piston performs its downstroke the initial flow of exhaust gas is substantially through the first flow path and the subsequent flow of exhaust gas is substantially through the second flow path.