Stratified-charge two-stroke cycle engine
DESCRIPTION 
     1. Technical Field 
     The invention relates to a stratified-charge two-stroke cycle scavenged spark-ignition engine. One application is marine propulsion systems. 
     2. Background 
     In two-stroke cycle engines, it is desirable to scavenge the combustion chamber during the downward stroke of the piston and expel combustion gas with minimal loss of unburned fuel-air mixture admitted for the next cycle. One way of enhancing scavenging is to provide an auxiliary air port in the cylinder to supply scavenging air during the downstroke of the piston. 
     DISCLOSURE OF THE INVENTION 
     A two-stroke cycle engine of reduced fuel consumption is provided, well suited to low cost, low horsepower engine applications, particularly those implementations requiring narrow engine design. An elongated scavenging air passage between the crankcase and the combustion chamber has a length great enough to reduce fuel mixture therein. Fuel is supplied to the crankcase, and a substantially shorter fuel-air transfer passage extends between the crankcase and the combustion chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic partial sectional view of a two-stoke cycle engine constructed in accordance with the invention. 
     FIG. 2 is a cross sectional view taken along line 2--2 of FIG. 1. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A stratified-charged two-stroke cycle scavenged spark-ignition engine 1, includes a piston 2 reciprocal in a cylinder 3 between a combustion chamber 4 and a crankcase 5. A supply system 6 is provided for supplying fuel into crankcase 5. A fuel-air transfer passage 7 extends between crankcase 5 and a fuel-air inlet port 8 in combustion chamber 4. During the upstroke of piston 2, the fuel-air mixture is compressed in chamber 4, and upon ignition of spark plug 9 combustion of the mixture drives piston 2 downwardly to rotate crankshaft 10 through connecting rod 12. The combustion products exit through port 13. 
     An elongated scavenging air passage 14 has an input 15 for receiving external air. Elongated air passage 14 extends between crankcase 5 and an air inlet port 16 in combustion chamber 4. Fuel-air inlet port 8 is approximately 180° opposite exhaust port 13. The air inlet port 16 is located between the exhaust port 13 and the fuel-air inlet port 8. The greater the length of passage 14 between crankcase 5 and combustion chamber 4 the lesser the amount of fuel and the greater the amount of air at port 16. There is thus a reduction in the amount of unburned fuel mixture from port 16 otherwise lost to exhaustion, and furthermore, there is increased substitution of air to reduce the amount of unburned fuel mixture from port 8 otherwise lost to exhaustion. Fuel consumption is reduced by substantially reducing exhaustion of unburned fuel mixture. Passage 14 has a length great enough to reduce fuel mixture therein and afford substantially only air at air inlet port 16 to substitute air for exhaustion at exhaust port 13 instead of otherwise exhausted unburned fuel-air mixture from inlet port 8. 
     The fuel supply system 6 includes carburetor 17, having a butterfly valve 18 and a one-way reed valve 19, mounted to crankcase 5 substantially coaxially with piston 2 to enable a narrow engine design. By supplying the fuel into the crankcase, there is better mixing of fuel and air because the fuel goes into a hot crankcase and is stirred up by the crankshaft and connecting rods to provide better atomization and vaporization. Furthermore, no lubrication pump is required because the carburetor is mounted on the crankcase and supplies the fuel-oil mixture. 
     Air passage input port 15 may be provided by a throttle body, including butterfly valve 20 and one-way reed valve 21, which throttle body is shorter than a carburetor otherwise mounted on side transfer passage 7 and can be mounted closer to the engine since there is no carburetor spit back of fuel. 
     Elongated air passage 14 has a length between crankcase 5 at input port 22 and air inlet port 16 substantially greater than that of fuel-air passage 7. Passage 7 extends from crankcase 5 at a port 23 adjacent piston 2 and has a length approximately equal to the height of piston 2, whereas elongated air passage 14 has a length substantially greater than the height of piston 2. Passage 14 extends from crankcase 5 at a point 22 distally removed from the piston, and has a length preferably at least 1.5 times greater than the height of the piston.