A Composite Two Stroke Cycle as a Platform for Developing a New Class of Two-Stroke Internal Combustion Engines

An overexpanded two-stroke cycle serves as a platform for developing a new class of two-stroke engines capable of achieving both low emissions and increased fuel efficiency. The combustion process and expansion process occur simultaneously at the beginning of a down stroke. By coordinating the rate of fuel injection with the expansion of the working fluid, the combustion process can be designed to operate in a (i) constant volume, (ii) constant pressure, (iii) constant temperature, or (iv) a combination of combustion modes. At the end of a combustion process, the expansion process continues until reaching a relatively low exhaust temperature, resulting in larger expansion ratio than compression ratio. The difference in expansion and compression stroke lengths is utilized to replace cylinder exhaust gas with fresh charge. Air cycle analyses indicates that utilizing the new two-stroke cycle the same power of a four-stroke diesel engine can be achieved with a downsizing ranging from 30-40%.