A New Rotary Valve for 2-Stroke Engines Enabling Over-Expansion

摘要

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. This combines the kinematic of the piston with the kinematic of the valve in order to determine the required valve angles to perform the required exhaust timing. With this model the authors were able to obtain the valve parameters for different engine conditions and visualize geometry limitations of the valve for each engine event. For the thermodynamic analysis the authors were able to use the data from the referred kinematic model to create a 3D model of the engine. The 3D model was then implemented using the software CONVERGE CFD which simulated the flow and thermal effect of the valve on the engine behaviour. The simulations were performed for a single engine geometry but with different valve conditions/geometry and different compression ratios. It was concluded that indeed it is possible to effectively implement this kind of valve and achieve the intended over-expansion effect.