Chemical Kinetic Insights into the Octane Number and Octane Sensitivity of Gasoline Surrogate Mixtures

Gasoline octane number is a significant empirical parameter for the optimization and development of internal combustion engines capable of resisting knock. Although extensive databases and blending rules to estimate the octane numbers of mixtures have been developed and the effects of molecular structure on autoignition properties are somewhat understood, a comprehensive theoretical chemistry-based foundation for blending effects of fuels on engine operations is still to be developed. In this study, we present models that correlate the research octane number (RON) and motor octane number (MON) with simulated homogeneous gas-phase ignition delay times of stoichiometric fuel/air mixtures. These correlations attempt to bridge the gap between the fundamental autoignition behavior of the fuel (e.g., its chemistry and how reactivity changes with temperature and pressure) and engine properties such as its knocking behavior in a cooperative fuels research (CFR) engine. The study encompasses a total of 79 hydrocarbon gasoline surrogate mixtures including 11 primary reference fuels (PRF), 43 toluene primary reference fuels (TPRF), and 19 multicomponent (MC) surrogate mixtures. In addition to TPRF mixture components of iso-octane/n-heptane/toluene, MC mixtures, including n-heptane, iso-octane, toluene, 1-hexene, and 1,2,4-trimethylbenzene, were blended and tested to mimic real gasoline sensitivity. ASTM testing protocols D-2699 and D-2700 were used to measure the RON and MON of the MC mixtures in a CFR engine, while the PRF and TPRF mixtures' octane ratings were obtained from the literature. The mixtures cover a RON range of 0-100, with the majority being in the 70-100 range. A parametric simulation study across a temperature range of 650-950 K and pressure range of 15-50 bar was carried out in a constant-volume homogeneous batch reactor to calculate chemical kinetic ignition delay times. Regression tools were utilized to find the conditions at which RON and MON best correlate with simulated ignition delay times. Furthermore, temperature and pressure dependences were investigated for fuels with varying octane sensitivity. This analysis led to the formulation of correlations useful to the definition of surrogates for modeling purposes and allowed one to identify conditions for a more in-depth understanding of the chemical phenomena controlling the antiknock behavior of the fuels

Disinfection of Ocular Cells and Tissues by Atmospheric-Pressure Cold Plasma

Background: Low temperature plasmas have been proposed in medicine as agents for tissue disinfection and have received increasing attention due to the frequency of bacterial resistance to antibiotics. This study explored whether atmospheric-pressure cold plasma (APCP) generated by a new portable device that ionizes a flow of helium gas can inactivate ocular pathogens without causing significant tissue damage. Methodology and Principal Findings: We tested the APCP effects on cultured Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Candida albicans, Aspergillus fumigatus and Herpes simplex virus-1, ocular cells (conjunctival fibroblasts and keratocytes) and ex-vivo corneas. Exposure to APCP for 0.5 to 5 minutes significantly reduced microbial viability (colony-forming units) but not human cell viability (MTT assay, FACS and Tunel analysis) or the number of HSV-1 plaque-forming units. Increased levels of intracellular reactive oxygen species (ROS) in exposed microorganisms and cells were found using a FACS-activated 2',7'-dichlorofluorescein diacetate probe. Immunoassays demonstrated no induction of thymine dimers in cell cultures and corneal tissues. A transient increased expression of 8-OHdG, genes and proteins related to oxidative stress (OGG1, GPX, NFE2L2) was determined in ocular cells and corneas by HPLC, qRT-PCR and Western blot analysis. Conclusions: A short application of APCP appears to be an efficient and rapid ocular disinfectant for bacteria and fungi without significant damage on ocular cells and tissues, although the treatment of conjunctival fibroblasts and keratocytes caused a time-restricted generation of intracellular ROS and oxidative stress-related responses

Bacterial Inactivation of Wound Infection in a Human Skin Model by Liquid-Phase Discharge Plasma

Background: We investigate disinfection of a reconstructed human skin model contaminated with biofilm-formative Staphylococcus aureus employing plasma discharge in liquid. Principal Findings: We observed statistically significant 3.83-log10 (p,0.001) and 1.59-log10 (p,0.05) decreases in colony forming units of adherent S. aureus bacteria and 24 h S. aureus biofilm culture with plasma treatment. Plasma treatment was associated with minimal changes in histological morphology and tissue viability determined by means of MTT assay. Spectral analysis of the plasma discharge indicated the presence of highly reactive atomic oxygen radicals (777 nm and 844 nm) and OH bands in the UV region. The contribution of these and other plasma-generated agents and physical conditions to the reduction in bacterial load are discussed. Conclusions: These findings demonstrate the potential of liquid plasma treatment as a potential adjunct therapy for chronic wounds

Autoignition quality of gasoline fuels in partially premixed combustion in diesel engines

A single-cylinder diesel engine has been run on gasolines of different octane numbers and on model fuels, mixtures of iso-octane, n-heptane and toluene, at different operating conditions. The autoignition quality of the fuel is best described by an Octane Index, OI = (1 - K) . RON + K . MON for fuels in the gasoline autoignition range where RON and MON are, respectively, the Research and Motor Octane numbers and K is an empirical constant which is measured to be negative. Hence for a given RON, a non-paraffinic fuel, of lower MON, will have higher OI and more resistance to autoignition. For a given operating condition, ignition delay increases non-linearly with OI and changes little over the autoignition range of practical diesel fuels. Heat release following the autoignition is influenced by the stratification which will increase as the time between the end of injection and start of combustion decreases and combustion phasing parameters such as Combustion Delay, the difference between the 50% burn time and the start of injection, become less correlated with fuel autoignition quality. Higher ignition delays facilitate premixed combustion in the diesel engine. If two fuels have similar combustion phasing at the same injection timing, their emissions performance is also similar. Hence a good surrogate for gasoline in partially premixed compression ignition engines is a mixture of toluene, iso-octane and n-heptane with the same RON and MON. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved