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One way to increase efficiency and performance of 2-stroke engines is the addition of an exhaust valve to control the opening/closure of the exhaust port. With this implementation it is possible to change the exhaust timing for different conditions. However, conventional systems cannot change the exhaust opening and closure timings independently. The work herein presented shows the development of a new exhaust rotary valve enabling the control of the opening independently from the control of the closure of the exhaust port. The study is based on kinetic and thermodynamic analysis. Some manufacturers use exhaust rotary valves but none of them performs a fully rotary motion. This kind of motion has various benefits such as smoothness and most notably the ability to control both the opening and the closure timing of the exhaust independently. Regarding the kinematic analysis, a simple model was created to determine the most suitable valve angles.

The current study introduces a Variable Valve Timing (VVT) trapezoidal rotary valve for a 4-stroke spark-ignition engine. Being trapezoidal, enables the rotary valve to change the inlet and exhaust timing continuously, therefore allowing it to control the engine load without the need for a throttle valve. The geometry of the valve is studied in detail, calculating the intersection areas between the windows (ports) of the valve and those of the combustion chamber during the engine cycle. As the valve openings are trapezoidal and the opening of the combustion chamber is trapezoidal as well, there is a multitude of geometry variables that need to be optimized. During idle the engine needs to breathe through just a very small area, while during high load operation the opening needs to be generous. Finally, the trapezoidal rotary valve system is compared to a conventional VVT system.