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

Stratigraphy and structure of the Horseshoe Gulch area, Etna and China Mountain quadrangles, California

The Horseshoe Gulch area includes 16 square miles in the Eastern Paleozoic Belt of the Klamath Mountains geologic province north of Callahan, California. Fossiliferous Late Ordovician and Silurian limestones and unfossiliferous greywackes, arkoses, shales, mudstones, schists, and phyllites, and other terrigenous clastic rocks are exposed in a broad fault zone in the area of study. It is concluded that the limestones represent a clear, stable, and relatively shallow water environment of deposition. These limestones are found associated with a geosynclinal sequence of rock units. Eleven mappable units grouped into upper and lower thrust plates, are recognized. The fault zone in the Horseshoe Gulch area, approximately one mile wide, is characterized by a prominent folded thrust fault that is part of the Mallethead Thrust. The Mallethead Thrust, whose age is at least post-Late Silurian in the area, has placed upper plate unfossiliferous, pre-Cretaceous age chlorite grade metamorphic rocks over the Early Paleozoic unmetamorphosed limestones and clastics of the lower plate. The trace of the Mallethead Thrust is very sinuous and irregular

Ice Core Record of Rising Lead Pollution in the North Pacific Atmosphere

A high-resolution, 8000 year-long ice core record from the Mt. Logan summit plateau (5300 m asl) reveals the initiation of trans-Pacific lead (Pb) pollution by ca. 1730, and a \u3e10-fold increase in Pb concentration (1981–1998 mean = 68.9 ng/l) above natural background (5.6 ng/l) attributed to rising anthropogenic Pb emissions from Asia. The largest rise in North Pacific Pb pollution from 1970–1998 (end of record) is contemporaneous with a decrease in Eurasian and North American Pb pollution as documented in ice core records from Greenland, Devon Island, and the European Alps. The distinct Pb pollution history in the North Pacific is interpreted to result from the later industrialization and less stringent abatement measures in Asia compared to North America and Eurasia. The Mt. Logan record shows evidence for both a rising Pb emissions signal from Asia and a trans-Pacific transport efficiency signal related to the strength of the Aleutian Low

The Effects of Flowline Length Evolution on Chemistry-Delta O-18 Profiles from Penny Ice Cap, Baffin Island, Canada

The isotopic and chemical signatures for ice-age and Holocene ice from Summit, Greenland and Penny Ice Cap, Baffin Island, Canada, arc compared. The usual pattern of low delta(18)O, high Ca2+ and high Cl- is presented in the Summit records, but Penny Ice Cap has lower than present Cl- in its ice-age ice. A simple extension of the Hansson model (Hansson, 1994) is developed and used to simulate these signatures. The low ice-age Cl- from Penny Ice Cap is explained by having the ice-age ice originating many thousands of km inland near the centre of the Laurentide ice sheet and much further from the marine sources. Summit\u27s flowlines all start close to the present site. The Penny Ice Cap early-Holocene delta(18)O\u27s had to be corrected to offset the Laurentide meltwater distortion. The analysis suggests that presently the Summit and Penny Ice Cap marine impurity originates about,500 km away, and that presently Penny Ice Cap receives a significant amount of local continental impurity

Ice Core Record of Rising Lead Pollution in the North Pacific Atmosphere

A high-resolution, 8000 year-long ice core record from the Mt. Logan summit plateau (5300 m asl) reveals the initiation of trans-Pacific lead (Pb) pollution by ca. 1730, and a \u3e 10-fold increase in Pb concentration (1981-1998 mean = 68.9 ng/l) above natural background (5.6 ng/l) attributed to rising anthropogenic Pb emissions from Asia. The largest rise in North Pacific Pb pollution from 1970-1998 (end of record) is contemporaneous with a decrease in Eurasian and North American Pb pollution as documented in ice core records from Greenland, Devon Island, and the European Alps. The distinct Pb pollution history in the North Pacific is interpreted to result from the later industrialization and less stringent abatement measures in Asia compared to North America and Eurasia. The Mt. Logan record shows evidence for both a rising Pb emissions signal from Asia and a trans-Pacific transport efficiency signal related to the strength of the Aleutian Low

Broadband dual-frequency comb spectroscopy in a rapid compression machine

We demonstrate fiber mode-locked dual frequency comb spectroscopy for broadband, high resolution measurements in a rapid compression machine (RCM). We apply an apodization technique to improve the short-term signal-to-noise-ratio (SNR), which enables broadband spectroscopy at combustion-relevant timescales. We measure the absorption on 24345 individual wavelength elements (comb teeth) between 5967 and 6133 cm-1 at 704 microsecond time resolution during a 12-ms compression of a CH4-N2 mixture. We discuss the effect of the apodization technique on the absorption spectra, and apply an identical effect to the spectral model during fitting to recover the mixture temperature. The fitted temperature is compared against an adiabatic model, and found to be in good agreement with expected trends. This work demonstrates the potential of DCS to be used as an in situ diagnostic tool for broadband, high resolution, measurements in engine-like environments.</p

Exploring the mycobacteriophage metaproteome: Phage genomics as an educational platform

Bacteriophages are the most abundant forms of life in the biosphere and carry genomes characterized by high genetic diversity and mosaic architectures. The complete sequences of 30 mycobacteriophage genomes show them collectively to encode 101 tRNAs, three tmRNAs, and 3,357 proteins belonging to 1,536 "phamilies" of related sequences, and a statistical analysis predicts that these represent approximately 50% of the total number of phamilies in the mycobacteriophage population. These phamilies contain 2.19 proteins on average; more than half (774) of them contain just a single protein sequence. Only six phamilies have representatives in more than half of the 30 genomes, and only three - encoding tape-measure proteins, lysins, and minor tail proteins - are present in all 30 phages, although these phamilies are themselves highly modular, such that no single amino acid sequence element is present in all 30 mycobacteriophage genomes. Of the 1,536 phamilies, only 230 (15%) have amino acid sequence similarity to previously reported proteins, reflecting the enormous genetic diversity of the entire phage population. The abundance and diversity of phages, the simplicity of phage isolation, and the relatively small size of phage genomes support bacteriophage isolation and comparative genomic analysis as a highly suitable platform for discovery-based education. © 2006 Hatfull et al

Recycling manure as cow bedding: potential benefits and risks for UK dairy farms

Material obtained from physical separation of slurry (recycled manure solids; RMS) has been used as bedding for dairy cows in dry climates in the US since the 1970s. Relatively recently, the technical ability to produce drier material has led to adoption of the practice in Europe under different climatic conditions. This review collates the evidence available on benefits and risks of using RMS bedding on dairy farms, with a European context in mind. There was less evidence than expected for anecdotal claims of improved cow comfort. Among animal health risks, only udder health has received appreciable attention. There are some circumstantial reports of difficulties of maintaining udder health on RMS, but no large scale or long term studies of effects on clinical and subclinical mastitis have been published. Existing reports do not give consistent evidence of inevitable problems, nor is there any information on clinical implications for other diseases. The scientific basis for guidelines on management of RMS bedding is limited. Decisions on optimum treatment and management may present conflicts between control of different groups of organisms. There is no information on the influence that such 'recycling' of manure may have on pathogen virulence. The possibility of influence on genetic material conveying antimicrobial resistance is a concern, but little understood. Should UK or other non-US farmers adopt RMS, they are advised to do so with caution, apply the required strategies for risk mitigation, maintain strict hygiene of bed management and milking practices and closely monitor the effects on herd health

Deep Eutectic Solvents (DESs) and their applications [forthcoming]

Deep Eutectic Solvents (DESs) and Their Application

LTC (Low-Temperature Combustion) Analysis of PCCI (Premixed Charge Compression Ignition) with n-Butanol and Cotton Seed Biodiesel Versus Combustion and Emissions Characteristics of Their Binary Mixtures

Direct injection (DI) of cotton seed biodiesel (CS100) with port fuel injection (PFI) of n-butanol was used for producing Premixed Controlled Compression Ignition (PCCI) to achieve low-temperature combustion (LTC) and obtain lower gaseous emissions in comparison to ULSD#2 (ultra-low sulfur diesel). PFI engine operation was compared to the combustion of binary mixtures of the same fuels reflecting the same weight ratio of high reactivity (CS100) and low reactivity (n-butanol) fuels. The supercharged engine was operated at constant speed and load with 20% exhaust gas recirculation (EGR). When compared to ULSD#2 reference, the ignition delay of 50% n-butanol and 50% CS100 binary mixture increased by 12% while the 50% n-butanol PFI with 50% CS100 DI led to a 17% decrease in ignition delay. Emissions of soot and nitrogen oxides were simultaneously improved using the PCCI strategy, reducing by 84% and 17%, respectively, given lower peak in-cylinder temperatures and increased oxygenation of the mixture. Carbon monoxide (CO) and unburned hydrocarbons (UHC) increased by several orders of magnitude as a downside of dual fuel injection; ringing intensity, however, improved, decreasing by 30% when using 50% n-butanol PFI in comparison to the ULSD#2 baseline given a smoother pressure gradients. Energy specific fuel consumption for CS50Bu50 (50% ULSD-50% n-butanol blend) increased by 4.5% compared to ULSD#2. The mechanical efficiencies and the coefficient of variation (COV) of IMEP were maintained at 70% and 2.5% respectively, during PCCI, indicating stable operation with renewable fuels