Simultaneous Efficiency, NOx, and Smoke Improvements through Diesel/Gasoline Dual-Fuel Operation in a Diesel Engine

Diesel/gasoline dual-fuel combustion uses both gasoline and diesel fuel in diesel engines to exploit their different reactivities. This operation combines the advantages of diesel fuel and gasoline while avoiding their disadvantages, attains spatially stratified low temperature combustion (LTC), and yields very low NOx and PM emissions while maintaining good efficiency. It is promising in solving the problems of conventional LTC through better control of ignition and combustion. The benefits of dual-fuel operation and the potential of using gasoline fumigation to realize these benefits provide the major motivation to this research. This research is aimed at using gasoline fumigation in a medium-duty diesel engine to identify and quantify the influencing factors of diesel/gasoline dual-fuel LTC on engine efficiency and emissions. The factors include gasoline fraction, injection settings, rail pressure, intake pressure, and EGR level. This objective was realized through a series of experimental tests done at 1400 rpm and three loads, including both diesel baseline tests and dual-fuel tests. First, design of experiments and relevant statistical techniques were applied to tests. Twenty-three best models between 6 factors (intake pressure, rail pressure, SOI for diesel baseline tests, SOI for dual-fuel tests, EGR level, and gasoline fraction) and 5 targets (efficiency, NOx, smoke number, HC, and CO) were obtained through regression of test data. Confirmation tests were done based on best models. Generally, the observations are improved NOx and smoke emissions, but unimproved or deteriorated efficiency, HC and CO emissions. The optimization effort makes some achievements, but needs further improvement. The influence of each factor is analyzed. The measures to get better models are explained. Second, parametric studies of gasoline fraction and injection timing were done to find their influence on efficiency and emissions. Efficiency generally decreases slightly as gasoline fraction increases or injection timing is retarded. Generally, increasing gasoline fraction is beneficial for NOx and smoke emissions, but HC and CO emissions deteriorate. An advance in injection timing, however, has the opposite influence. Finally, individual cycle data were analyzed to study cyclic variability (CV) and its influence on dual-fuel efficiency and emissions. Factors causing or influencing CV were identified. The CV in dual-fuel operation is more serious than that in diesel operation, in terms of magnitude. Most of the test data studied do not have strong determinism, and the influence of gasoline addition is small

A review of closed-form Cramér-Rao Bounds for DOA estimation in the presence of Gaussian noise under a unified framework

The Cramér-Rao Bound (CRB) for direction of arrival (DOA) estimation has been extensively studied over the past four decades, with a plethora of CRB expressions reported for various parametric models. In the literature, there are different methods to derive a closed-form CRB expression, but many derivations tend to involve intricate matrix manipulations which appear difficult to understand. Starting from the Slepian-Bangs formula and following the simplest derivation approach, this paper reviews a number of closed-form Gaussian CRB expressions for the DOA parameter under a unified framework, based on which all the specific CRB presentations can be derived concisely. The results cover three scenarios: narrowband complex circular signals, narrowband complex noncircular signals, and wideband signals. Three signal models are considered: the deterministic model, the stochastic Gaussian model, and the stochastic Gaussian model with the a priori knowledge that the sources are spatially uncorrelated. Moreover, three Gaussian noise models distinguished by the structure of the noise covariance matrix are concerned: spatially uncorrelated noise with unknown either identical or distinct variances at different sensors, and arbitrary unknown noise. In each scenario, a unified framework for the DOA-related block of the deterministic/stochastic CRB is developed, which encompasses one class of closed-form deterministic CRB expressions and two classes of stochastic ones under the three noise models. Comparisons among different CRBs across classes and scenarios are presented, yielding a series of equalities and inequalities which reflect the benchmark for the estimation efficiency under various situations. Furthermore, validity of all CRB expressions are examined, with some specific results for linear arrays provided, leading to several upper bounds on the number of resolvable Gaussian sources in the underdetermined case

Development of Reduced-Order Models for Engine Applications

Detailed chemical kinetics is critical for accurate prediction of complex flame behaviors, such as ignition and extinction in engine applications, but difficult to be applied in multi-dimensional flame simulations due to their large sizes. Reduced-order models are needed in such cases to enable high fidelity combustion simulations. This dissertation is focused on developing new model reduction strategies and reduced-order models for engine combustion applications. First, a linearized error propagation (LEP) method for skeletal mechanism reduction is proposed. LEP is based on Jacobian analysis of perfectly stirred reactors (PSR) and can more accurately predict the propagation of small reduction errors compared with the previous methods of directed relation graph (DRG) and DRG with error propagation (DRGEP). Skeletal models generated by using LEP are further validated for auto-ignition and 1-D laminar premixed flames to demonstrate the feasibility of reaction state sampling using only PSR for mechanism reduction. Second, a direct method is developed to accurately and efficiently compute the ignition and extinction turning points of PSR by solving a local optimization problem formulated based on analytic Jacobian. It is shown that the direct method features significantly better accuracy and efficiency compared with the continuation methods that march along the S-curves. Third, reduced and skeletal mechanisms for gasoline surrogates with and without ethanol are developed based on a 1389-species detailed mechanism developed by the Lawrence Livermore National Laboratory (LLNL). The skeletal reduction was performed with DRG, sensitivity analysis, isomer lumping, and the time-scale based reduction is based on linearized quasi-steady-state approximations. The skeletal and reduced mechanisms are extensively validated against the detailed mechanism and available experimental data for ignition delay time and flame speed. The skeletal mechanism is employed in cooperative fuel research engine simulations and the results agree well with experimental data. Lastly, skeletal mechanisms are generated for three gasoline/bio-blend-stock surrogates respectively based on a 2878-species detailed LLNL mechanism for engine simulations. An upgraded solver combining analytical Jacobian and sparse matrix techniques is employed to accelerate the reduction process, such that the reduction time becomes linearly proportional to the mechanism size and a speedup factor of approximately 100 is achieved

High-throughput Exploration of Glass Formation via Laser Deposition and the Study of Heterogeneous Microstructure in a Bulk Metallic Glass Alloy

Bulk metallic glasses are a relatively novel class of engineering alloys characterized by a disordered atomic structure devoid of long-range translational symmetry. Compared to crystalline alloys, the confluence of metallic bonding and amorphous structure imbues bulk metallic glasses with a unique set of properties that makes them particularly attractive for a wide variety of structural applications. Such properties include exceptional yield strengths, high elastic resilience, resistance to corrosion, and in particular, the unparalleled ability among metals to be thermoplastically formed across a wide range of length scales when heated above the glass transition temperature. Formation of metallic glass from a molten liquid depends on whether cooling is sufficiently rapid to bypass crystallization and vitrify into an amorphous solid; for a given alloy composition, the ease with which full vitrification can occur upon cooling from the liquid state is termed the alloy\u27s glass forming ability. Unfortunately, relatively few excellent glass formers have been reported in the vast, multicomponent composition space in which they reside. The apparent slowness of progress may be attributed largely to the inefficiency of the one-at-a-time experimental approach to discovery and design. In this thesis work, a high-throughput combinatorial methodology was developed to expedite the discovery process of new bulk metallic glasses. Laser deposition was used to fabricate continuously-graded composition libraries of Cu-Zr and Cu-Zr-Ti alloys. By processing the libraries with a range of laser heat input, the best glass formers in each alloy system could be efficiently and systematically deduced. Furthermore, instrumented nanoindentation performed on the libraries enabled rapid evaluation of mechanical property trends. Despite boasting high strengths, monolithic bulk metallic glasses generally suffer from an intrinsic lack of damage tolerance compared to other high performance alloys. Recent studies indicate that the macroscopic deformation behavior of the material may be controlled by structural heterogeneities, although the exact nature and origin of the heterogeneities remain ambiguous. To further the present knowledge, the heterogeneous microstructure of a zirconium-based bulk metallic glass was investigated with instrumented nanoindentation and dynamic modulus mapping. Significant spatial variations in the mechanical properties measured by both techniques suggests a hierarchical arrangement of structural/mechanical heterogeneities in bulk metallic glasses. Moreover, a previously unobserved elastic microstructure, comprising an interconnected network of elastic features, was revealed by dynamic modulus mapping. Despite the absence of visible contrast when imaged with electron microscopy, the aligned morphology of the elastic features and their sensitivity to thermal processing conditions imply the occurrence of spinodal decomposition in the supercooled liquid prior to glass formation. Finally, based on analysis of load-displacement data from nanoindentation experiments performed throughout the thesis work, a new parameter, the plastic work ratio, was proposed as a figure of merit for quantifying the intrinsic plasticity of monolithic metallic glass alloys

Optical Deformation of Microdroplets at Ultralow Interfacial Tension

What is the shape of a droplet? Its interfacial tension dictates that it is very close to a perfect sphere. Herein, the interfacial tension is reduced to ultralow values (0.1 - 100 uN/m) by careful formulation of surfactant additives, such as for mixtures that form microemulsions. The droplet need not be spherical but can accommodate external forces of a similar magnitude. The control and precision of forces afforded simply by light - in the form of highly focused Nd:YAG laser beams - are exploited in this work to deform hydrocarbon oil-in-water emulsion droplets of 1-10 um diameter. To this end, a novel, integrated platform for microfluidic generation, optical deformation and 3D fluorescent imaging of droplets is presented. Previous attempts to characterise optically-controlled microdroplet shapes have been limited to 2D projections. Here, that ambiguity is resolved using 3D confocal laser scanning- and structured illumination microscopy. 2D and 3D arrays of up to four Gaussian point traps are generated by holograms and acousto-optics. A variety of regular, prolate, oblate and asymmetric shapes are produced and correlated with parameters such as optocapillary number, trap separation and capillary length. Exotic shapes exhibiting zero or negative mean and Gaussian curvatures are presented alongside their brightfield counterparts. The complex phase behaviour of emulsion droplets and their parent phases is observed to couple strongly to thermal absorption of the beams. The rich interfacial chemistry, its relation to the forces determining droplet shape and the surprising ability to create nanofluidic networks between droplets are investigated

Present and Future of Gravitational Wave Astronomy

The first detection on Earth of a gravitational wave signal from the coalescence of a binary black hole system in 2015 established a new era in astronomy, allowing the scientific community to observe the Universe with a new form of radiation for the first time. More than five years later, many more gravitational wave signals have been detected, including the first binary neutron star coalescence in coincidence with a gamma ray burst and a kilonova observation. The field of gravitational wave astronomy is rapidly evolving, making it difficult to keep up with the pace of new detector designs, discoveries, and astrophysical results. This Special Issue is, therefore, intended as a review of the current status and future directions of the field from the perspective of detector technology, data analysis, and the astrophysical implications of these discoveries. Rather than presenting new results, the articles collected in this issue will serve as a reference and an introduction to the field. This Special Issue will include reviews of the basic properties of gravitational wave signals; the detectors that are currently operating and the main sources of noise that limit their sensitivity; planned upgrades of the detectors in the short and long term; spaceborne detectors; a data analysis of the gravitational wave detector output focusing on the main classes of detected and expected signals; and implications of the current and future discoveries on our understanding of astrophysics and cosmology

Publications of the Jet Propulsion Laboratory - July through December 1970

Bibliography of technical literature resulting from aerospace research and development at Jet Propulsion Laboratorie

The Telecommunications and Data Acquisition

This quarterly publication provides archival reports on developments in programs managed by JPL's Office of Telecommunications and Data Acquisition (TDA). In space communications, radio navigation, radio science, and ground-based radio and radar astronomy, it reports on activities of the Deep Space Network (DSN) in planning, supporting research and technology, implementation, and operations. Also included are standards activity at JPL for space data and information systems and reimbursable DSN work performed for other space agencies through NASA. The preceding work is all performed for NASA's Office of Space Communications (OSC)