To balance a low-temperature scavenging effect and a high-temperature scavenging effect. A scavenging system applicable to a leading-air type two-stroke air-cooled engine has a low-temperature scavenging passage and a high-temperature scavenging passage. The low-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. The high-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. An air is filled through a piston groove into the passages. The low-temperature scavenging passage has a relatively small capacity. The high-temperature scavenging passage has a relatively large capacity.

To balance a low-temperature scavenging effect and a high-temperature scavenging effect. A scavenging system applicable to a leading-air type two-stroke air-cooled engine has a low-temperature scavenging passage and a high-temperature scavenging passage. The low-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. The high-temperature scavenging passage has first and second passages and includes scavenging ports at upper end parts thereof. An air is filled through a piston groove into the passages. The low-temperature scavenging passage has a relatively small capacity. The high-temperature scavenging passage has a relatively large capacity.

An opposed piston engine includes approximately spherical combustion chamber formed by the two opposed pistons in a single cylinder and an intake manifold including gas hooks. The combustion chamber has a small cone shaped extension on each side leading to each of two opposed injectors located in the cylinder wall where the two pistons meet at the top of their stroke. The combustion chamber configuration reduces the surface area of the chamber and increases the burn length by a significant amount compared to known designs. The gas hooks in the intake manifold restrict the flow of exhaust gases into the intake manifold long enough for the pressure in the cylinder to blow down and the exhaust gasses to attain high velocity passing out through the exhaust manifold, allowing the intake ports to be uncovered before the exhaust ports.

To allow an intake negative pressure to directly act on a fuel outlet formed on a nozzle tube, and to guide a fuel discharged from the fuel outlet in the nozzle tube to the fuel-air mixture passage. A rotary carburetor (200) has a guide plate member (42) downstream of a fuel outlet (30) located in a through-hole (14). The guide plate member (42) has both side edges (42b) away from an inner wall surface (14a) of the through-hole (14). The through-hole (14) is divided by the guide plate member (42) into a first passage portion (44) and a second passage portion (46). The first passage portion (44) communicates through a piston groove with a scavenging passage of a cylinder. The fuel discharged from the fuel outlet (30) is guided by the guide plate member (42) to the second passage portion (46) and is supplied through the second passage portion (46) to a fuel-air mixture passage (24) of an engine intake system.

An amount of air taken into an air leading type two-stroke engine is increased to enhance an engine output, and gas emission characteristic deterioration caused by blow-back is inhibited. An inhibition member 16 is disposed between a choke valve 4 in a full open position and a throttle valve 6 in a full open position. The inhibition member 16 includes, for example, a mesh member like a metal mesh. Mixed fuel containing oil is supplied to the air-fuel mixture channel 14. Numerous pores of the inhibition member 16 (mesh member) are occluded by a membrane of oil components of the mixed fuel. Consequently, entry of a blow-back flow of an air-fuel mixture from the air-fuel mixture channel 14 into the air channel 12 through the numerous pores of the flow inhibition member 16 (mesh member) can be inhibited.

An internal combustion engine (1) may include a combustion chamber (41) into which a mixture (40) of fuel and air is supplied, a spark plug (50) disposed proximate to the combustion chamber (41) to ignite the mixture (40) by generating a spark such that ignition of the mixture drives a piston (6) operably coupled to a crank portion (12) of the engine (1), a speed sensor (102) configured to determine engine speed, and an electronic control unit (100) configured to control operation of the spark plug (50). The electronic control unit (100) may be configured to initiate a speed limitation operation in response to engine speed reaching a cut out speed threshold and to control ignition timing within an operating band (320) of ignition angles prior to engine speed reaching the cut out speed threshold. The speed limitation operation may include skipping application of sparks. The electronic control unit (100) is further configured to apply a changed ignition angle (330) relative to the operating band (320) for first at least one spark initiated after the speed limitation operation.

An internal combustion engine (1) may include a combustion chamber (41) into which a mixture (40) of fuel and air is supplied, a spark plug (50) disposed proximate to the combustion chamber (41) to ignite the mixture (40) by generating a spark such that ignition of the mixture drives a piston (6) operably coupled to a crank portion (12) of the engine (1), a speed sensor (102) configured to determine engine speed, and an electronic control unit (100) configured to control operation of the spark plug (50). The electronic control unit (100) may be configured to initiate a speed limitation operation in response to engine speed reaching a cut out speed threshold and to control ignition timing within an operating band (320) of ignition angles prior to engine speed reaching the cut out speed threshold. The speed limitation operation may include skipping application of sparks. The electronic control unit (100) is further configured to apply a changed ignition angle (330) relative to the operating band (320) for first at least one spark initiated after the speed limitation operation.

A two-stroke engine includes a crankcase defining a cylinder bore, a piston moveably disposed within the cylinder bore, and a cylinder head that covers the cylinder bore. A wall surface of the cylinder bore, a piston combustion surface of the piston, and a head combustion surface of the cylinder head, cooperate to define a combustion chamber for combusting a fuel therein. A thermal conductivity reducing mechanism is disposed in thermal connectivity with at least one of the crankcase, the piston, and the cylinder head for reducing heat transfer from combusted fuel within the combustion chamber to at least one of the crankcase, the piston, and the cylinder head. The thermal conductivity reducing mechanism may include a layer of low conductivity material coating one of the surfaces defining the combustion chamber, or a void in the cylinder head and/or the crankcase adjacent the combustion chamber.

A two-stroke engine includes a crankcase defining a cylinder bore, a piston moveably disposed within the cylinder bore, and a cylinder head that covers the cylinder bore. A wall surface of the cylinder bore, a piston combustion surface of the piston, and a head combustion surface of the cylinder head, cooperate to define a combustion chamber for combusting a fuel therein. A thermal conductivity reducing mechanism is disposed in thermal connectivity with at least one of the crankcase, the piston, and the cylinder head for reducing heat transfer from combusted fuel within the combustion chamber to at least one of the crankcase, the piston, and the cylinder head. The thermal conductivity reducing mechanism may include a layer of low conductivity material coating one of the surfaces defining the combustion chamber, or a void in the cylinder head and/or the crankcase adjacent the combustion chamber.

In at least some implementations, an engine control process includes an engine speed test and other steps. The engine speed test includes the steps of a) determining a first engine speed, b) changing the air/fuel ratio of a fuel mixture delivered to the engine, and c) determining a second engine speed after at least some of the air/fuel ratio changing event, Based at least in part on the difference between the first engine speed and the second engine speed it is determined if a change in the air/fuel ratio of the fuel mixture delivered to the engine is needed. If a change to the air/fuel ratio was indicated, the air/fuel ratio of a fuel mixture delivered to the engine is changed.