Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 120-122).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 186-190).

The yields of the reactions 12C(α, α ')12C* to the T=0 state at 12.71 MeV (Jπ=1+ ) and the T=l state at 15.11 MeV (Jπ=1+ ) were measured by detecting the decay of these levels to the ground state by gamma emmission. A 90° (lab) yield curve from threshold to Eα= 27.0 MeV was obtained for each reaction. Both states have to be populated via an unnatural parity process and in addition the population of the 15.11 MeV level is isospin forbidden. Nevertheless, excitation of both levels is unambiguously detected. Although the ratio of the yields has a considerable energy dependence ( 1%<̲δ15.11/ δ 12.71<̲ 20%), conclusive evidence is shown for the breaking of isospin in l60*(Ex = 24.0 to 27.3 MeV). The 15.11 MeV yield curve had considerable structure, suggesting the formation of interimmediate states in 16₀* . While the yield of the 12.71 MeV gamma ray also showed evidence of structure, it was not as . dramatic as the 15.11 MeV gamma ray. The yield of the reaction 10B(a ,dy)12C* to the 12.71 and 15.11 levels was also measured. If the outgoing particle is a true deuteron and not an unbound n-p pair, the population of the i5.ll is isospin forbidden. Contrary to the 15.11 and 12.71 yields in 12C(a , a’)12C*f no resonant structure was found ln either the 12.71 or 15.11 yields; it is suggested that the reactions proceed through an isospin allowed sequence. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Baryons are considered in the Nonrelativistic Quark Model (NQM) to be bound states of three valence quarks. Each quark has two possible spin eigenstates in the restframe of the baryon whose spin is fully carried by quarks. The baryon wavefunctions are connected through SU(6) symmetry rotations. For a long time, the measured magnetic moments of the baryons appeared to be in agreement with the NQM predictions. However, recent experiments which are examining the spin structure of the baryons show the failure of several NQM predictions. The so-called 'spin crisis' arose from the interpretation of the EMC deep inelastic scattering measurement of ∫ g^p₁ that the quark spins in the proton appeared to sum up to (almost) zero. In this thesis it will be demonstrated that the spin problem is not a phenomenon restricted to quasi-massless current quarks in the high energy limit. Symmetry arguments are used to examine the baryon magnetic moments and reveal that we can observe massive but pointhke constituent quarks, with a characteristic mass ratio m_u = m_d ≃ ²andfrasl;₃m_s. Surprisingly they do not contribute much to the baryon spin either. This analysis is free of the ambiguity arising from the UA(1} gluon anomaly which makes it impossible to calculate precisely the spin sum of the current quarks. One important finding in our analysis is the observation that the effects of SU(6) breaking hyperfine spin-spin interactions (which cause well-known splittings in the baryon masses) can be seen in the environment dependence of the constituent quark masses. The effective mass of a quark cannot be independent of its surrounding energy since the mass of the baryon is distributed amongst its constituents. Consistent with the hypothesis that different quark masses do not impose SU(3) breaking on the baryon wavefunctions is the observation of induced 'second class' form factors. The way in which SU(3) breaking alters the ^g_Aandfrasl;_{g_V} ratios in semileptonic hyperon decays will be discussed and strong evidence for a new value of F/D is given, which is close to its SU(6) value. This value is derived independently from the baryon β-decays <strong>and</strong> from their magnetic moments. Dynamical models are discussed which might explain the observed polarised strangeness 'inside' the proton, and the almost vanishing quark spin sum.

The efficiency of an internal combustion engine is highly dependent on the peak pressure at which the engine operates. A new compound engine concept, the double compression expansion engine (DCEE), utilizes a two-stage compression and expansion cycle to reach ultrahigh efficiencies. This engine takes advantage of its high-integrity structure, which is adapted to high pressures, and the peak motored pressure reaches up to 300 bar. However, this makes the use of conventional combustion cycles, such as the Seiliger–Sabathe (mixed) or Otto (isochoric) cycles, not feasible as they involve a further pressure rise due to combustion. This study investigates the concept of isobaric combustion at relatively high peak pressures and compares this concept with traditional diesel combustion cycles in terms of efficiency and emissions. Multiple consecutive injections through a single injector are used for controlling the heat release rate profile to achieve isobaric heat addition. In this study, the intake pressure is varied to enable a comparison between the isobaric cases with different peak pressures, up to 150 bar, and the mixed cycle cases. Tests are performed at several different levels of EGR. The experiments are performed on a 12.8 L displacement 6-cylinder Volvo D13C500 engine utilizing a single cylinder with a standard 17-compression-ratio piston. In this study, the cylinder represents the high-pressure unit of the DCEE. The fuel used in all the experiments is a standard EU diesel. In each target condition, the different injection strategies are compared with the total amount of fuel kept relatively constant. The results prove that the isobaric combustion concept is feasible with a traditional injection system and can achieve gross indicated efficiencies close to or higher than those of a conventional diesel combustion cycle. Moreover, the results show that with an isobaric cycle, heat transfer losses can be reduced by over 20%. However, the exhaust energy is higher, which can eventually be recovered in the second stage of expansion. Thus, this cycle could be suitable for the DCEE concept. The CO, UHC and soot emission levels are proven to be fairly similar to those of the conventional diesel combustion. However, the NOx emissions are significantly lower for the isobaric combustion.

No description available.

Thesis (Ph.D.)--University of California, Berkeley, 1962. / "UC-34 Physics" -t.p. "TID-4500 (17th Ed.)" -t.p. Includes bibliographical references (p. 67-69).

Abstract: This thesis aims to contribute to the development of the isobaric combustion engines by exploring multiple injection strategies, by means of computational simulations using a commercial software Converge. A single injection case validated with experimental data in terms pressure trace and heat release rate was used as a baseline reference. The adjustment of the turbulent kinetic energy dissipation constant is found to have the most significant influence in reproducing the pressure and heat release rate histories observed in the experiment. As a first attempt to achieve isobaric combustion, a multiple injection strategy using a single injector was explored with up to four consecutive injections. Considering that the computational simulations were unable to reproduce the experimental data due to a number of uncertainties in the implemented models, the present study attempted to identify the main causes of the discrepancies through various parametric studies. First, different liquid fuel properties were examined and it was found that, while the physical properties of the fuels have a notable effect in terms of evaporation and atomization, such variations were not sufficient to reproduce the experimentally observed heat release cycle. Next, the effects of the uncertainties in the kinetic mechanisms were assessed by the reaction multiplier, an artificial adjustment of the rate constants, and it was found that the reaction multiplier affected the ignition of the first injection, but not the subsequent injection events. As such, the use of reaction multipliers to reproduce the experimental data was found to be unsuccessful. The effect of thermodynamics properties was also examined by employing real-gas equations of state, such as Redlich-Kwong and Peng-Robinson, and the results showed little difference at the conditions under consideration. Finally, advancing the start of injection was found to have the most significant effect on pressure trace and heat release rate to lead to a substantial improvement in the numerical prediction. The results suggest that the key uncertainties in modeling of the present engine combustion are likely the accurate timing of the start of injection combined with the exact injection rate shape profile.

There is an urgent call for action to address the energy efficiency, climate, and local air quality concerns associated with transport because of CO2, particulates, nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) emissions. This has driven the international policy agenda towards reducing greenhouse gas (GHG) with a major emphasis on CO2 emission. Fossil fuel combustion is considered a main contributor to the emission of CO2. The transport sector with a particular emphasis on ground transport is considered the fastest growing sector among all emission sources. To meet climate change goals, governments around the world may need to implement strict regulations on the transport sector. Governments around the world have indeed set stricter emissions standards for vehicles as a way to reduce greenhouse gas emissions from the transport sector. These standards can be achieved through various methods, such as requiring more efficient engines, alternative fuels, or the adoption of electric vehicles. On the other hand, in recent years, a lot of effort was put into promotion of electric vehicles as zero emissions vehicles. This statement should be reconsidered, since the greenhouse impact of electrical vehicles is not negligible. Conversely, in some cases, an electrical vehicle can have an even higher emission impact than modern vehicles with sophisticated internal combustion engines. In fact, the pollutant emissions discharged at the tailpipe outlet will be so low as to be hardly measurable, and their practical impact on air quality will be negligible. In terms of particulate matter emission for example, the impact of tire and brake wearing is already much higher than that due to the ICE (tire wear produces around 50 mg/km of particulates), reaching values around 10 times the emission from the engine (5 mg/km). This implies that today’s conventional ICE-powered-car is equivalent to fully electric and hybrid cars with regard to particulate emissions, when tire and brake and other contributions (e.g. road dust) are accounted for. All the data indicate that ICEs will never cease to exist and the majority of cars will be powered by ICEs in the future. These factors sparked my work on the simulation of ICEs. The first project was mainly focused on high-pressure isobaric combustion, which is a promising concept that has the potential to introduce high efficiency. This work started with the development and validation of the computational models for full cycle combustion engine simulations to capture the flow and combustion characteristics and their interactions with the intake and exhaust flows through the valves and ports. The computational models were extensively validated against the optical engine experiment data, to ensure the fidelity needed for predictive simulations. Upon identifying the numerical models, a comparative study of isobaric and conventional diesel combustion was conducted. The results revealed the superiority of the isobaric combustion mode compared to the conventional diesel combustion especially at high load conditions. On the other hand, the isobaric combustion led to high soot levels compared to the conventional diesel combustion due to the undesirable spray-to-spray interactions resulting from a single central injector with multiple consecutive injections which introduced a fuel-rich zones. For the same injection technique, a study of the effect of injection pressure and the number of holes were numerically investigated as means to reduce the soot levels. To further decrease the soot emissions, multiple injector configurations were used and the results showed more than 50% drop in the soot levels and an increase in the indicated thermal efficiency due to the lower heat transfer losses. The successful injection strategies for low-emission isobaric combustion mode have further motivated research about fuel flexibility. The potential of using fuels from different sources with varying reactivity was explored by utilizing the high pressure combustion. Various primary reference fuels (PRFs) were employed at the same middle engine load, varying from PRF0 up to PRF100. Different injection methods from a single to four injections were studied. The results demonstrated that various PRFs showed significant discrepancies when using a single injection method, owing to the different fuel auto-ignition capability. On the other hand, excellent fuel flexibility was achieved by employing a small pilot injection, under this condition various fuels led to similar engine combustion performance and emissions. Exhaust gas recirculation (EGR) was used as a way to reduce NOx emissions where 50% EGR was employed. To reduce soot emissions, various volume fractions of three shorter-chain alcohols (methanol, ethanol, and n-butanol) were blended with the baseline fuel (n-heptane). The methanol-blended fuels yielded the lowest soot emissions, but the worst fuel economy was obtained due to the highest heat transfer losses. By increasing the nozzle number and introducing an adequate amount of isochoric combustion, the fuel economy for pure methanol combustion was effectively promoted. The second project was focused on ultra-lean hydrogen combustion using CONVERGE CFD as computational framework. The problem of numerically detecting engine knock and the methods to mitigate such a problem were addressed. Different combustion modes such as port fuel injection spark ignition (PFI SI), homogenous charge compression ignition (HCCI), and pre-chamber (PC) were investigated. The effects of the chemical mechanisms in terms of ignition delay time and laminar flame speed were studied. Starting with the simple combustion mode using PFI SI, high engine knock tendency was observed. The effects of compression ratio, air-fuel-ratio, and spark time were examined as means to reduce engine knock. Upon mitigating the engine knock issue, a comparative study of the PFI spark ignition and the PC modes was conducted. The results revealed that the current used design of the PC introduced high turbulence levels, which resulted in high heat transfer losses to the engine piston. In general , all of these studies (isobaric and hydrogen combustion) were aimed to increase the overall engine efficiency and reduce the emissions.