Appendix 6 on microfiche in end pocket / 256 leaves : ill., diagrs., graphs, photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1978

Appendix 6 on microfiche in end pocket / 256 leaves : ill., diagrs., graphs, photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1978

Thesis (Ph.D.) -- University of Adelaide, Department of Mechanical Engineering , 1978. / Appendix 6 on microfiche in end pocket.

An innovative two-stroke engine has been under development at Queen’s University. Traditional crankcase-scavenged two-stroke engines have laboured to meet emissions standards and achieve fuel economy comparable to four-stroke engines. The engine in question makes use of a modified Eaton-type supercharger to enable air-only scavenging, with this it utilizes direct fuel injection which occurs after the exhaust ports have closed, these two elements combine to eliminate the combustion of lubricating oil in the cylinder and short-circuiting of the fuel-air mixture into the exhaust. By having passive check valves in the cylinder head to regulate the inflow of scavenging air, and exhaust ports located near bottom centre this results in a top-down uniflow-scavenged configuration, as well as retaining a simplistic engine design. In the two-stroke cycle, using the intake charge to replace the combustion products with fresh air during scavenging is critical to engine performance. In this engine the scavenging charge is produced by a set of passive intake check valves, and because of this the scavenging timing is important. These valves are important because they govern the volume of combustion products that are forced out of the cylinder during scavenging, and hence the efficiency of combustion in the engine. To evaluate the engine design criteria, a validated computational fluid dynamic (CFD) model was used to offer insight into how the in-cylinder flow developed during scavenging. The CFD model of this engine was used to test different check-valve geometries to see how they affect the scavenging flow in the cylinder. The goal of this is to assist in entraining more of the combustion products which would result in more being exhausted from the cylinder. A more favourable design was found, and a design produced to be taken onto the next step of testing. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2010-07-12 17:09:58.81

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Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xxvii, 166 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 121-126).

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Despite challenges with poor emissions and fuel economy, gasoline two stroke engines continue to be developed for a number of applications. The primary reasons for the choice of a gasoline two stroke engine includes its low cost, mechanical simplicity and high specific power output. Some applications for the gasoline two stroke engine include small capacity motorcycles and scooters, off road recreational vehicles, hand held power tools and unmanned aerial vehicles. New technologies, which are already mature in four stroke engines, are now being applied to two stroke engines. Such technologies include direct fuel injection, electronic engine management and exhaust gas after treatment. To implement these new technologies computation models are being continuously developed to improve the design process of engines. Multi-dimensional computational fluid dynamics modelling is now commonly applied to engine research and development, it is a powerful tool that can give great insight into the thermofluid working of an engine. Multi-dimensional tools are however computationally expensive and quasi-dimensional modelling methods are often better suited for the analysis of an engine, for example in transient engine simulation. This thesis reports the development of a new quasi-dimensional combustion model for a loop scavenged two stroke engine. The model differs from other quasi-dimensional models available in the literature as it accounts for a bulk motion of the flame front due to the tumble motion created by the loop scavenge process. In this study the tumble motion is modelled as an ellipsoid vortex and the size of the vortex is defined by the combustion chamber height and a limiting elliptical aspect ratio. The limiting aspect ratio has been observed in experimental square piston compression machines and optical engines. The new model also accounts for a wrinkled flame brush thickness and its effects on the interaction between flame front and combustion chamber. The new combustion model has been validated against experimental engine tests in which the flame front propagation was measured using ionization probes. The probes were able determine the flame front shape, the bulk movement of the flame front due to tumble and also the wrinkled flame brush thickness.

It is standard practice in one-dimensional gasdynamic simulations of high performance two-stroke engines to model the exhaust tail pipe entry as an area change using an algorithm similar to the area change of the reverse cone. In the reverse cone the area continually steps down while at the tail pipe entry it changes from stepping down to constant area. At this point a vena contracta can form that effects the flow resistance of the tail pipe. In an effort to improve the accuracy of the gasdynamic simulations the area change algorithm at the tail pipe entry was replaced with a restriction algorithm that incorporates a coefficient of discharge and allows an increase in entropy on the expansion side. The coefficient of discharge is defined as the actual measured mass flow divided by the mass flow predicted by the restriction algorithm. An experimental set up was designed and constructed to measure mass flows for a variety of tail pipe entry geometries at a range of pressures covering the pressure ratios encountered in a real engine. From the mass flow results the coefficients of discharge for a range of pressure and area ratios and reverse cone angles could be calculated and arranged into matrix form to define Cd-maps. The Cd-maps were incorporated into the simulation software and tested to ensure that it functioned correctly. <p<Finally, the simulation results with and without the Cd-maps were compared to measured results and it was shown that incorporating this refinement improves the accuracy of the simulation results on the “over run” part of the power curve. This is the part of the power curve after maximum power and very important in the development of high performance two-stroke engines. These maps can be used for all future simulations on any engine size that uses the same tail pipe geometry. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted