Investigation of the effect of inlet valve timing on the gas exchange process in high-speed engines
The motivation for this investigation is the potential for the application of Variable Valve Actuation (VVA) technology in high-speed and high power to volume density, four stroke, spark ignition, internal combustion engines. The benefits of this technology have already been proven in medium-speed automotive engines. In the beginning of this thesis the differences between high-speed and medium-speed engines are outlined and a case is presented why this investigation is required. During the preliminary study VVA technology was reviewed and classification was created based on system functionality. Valvetrain and camdrive dynamic considerations were used to identify VVA technologies, which will allow high-speed operation. The main aspect of this investigation focuses on the effect of individual valve events on the gas exchange process of a high-speed engine. If the optimum valve events in terms of engine output for different engine speedsc an be defined, this will allow assessmenot f the potential of selected VVA systems. To accomplish this, a parametric study exploring the sensitivity of charging efficiency to variation of the individual inlet valve events was performed. Results for five different Inlet Valve Opening (IVO) and Inlet Valve Closing (IVC) points are presented. The study employed engine simulation, which was fully validated experimentally. The use of simulation allows not only the study of the effects of valve events on engine performance but also allows explanation of the results by examining the cylinder filling mechanisms and the gas dynamic processes in the inlet and exhaust system. A control strategy was created for each of the selected VVA systems so that it best satisfies the optimum valve events. An assessment and comparison of their potential for improving engine perfonnance was possible.