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Middle Tennessee State University
Numerous studies have concentrated on enhancing the efficiency of internal combustion engines through various means, including refined design, superior materials, and regenerative technologies. Toyota recently reported a 40% gasoline engine efficiency with their Prius model in 2016. However, further research is warranted for improvement towards reaching the theoretical value of 73% efficiency as outlined by the Carnot Theorem. The first section of this dissertation gives an in-depth introduction of internal combustion engine from aspects including the history and the popular modern design as well as the history of the inventions of rotary valve engines. In the second section, the concept of using rotary valve instead of the conventional poppet valve for internal combustion engine is proposed. The study lists major drawbacks of the conventional poppet valve and explains the advantages of the rotary valve in general. A novel vertical positioned, servo motor driven, bell shape rotary valve is proposed to potentially improve the efficiency of a known conventional valve designed engine. The data of the new design is compared to the conventional poppet valve design with respect to several parameters to discuss its working principle and advantages over the conventional valve mechanism. Modeling is performed using Python programming to predict the valve opening mechanism. The experimental design is setup to control and tune different parameters accordingly within the reasonable range of engine speed viz. 1000-6000 RPM to simulate various working conditions. The maximum opening area for the rotary valve is calculated to be 0.795 which is smaller than the poppet valve’s area of 1.315 However, under an example of 2900 RPM, the rotary valve was able to remain fully opened with constant efficiency of about 54% from 40 to 160 degrees of the crankshaft angle, while the poppet valve achieves 88% efficiency at 90 degree of the crankshaft angle and the efficiency significantly drops on either side of the maximum. Calculation shows that the proposed rotary valve can gain better performance with engine speed below 4400 RPM which is acceptable for real world use. Building on these findings, the third section develops and improves the rotary valve mechanism and the engine design. With key parameters such as displacement, cylinder bore, stroke, and compression ratio remaining the same, a transvers positioned, servo motor driven, spherical shape rotary valve is introduced. Instead of retrofitting the existing engine head with the bell-shaped valve, a new engine head design is developed, aiming to minimize the overall number of components required. A new spindle port shape is proposed, accompanied by a comparative calculation with the traditional circular shape. The valve flow coefficient prediction and in-cylinder pressure prediction are performed followed by volumetric efficiency prediction. An engine simulation based on the ideal Otto cycle is conducted with adequate predictions and parameter settings. The results reveal that the spherical shape rotary valve achieves a valve opening area comparable to that of the conventional poppet valve. Additionally, the spindle valve opening port shape delivers a volumetric efficiency gain of up to 3% compared to the circular shape at the same crankshaft angle. This improvement in volumetric efficiency is attributed to the engine's kinematics and mechanical engineering principles. The rapid creation of valve opening area by the rotary valve during the intake process results in very low negative work, as depicted in the P-V diagram from the engine simulation. Overall, these findings underscore the potential of the spherical shape rotary valve and spindle valve opening port shape to enhance engine performance and efficiency, offering valuable insights for further advancements in internal combustion engine design.
Mechanical engineering