Abstract
Statement of Problem: Improvements to internal combustion efficiency have soared in the last decade due to stricter emission regulations and increased consumer demand for fuel-efficient vehicles. Variable valve timing (VVT), engine start-stop cycles, direct injection, and close-coupled catalytic converters are only a few of the technologies now found standard in most new cars now sold. However, this technology has largely been absent from smaller displacement engines typically found in two- and three-wheeled vehicles. This thesis examines the use of a computer-based engine cycle program to simulate the effects of adding VVT technology to a small displacement, high-speed relatively modern motorcycle engine, and whether the output gains, if any, mirror those of the larger engines used in automobiles and light trucks. Sources of Data: The bulk of the raw simulation data was generated by the Lotus Engine Simulation software in the form of text and CSV files. The dissemination of these data forms the basis for the conclusions reached. A portion of the background information was culled from two pivotal textbooks on four-stroke internal combustion engines: John Heywood’s Internal Combustion Engine Fundamentals (2nd Edition), and Gordon P. Blair’s Design and Simulation of Four Stroke Engines. All input data required by the Lotus program was empirically derived from disassembling a Honda 600 F4i engine and performing metrology inspection in line with established CSUS lab practices, using calibrated instruments. Where empirical measurements were not practical, the Honda F4i service manual provided additional information. Conclusions Reached: After validating the software as a reliable source of engine performance data, single and parametric study simulations were performed to gather engine performance characteristics with inlet and exhaust valve parameters that were varied through a set of values that used the OEM fixed values as a center line. Three 2-D parametric studies were performed for 100% throttle, steady state operation: varying intake valve lift + closing time, varying exhaust valve closing time + intake valve opening time (overlap), and finally varying intake valve lift + exhaust valve lift. The results show that at full throttle, the use of VVT improved torque output by an average of 6% throughout the entire engine speed range, and decreased fuel consumption by 1-2 percent. If implemented in a production setting, these gains would come with the drawbacks of increased mass (and complexity) in a system that can hardly afford both, given the already small build envelope of motorbikes, and increased cost to consumers. However, given that motorbikes are currently higher greenhouse gas emitters than passenger cars, it is a small price to pay to at least slow the tide of pollution currently being output by this transportation group.