Cover: Proceedings of the Symposium on Recent Advances in Geotechnical Centrifuge Modeling, National Geotechnical Centrifuge, Department of Civil Engineering, University of California Davis

Introduction: A symposium on Recent Advances in Geotechnical Centrifuge Modeling was held on July 18-20, 1984 at the University of California at Davis. The symposium was sponsored by the National Science Foundation's Geotechnical Engineering Program and the Center for Geotechnical Modeling at the University of California at Davis.

The symposium offered an opportunity for a meeting of the InternationalCommittee on Centrifuges of the International Society for Soil Mechanics and Foundation Engineering. The U.S. participants also met to discuss theadvancement of the centrifuge modeling technique in the U.S. A request is being transmitted to the American Society of Civil Engineers to establish a subcommittee on centrifuges within the Geotechnical Engineering Division.

Editor: Proceedings edited by J. A. Cheney.

This work proposes a new Stirling engine design which we refer to as an actuated Stirling engine. The thermodynamic cycle which drives the engine is controlled by the motion of the displacer piston. In traditional designs this motion is a result the design parameters of the engine. In the Beta engine design the motion of the displacer is determined by the design of the flywheel, while in a free piston design the motion is determined by the restorative force applied to the displacer (be that from a gas spring used in some designs or a mechanical spring used in others). This work proposes a new design wherein the displacer motion is directly controlled via an actuator. This allows for more direct control over the thermodynamic process which drives the engine. To answer the question of how well this engine design compares to a more traditional engine, the best possible design of both engines are compared to one another. This requires optimizing not only the proposed design, but the more traditional design as well.

The traditional Beta engine design is chosen as the benchmark with which the actuated design is compared to. Optimizing the design of the Beta engine is a standard parameter optimization problem, as the motion of the pistons is determined by the flywheel parameters. Optimizing the actuated engine is more difficult as it requires finding the optimal trajectory of the displacer, which is an optimal control problem.

This work is divided into two sections. In the first section the problem of optimally designing both the actuated and Beta engine designs is solved using a very simple of the Stirling engine, the isothermal (or Schmidt) model. In the second section the same design problem is solved but with a much higher fidelity engine model. The large state dimension of the high fidelity model makes it ill suited for use in an optimization algorithm. To resolve this, a method of model reduction is proposed and applied to the high fidelity model to yield a reduced model more suitable for use in an optimization algorithm. For both the simple isothermal and high fidelity models it is shown that the actuated design has the potential to significantly outperform the more traditional Beta engine design.

Engineering is a relevant tool to solve current challenges in a variety of fields. There is a demand for engineers in the workforce and a method to solve that demand is to introduce students to engineering prior to college coursework. One of the ways that students can engage with engineering earlier is through engineering design projects. This research takes place in a high school setting and engages freshmen in an engineering design project. Four groups of student participants were included in the research. The students conducted video recordings, which were analyzed to determine the abilities that students possessed in a design project. Students were given a modified engineering design cycle to provide structure and guidance for their work throughout the project. The engineering design cycle is a method used to solve problems. The final step of the project was for each group to create a video from their video recordings that explained their engineering design process.

Generally, students did not spend a lot of time in the understanding, brainstorming, or planning phases of the design cycle. However, they did spend a lot of time designing and improving their design. The communication that the students exhibited through their videos varied. Two of the groups had effective communication styles and were able to describe their process, while two of the groups were not effective communicators and did not correctly describe their process. The project offered a scholarly contribution to the field of engineering by highlighting engineering for high school students, promoting the use of the engineering design cycle, and demonstrated how students can act like an engineer given an engineering design project.

The internal combustion engine has vastly improved over the past 100 years. With global warming and pollution being a rising concern, engineers are working towards improving efficiency and emissions of engines. The spark-ignited engine (or gasoline engine) offers improvement in emissions with a sacrifice in thermal efficiency. The compression ignition engine (Diesel engine) increases the thermal efficiency, due to operation at higher compression ratios, but emits high amounts of particulate matter and oxides of nitrogen (NOx). Although improvements in fuel refinement have decreased the amount of engine pollutants, the output of pollutants for both spark-ignited and Diesel engines is still too great.

This dissertation explores two advanced engine concepts with alternative fuels for improving thermal efficiency and reducing emissions in automobiles. The first concept investigated is a spark-ignited internal combustion engine operating using hydrogen, oxygen, and argon. Basic engine theory predicts such an engine will see a considerable improvement in engine efficiency (theoretically ~75%, and in practice ~50% including heat transfer and friction losses) over standard engines. These gains in thermal efficiency are due to argon's monatomic structure, which yields a high specific heat ratio (γ = 1.67 compared to γ < 1.4 for air). The water produced by the combustion of hydrogen can be extracted in the exhaust by a condenser, allowing the recycling of nearly pure argon in a closed loop system. Therefore, argon re-fueling is not required.

Achieving efficiencies above 50% with a hydrogen-oxygen-argon engine, however, is difficult due to engine knock limiting spark advance. In an effort to obtain the highest efficiency of this engine concept, experiments were conducted using single and dual spark-ignition for high argon concentrations. Results showed dual spark-ignition slightly increased indicated thermal efficiency, but was still limited by engine-knock. A three-zone model showed that argon as a working fluid increases in-cylinder temperatures, unburned gas temperatures, and laminar flame speed. The model suggests that specific heat ratio affects end gas temperatures more than increasing flame speed.

The second engine concept investigates variables and fuel trends for predicting ignition in homogenous charge compression ignition (HCCI) engines. Octane number, a metric for fuel performance in gasoline engines, and cetane number, a metric for fuel performance in Diesel engines, do not accurately predict fuel performance in HCCI engines. To develop a metric for predicting fuel performance in HCCI engines, correlations between ignition of fuels in an HCCI engine and varying engine parameters are investigated. A relationship between fuel chemistry and ignition in HCCI engines is also explored. Results show that previous methods for predicting ignition do not correlate well with experimental data and auto-ignition is highly sensitive to fuel chemistry.

A single-zone well-mixed-reactor model is used to investigate three different mechanisms for predicting auto-ignition in the HCCI engine. All three mechanisms accurately predicted the auto-ignition order of fuels containing isooctane and n-heptane, but did not predict auto-ignition of blends containing toluene and ethanol. Blends of toluene and n-heptane were further investigated using the model to identify potential problems with the toluene mechanisms. The model results showed increasing the amount of toluene linearly by volume did not result in a linear advance in auto-ignition.