The development of a numerical model of a two-stroke engine is undertaken to study the scavenging characteristics of the engine. The engine design is unique in its use of 16 passive intake valves in the cylinder head which, along with the exhaust ports located at bottom centre (BC), give the engine a top-down uniflow-scavenged configuration. Each valve constitutes a small stainless steel platelet within a cavity in the cylinder head which reacts to the pressure difference across the cylinder head. The principle focus of this study is the transient simulation of the scavenging flow using dynamic meshing to model the piston motion and the response of the passive intake valves to the scavenging flow for varied engine speed and peak pressure. A flowbench study of the steady flow through the cylinder head into a duct is incorporated as a step in the development of the transient numerical model. Validation of the numerical predictions is undertaken by comparing results from an experimental flowbench for the steady case and using a cold-flow scavenging rig for the transient simulations. Both the steady flow through the cylinder head and the unsteady flow within the cylinder indicate the presence of a recirculation region on the cylinder axis. As a result, short-circuiting of scavenging gas becomes considerable and leads to scavenging characteristics comparable to Hopkinson’s perfect mixing one-dimensional scavenging model. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-09-26 18:38:53.375

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Pollution and environmental concerns require further improvements in engine technologyas well as research of alternative fuels. Users of handheld products are directlyexposed to the exhaust gas and thus to the occurring emissions, which cancause significant damage. Pursuing to reduce emissions is therefore a vital task.The European commission proposed a renewable energy directive, that claims abiofuel share of at least 6,8% by 2030 and a reduction of first generation fuel butan increasing of second generation fuels. Ethanol is up to now the most commonsource of renewable alternatives in gasoline blends. Isobutanol has several advantagesover ethanol and can be produced as a second generation biofuel.This thesis aims to get a better understanding on how isobutanol influences theemission and combustion in small two-stroke engines and furthermore what effectdifferent isobutanol blends with neat gasoline and alkylate have on the engine performance.Different isobutanol blends with neat gasoline as well as alkylate fuel have beenused and analyzed.This thesis has via an experimental study shown, that hydrocarbon as well as carbonmonoxide emission increased with increasing isobutanol percentage. Hence, nitrogenoxides emission decreased with isobutanol. Lower cylinder and exhaust temperatureswere measured with isobutanol blends. Through cylinder pressure measurements,the mass fraction burned, mass fraction burned 50% and rapid burningangle could be analyzed. It has shown that isobutanol blends reach a mass fractionburned of 50% slightly later and have a greater rapid burning angle.

Master of Science / Department of Mechanical and Nuclear Engineering / Kirby S. Chapman / The United States Environmental Protection Agency (EPA) continues to tighten pollutant emission regulations throughout the United States. As a result, the need to reduce air pollutants such as nitrogen oxides (NO[subscript]x) and carbon monoxide (CO) remains a challenge for pipeline operators. NO[subscript]x formation is primarily a function of in-cylinder combustion temperatures. A challenge for engine researchers is to identify methods to lower combustion temperatures while maintaining complete combustion. Blending hydrogen into an engine's fuel can lower in-cylinder combustion temperatures and reduce pollutant emissions. Hydrogen has a wider flammability range in comparison to natural gas, which allows for leaner engine operation and lower combustion temperatures. Specifically, the very high molecular diffusivity of hydrogen creates a more uniform mixture of fuel and air. Hydrogen also has very low ignition energy, which translates into easier combustion. This paper presents test results of using hydrogen as a fuel additive for a large bore, two stroke cycle, single cylinder, natural gas fueled Ajax engine in a test laboratory. The engine was first operated at the test point on pure natural gas and allowed to stabilize. Then a mixture of hydrogen and natural gas at various molar percentages was introduced. The engine was operated entirely on the blended fuel without a pre-combustion chamber first. Next, a pre-combustion chamber was installed and the blended fuel was supplied to it while the main combustion chamber operated on pure natural gas. Engine and emissions data were recorded and physical observations were also noted, such as engine misfires. Results showed that the addition of hydrogen into the fuel gas without the use of a pre-combustion chamber reduced emissions. The addition of the pre-combustion chamber reduced NO[subscript]x emissions without the use of hydrogen. For both configurations, the engine ran smoother with no noticeable increase in misfires or detonation. The pollutant emission reduction and engine combustion stability suggest that hydrogen as a fuel additive would be a good method to meet emissions requirements.

For any crankcase scavenged two-stroke engine, the fuel dynamics is not easily predicted. This is due to the fact that the fuel has to pass the crankcase volume before it enters the combustion chamber. This thesis is about the development of a model for fuel dynamics in the crankcase of a small crankcase scavenged two-stroke engine that gives realistic dynamic behavior. The crankcase model developed in this thesis has two parts. One part is a model for wall wetting and the other part is a model for concentration of evaporated fuel in the crankcase. Wall wetting is a phenomenon where fuel is accumulated in fuel films on the crankcase walls. The wall wetting model has two parameters that have to be tuned. One is for the fraction of fuel from the carburetor that is not directly evaporated and one parameter is for the evaporation time of the fuel film. The thesis treats tuning of these parameters by running the model with input data from measurements. Since not all input data are possible to measure, models for these inputs are also needed. Hence, development of simple models for air flows, fuel flow, gas mixing in the exhaust and the behavior of the λ-probe used for measurements are also treated in this thesis. The parameter estimation for the crankcase model made in this thesis results in parameters that corresponds to constant fraction of fuel from the carburetor that evaporates directly and a wall wetting evaporation rate that increases with increasing engine speed. The parameter estimation is made with measurements at normal operation and three specific engine speeds. The validity of the model is limited to these speeds and does not apply during engine heat-up. The model is run and compared to validation data at some different operation conditions. The model predicts dynamic behavior well, but has a bias in terms of mean level of the output λ. Since this mean value depends on the relation between input air and fuel flow, this bias is probably an effect of inaccuracy in the simple models developed for these flows. / För alla tvåtaktsmotorer med bränslematning genom vevhuset är bränsledynamiken svårpredikterad. Detta beror på att bränslet måste passera vevhusvolymen innan det når förbränningskammaren. Denna uppsats handlar om utveckling av en modell som ger realistisk dynamik för bränslet i tvåtaktsmotorers vevhus. Vevhusmodellen i denna uppsats har två delar. Den ena delen är en modell för bränslefilm på motorväggar och den andra delen är en modell för koncentration av förångat bränsle i vevhusvolymen. Bränslefilmsmodellen har två parametrar som måste trimmas. Den ena är andelen bränsle från förgasaren som inte förångas direkt och den andra är tidsåtgången för förångning av bränslefilmen. Uppsatsen behandlar trimning av dessa parametrar genom körning av modellen med indata från mätningar. Eftersom inte all indata kan mätas behövs även modeller för dessa. Därför behandlar uppsatsen även utveckling av enkla modeller för luftflöde, bränsleflöde, gasblandning i avgasvolymen och beteende hos den för mätningar använda λ-sonden. Parameterestimeringen för vevhusmodellen som är gjord i denna uppsats resulterar i parametrar som svarar mot konstant andel av bränslet från förgasaren som förångas direkt och en förångningshastighet för bränslefilmen som ökar med ökande motorhastighet. Parameterestimeringen är gjord med mätdata från normal körning vid tre olika motorhastigheter. Giltigheten för modellen är begränsad till dessa hastigheter och kan inte appliceras på körning av motorn vid kallstart. Modellen är körd och jämförd med valideringsdata från olika körfall. Modellen förutser dynamiska beteenden väl, men har ett systematiskt fel gällande medelvärdet på λ. Eftersom detta medelvärde beror på förhållandet mellan luftflöde och bränsleflöde in i vevhuset är sannolikt detta systematiska fel en effekt av osäkerhet i de enkla modeller som utvecklats för dessa flöden.

Engine knock has long been a well recognized phenomenon in the automotive industry. Detecting engine knock opens up the possibility for an indirect feedback of the engine's internal combustion without installing a pressure transducer inside the cylinder. Knock detection has mainly been used for spark advance control, making it possible to control the engine close to its knock limit in search for the optimal ignition timing. This application has to a lesser extent been applied to lightweight two-stroke engines, which is the focus of this study. The investigation features a modern chainsaw engine whose knock characteristics were first determined with a pressure transducer. The structural vibrations originating from the engine knock are filtered out of the signal from a remote located accelerometer. The knock intensity is compared with the signal from the pressure transducer which shows a correlation with an accepted extent between the two sensors. Parameters that affect the knock intensity have also been investigated. These include engine temperature, different types of fuel and ignition timings.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains ix, 64 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 42-43).

This thesis is a study conducted in collaboration with the engine performance group atHusqvarna AB. The study focuses on engine stability of smaller two stroke handheld enginesrunning on E10 (10% ethanol mixture in gasoline). The reason for the study is the new EUproposition that by 2020 all fuel must have 10 % renewable fuel content. To meet thisproposition Husqvarna has evaluated E10 and found that the engine stability of smaller twostroke engines are affected in a negative way by the fuel.The study focuses on events occurring prior to the combustion and mainly the carburetor. Theobjective for the thesis is to seek what contribution the events occurring prior to thecombustion have to the engine stability and find simple and implantable solution to improvethe stability with regards to the carburetor.The study has been conducted in three different work packages, system understanding to buildknowledge of how the carburetor operates, fault finding to seek potential attributes that canaffect the stability and fault mode analysis to seek why the attributes affect the stability.Furthermore, all the attributes found has been tested and validated on the engine to seek theircontribution to the stability.The conclusion made of the thesis is that with simple and implementable improvements of thecarburetor the engine stability could be increased with 40 %. A total of five differentattributes were found to affect the stability of the engine. Furthermore, a very detailedexplanation of how the carburetor operates and components inside the carburetor has beenestablished during the thesis.

<p>Two-stroke, opposed piston engines have gained recent attention for their improved thermal efficiency relative to the conventional inline or V-configuration. One advantage of two-stroke, opposed piston engines is a reduction in heat losses since there is no cylinder head. Another advantage is improved gas exchange via uniflow scavenging since the exhaust and intake ports may be located near bottom dead center of the exhaust and intake pistons, respectively. One challenge with the design of two-stroke engines is promoting turbulence within the cylinder. Turbulence is important for mixing air and fuel in the cylinder and for increasing flame speed during combustion. </p> <p>This work investigates the flow and turbulence through two-stroke, opposed piston engines using computational fluid dynamics (CFD). Specifically, the role of intake manifold and intake port geometry on turbulence within the cylinder was investigated by systematically modifying the engine geometry. Turbulence was then quantified using three metrics: circulation around the cylinder axis (swirl), circulation normal to the cylinder axis (tumble), and volume average turbulent kinetic energy (TKE) within the cylinder.</p> Increasing the swirl angle from 0 degrees to 10 degrees increased the in-cylinder swirl by a factor of 3. Increasing the swirl angle also increased the volume average TKE by a range of 7.6% to 36.5% across the three cylinders of the engine. A reverse tilt angle of 15 degrees increased tumble circulation near the piston face but decreased tumble circulation by a factor of 3 near the center of the cylinder. The next step for research on this would be to apply more geometric manipulations to the manifold of the swirl engine design to balance the mass flow rate for each port. Following the redesign of the manifold the next step is to perform a dynamic CFD test to verify the mass flow has been balanced under a dynamic scenario.

This diploma thesis deals with the design of a two-stroke engine for paragliding. First of all, the different types and designs of two-stroke engines are discussed. After the design of the crank mechanism, the forces in the engine are tested, followed by the strength control of selected components. In addition, the work includes design of individual engine components, propeller reducer and 3D models of components and motor unit.