Two stroke cycle engine with sustained power stroke

A two-stroke cycle internal combustion engine has a sustained power stroke which results from delayed mixing of a stratified charge. Use of delayed mixing of an overall stoichiometric air-fuel mixture results in formation of a low amount of the oxides of nitrogen. Delayed mixing of a stratified charge is achieved by placement of a Helmholtz resonator cavity in the piston and peripherally just below the crown thereof. The Helmholtz resonator cavity communicates with the combustion chamber via a narrow slot made by undercutting the top edge of the piston. A port type intake valve is used. Pressurized air passing through the intake port during the exhaust phase of the cycle streams past the undercut top edge of the piston. After the engine cylinder has received a charge of fresh air the compression stroke is begun and the main chamber is filled with a slight fuel-rich gaseous charge. The companion Helmholtz resonator cavity receives only an air charge from the intake port. During the compression stroke some of the fuel-rich mixture is forced into the resonator cavity via the communicating slot. However, even at maximum compression the air-fuel mixture within the cavity remains lean. At or near TDC, the air-fuel mixture in the main chamber is ignited. As the flame front progresses across the chamber, a rapid increase in pressure serves not only to power the piston, but also to initiate a resonant reaction in the Helmholtz resonator cavity. This results in a transfer of the unburned gases therein into the main chamber, thereby sustaining the power stroke over a longer period than would occur when operating on a conventional Otto cycle.