End-gas autoignition propensity and flame propagation rate measurements in laser-ignited rapid compression machine experiments

2019 Summer.Includes bibliographical references.Knock in spark-ignited (SI) engines is initiated by autoignition and detonation in the unburned gases upstream of spark-ignited, propagating, turbulent premixed flames. Knock propensity of fuel/air mixtures is typically quantified using research octane number (RON), motor octane number (MON), or methane number (MN; for gaseous fuels), which are measured using single-cylinder, variable compression ratio engines. In this study, knock propensity of SI fuels was quantified via observations of end-gas autoignition (EGAI) in unburned gases upstream of laser-ignited, premixed flames at elevated pressures and temperatures in a rapid compression machine. Stoichiometric primary reference fuel (PRF; n-heptane/isooctane) blends of varying reactivity (50 ≤ PRF ≤ 100) were ignited using an Nd:YAG laser over a range of temperatures and pressures, all in excess of 545 K and 16.1 bar. Laser-ignition produced outwardly-propagating premixed flames. High-speed pressure measurements and schlieren images indicated the presence of EGAI. The fraction of the total heat release attributed to EGAI (i.e., EGAI fraction) varied strongly with fuel reactivity (i.e., octane number) and the time-integrated temperature in the end-gas prior to ignition. Flame propagation rates, which were measured using schlieren images, did not vary strongly with octane number but were affected by turbulence caused by variation in piston timing. Under conditions of low turbulence, measured flame propagation rates agreed with the theoretical premixed laminar flame speeds quantified by 1-D calculations performed at the same conditions. Experiments were compared to a three-dimensional CONVERGE™ model with reduced chemical kinetics. Model results accurately captured the measured flame propagation rates, as well as the variation in EGAI fraction with fuel reactivity and time-integrated end-gas temperature. Model results also revealed low-temperature heat release and hydrogen peroxide formation in the end-gas upstream of the propagating laminar flame, which increased the temperature and degree of chain branching in the end-gas and ultimately led to EGAI

Verification and synthesis of asynchronous control circuits using petri net unfoldings

PhD ThesisDesign of asynchronous control circuits has traditionally been associated with application of formal methods. Event-based models, such as Petri nets, provide a compact and easy to understand way of specifying asynchronous behaviour. However, analysis of their behavioural properties is often hindered by the problem of exponential growth of reachable state space. This work proposes a new method for analysis of asynchronous circuit models based on Petri nets. The new approach is called PN-unfolding segment. It extends and improves existing Petri nets unfolding approaches. In addition, this thesis proposes a new analysis technique for Signal Transition Graphs along with an efficient verification technique which is also based on the Petri net unfolding. The former is called Full State Graph, the latter - STG-unfolding segment. The boolean logic synthesis is an integral part of the asynchronous circuit design process. In many cases, even if the verification of an asynchronous circuit specification has been performed successfully, it is impossible to obtain its implementation using existing methods because they are based on the reachability analysis. A new approach is proposed here for automated synthesis of speed-independent circuits based on the STG-unfolding segment constructed during the verification of the circuit's specification. Finally, this work presents experimental results showing the need for the new Petri net unfolding techniques and confirming the advantages of application of partial order approach to analysis, verification and synthesis of asynchronous circuits.The Research Committee, Newcastle University: Overseas Research Studentship Award

Hardware Development and Error Characterisation for the AFIT RAIL SAR System

This research is focussed on updating the Air Force Institute of Technology (AFIT) Radar Instrumentation Lab (RAIL) Synthetic Aperture Radar (SAR) experimental system. Firstly, this research assesses current hardware limitations and updates the system configuration and methodology to enable collections from a receiver in motion. Secondly, orthogonal frequency-division multiplexing (OFDM) signals are used to form (SAR) images in multiple experimental and simulation configurations. This research analyses, characterises and attempts compensation of relevant SAR image error sources, such as Doppler shift or motion measurement errors (MMEs). Error characterisation is conducted using theoretical, simulated and experimental methods. Final experimental results are presented to verify performance of the updated SAR collection system and show improvements to the final product through an updated methodology and various signal processing techniques

Real Option Valuation of a Portfolio of Oil Projects

Various methodologies exist for valuing companies and their projects. We address the problem of valuing a portfolio of projects within companies that have infrequent, large and volatile cash flows. Examples of this type of company exist in oil exploration and development and we will use this example to illustrate our analysis throughout the thesis. The theoretical interest in this problem lies in modeling the sources of risk in the projects and their different interactions within each project. Initially we look at the advantages of real options analysis and compare this approach with more traditional valuation methods, highlighting strengths and weaknesses ofeach approach in the light ofthe thesis problem. We give the background to the stages in an oil exploration and development project and identify the main common sources of risk, for example commodity prices. We discuss the appropriate representation for oil prices; in short, do oil prices behave more like equities or more like interest rates? The appropriate representation is used to model oil price as a source ofrisk. A real option valuation model based on market uncertainty (in the form of oil price risk) and geological uncertainty (reserve volume uncertainty) is presented and tested for two different oil projects. Finally, a methodology to measure the inter-relationship between oil price and other sources of risk such as interest rates is proposed using copula methods.Imperial Users onl

Are all energy resources created equal? a comparative analysis of the dynamics of resources for the energy system

There is a longstanding debate about the future availability of energy resources, and a significant literature has developed around the issues of oil availability in particular. More recently, the availability of lesser-known critical metals, such as lithium and indium, has been called into question. These metals are key components in low-carbon energy technologies and a new evidence base that questions their future availability is emerging. Much of this research applies methods and techniques also applied to the analysis of oil resources, with the implicit assumption that these resources are in some way analogous. However, although there are similarities, there are also structural differences and the appropriateness of the assumed analogy has not been sufficiently tested. This thesis explores the similarities and differences in the structure of the oil, lithium and indium resource systems, examining the likely response of these systems to availability constraints and testing the appropriateness of this assumed analogy. The systems that define the market for resources are dynamically complex and involve a number of different interlinked variables. The way in which these resource systems respond to changes in surrounding conditions arises from the structure of these variables and their linkages. However, much of the existing analysis of critical metals relies on simplistic assumptions regarding the structure and function of these systems. To address this knowledge gap, this thesis first presents case studies of the three resource systems. The case studies are then used to develop three system dynamics models. This thesis finds that, while there are many similarities in the structure of the three resource systems modelled, the differences between them have a significant impact on their dynamic system behaviour. Analysis which overlooks these differences is likely to draw inaccurate conclusions. In particular, the resilience of metals to periods of constrained availability is potentially greater than that of oil if metal recycling is taken into account. However, metals recovered as by-products are potentially limited in their ability to resist constrained availability.Open Acces

Performance Analysis of a Cooperative Search Algorithm for Multiple Unmanned Aerial Vehicles under Limited Communication Conditions

This research investigates the impacts of realistic wireless communications upon a group of unmanned aerial vehicles (UAVs) utilizing a distributed search algorithm. The UAVs are used to survey an area for mobile targets and they require communication to cooperatively locate the targets. The mobile targets do not continually radiate energy, which exacerbates the search effort; a UAV could fly directly over a target and not detect it. A simulation of cooperative UAVs is implemented using the OPNET Modeler network simulation tool. The search performance of a group of UAVs is observed when communication range, data rate, and the number of UAVs are varied. The performance is evaluated based on the total time it takes for the UAVs to completely detect all the targets in a given search area, the number of times internal areas are scanned, the amount of communication throughput achieved, the network traffic generated, network latency, and number of network collisions. The results indicate that the number of UAVs was found to have the greatest impact on the group\u27s ability to search an area, implying that the data shared between the UAVs provides little benefit to the search algorithm. In addition, it was found that a network with a 100 Kbps or faster data rate should allow for minimal congestion and a large degree of scalability. The findings demonstrate that the proposed four-stage search algorithm should operate reasonably well under realistic conditions

Structure and dynamics in framework materials

This thesis details a study of framework materials of the AM2O8 and AM2O7 families, which are of interest due to their unusual thermal expansion properties, phase transitions and often complex structures. The combination of results from NMR and diffraction techniques has enabled several new insights into the structure and dynamics to be made. Chapter 1 reviews the literature on negative thermal expansion materials that are of relevance to this project. Chapter 2 outlines the background to the key experimental techniques employed in this work. Chapter 3 outlines 17O isotopic enrichment techniques and qualitative results for several AM2O8 phases. 17O NMR results for cubic ZrW2O8 including variable temperature spectra and 2DExchange Spectroscopy (EXSY) are presented. The a / ß phase transition and low temperature oxygen mobility in ZrW2O8 are investigated. NMR results enabled the determination of a mechanism of oxygen exchange different to the previously suggested mechanism, which is disproved. The results of in situ diffraction experiments to investigate phase transitions inZrMo2O8 are also presented. 17O enriched samples of cubic-, trigonal- and LT- ZrMo2O8 samples were prepared, and their 17O NMR spectra recorded. Chapter 4 describes quantitative 17O NMR studies used to characterise oxygen dynamics inZrW2O8. The results of a range of NMR experiments, including a combination of 1D EXSY and saturation recovery experiments, are interpreted to give a measure of the rate and the activation energy for oxygen exchange. The experiments and derivation of the required theoretical background are detailed. Chapter 5 outlines a range of structural studies on AM2O7 materials. The room temperature superstructure of HfP2O7 is determined using a combination of X-Ray and neutron diffraction.31P NMR is reported for the high temperature phases of HfP2O7 and ZrP2O7 for the first time. The symmetry of the high temperature phase of HfP2O7 is investigated by Rietveld refinement of neutron diffraction data. Unusual effects in the 51V NMR spectra of HfV2O7 and ZrV2O7 are also reported. Chapter 6 outlines preliminary work on computational methods to investigate the structural dependence of the 31P NMR chemical shift of pyrophosphate materials. DFT calculations of NMR parameters were carried out, and a methodology developed for the derivation of suitable theoretical model structures

Refining the U.S. Navy Flight Clearance (Airworthiness Certification) Process: Maximizing Acquisition Reform Benefits for Commercial Derivative Aircraft Acquisitions

The purpose of this thesis is to propose several specific process improvements to the U.S. Navy Flight Clearance process. It also makes recommendations for investment in test and evaluation infrastructure to better support commercial derivative aircraft acquisition for military use. Recent changes to Department of Defense acquisition regulations have increased alternatives available to the services to meet military operational requirements. In order to reduce cost and cycle times, the military services are turning more and more to acquiring commercially developed and certified aircraft to meet military requirements

Third Yearly Activity Report

The calculation work performed during the 3rd project year in WP2 as well as the R&D activities carried out in WP3, WP4 and WP5 are described in this report. In addition, the work dedicated to the project management (WP1) as well as to WP6 regarding the dissemination/communication activities and the education/training program (e.g. the follow-up of the mobility program between different organizations in the consortium, training on simulation tools and activities accomplished by PhD/post-doctoral students) is also reported