Prediction of Spark Ignition Performance in an Industrial Gas Turbine Combustor

Abstract Spark ignition performance of an annular combustor has been analyzed using computational modeling approach. Main steps of this approach include: (1) LES of the combustor non-reacting flow field, (2) using time-averaged LES results in a stochastic code in order to identify probable propagation behavior of the flame front using Lagrangian particle tracking, and (3) repeating the computations by an engineering approach and prediction of the combustor lean light-off (LLO) limit. By using this approach, effects of the ignition system location and specifications, fuel type and composition, and operating conditions on the gas turbine ignition performance can be evaluated effectively. Corresponding author: [email protected] Proceedings of the European Combustion Meeting 2015 Introduction Ignition is the process of transferring a flammable mixture from the non-reacting state to the selfsustaining combustion. Ignition is a transient phenomenon in which a complex interaction of chemical and physical processes occurs. Ignition in a flammable environment can be achieved by two general methods: forced ignition and self-ignition. During the forced ignition, a small volume of the mixture is ignited by an external force and the flame spreads across the whole system if the flame propagation conditions exist. In self-ignition or auto-ignition process, there is no local ignition source and the whole mixture ignites simultaneously Currently, practical gas turbine engine ignition systems include spark ignition (electrical spark and laser-induced spark or LIS) and torch systems (including both flame and plasma torches) Different studies have shown that the spark ignition in an annular gas turbine combustor is conducted at three phases. At the first phase, with starting discharge process and through breakdown, arc discharge, and glow discharge stages a flame kernel with sufficient size and temperature forms. At the second phase, this flame core spreads and the continuous spread of the flame from this kernel fills the primary combustion zone o

Invariant electrical conductivity upon thermal ageing of a crosslinked copolymer blend for high voltage insulation

Click chemistry type reactions between polyethylene-based copolymers are a promising and by-product free alternative to peroxide crosslinking of low-density polyethylene, which is widely used as an insulation material for high-voltage power cables. Here, the impact of thermal ageing on the long-term stability of the thermo-mechanical and dielectric properties of a copolymer blend is evaluated that can be cured through a by-product free reaction between the epoxy and carboxylic acid functional groups attached to the polyethylene backbone. It is observed that ageing at 90 degrees C in air for up to 2500 h does not affect the direct current (DC) electrical conductivity of about 3 x 10(-14) S m(-1), provided that a suitable antioxidant is added that prevents the thermo-oxidative degradation of the polyethylene backbone. Furthermore, the material maintains its thermo-mechanical properties upon ageing such as a high ductility at room temperature and a stiffness of about 1 MPa above the melting temperature of polyethylene. Evidently, the use of click chemistry type reactions is a promising strategy for the design of new high-voltage insulation materials that can be cured without the formation of by-products

Highly insulating thermoplastic blends comprising a styrenic copolymer for direct-current power cable insulation

The impact of the composition of blends comprising low-density polyethylene (LDPE), isotactic polypropylene (PP) and a styrenic copolymer additive on the thermomechanical properties as well as the direct-current (DC) electrical and thermal conductivity is investigated. The presence of 5 weight percent (wt%) of the styrenic copolymer strongly reduces the amount of PP that is needed to enhance the storage modulus above the melting temperature of LDPE from 40 to 24 wt%. At the same time, the copolymer improves the consistency of the thermomechanical properties of the resulting ternary blends. While both the DC electrical and thermal conductivity strongly decrease with PP content, the addition of the styrenic copolymer appears to have little influence on either property. Evidently, PP in combination with small amounts of a styrenic copolymer not only allows to reinforce LDPE at elevated temperatures but also functions as an electrical conductivity-reducing additive, which makes such thermoplastic ternary formulations possible candidates for the insulation of high-voltage power cables

Highly insulating thermoplastic nanocomposites based on a polyolefin ternary blend for high-voltage direct current power cables

Octyl-silane-coated Al2O3 nanoparticles are found to be a promising conductivity-reducing additive for thermoplastic ternary blends comprising low-density polyethylene (LDPE), isotactic polypropylene and a styrenic copolymer. The ternary blend nanocomposites were prepared by compounding the blend components together with an LDPE-based masterbatch that contained the nanoparticles. The nanoparticles did not affect the superior stiffness of the ternary blends, compared to neat LDPE, between the melting temperatures of the two polyolefins. As a result, ternary blend nanocomposites comprising 38 wt% polypropylene displayed a storage modulus of more than 10 MPa up to at least 150 degrees C, independent of the chosen processing conditions. Moreover, the ternary blend nanocomposites featured a low direct-current electrical conductivity of about 3 x 10(-15) S m(-1) at 70 degrees C and an electric field of 30 kV mm(-1), which could only be achieved through the presence of both polypropylene and Al2O3 nanoparticles. This synergistic conductivity-reducing effect may facilitate the design of more resistive thermoplastic insulation materials for high-voltage direct current (HVDC) power cables

“At ‘Amen Meals’ It’s Me and God” Religion and Gender: A New Jewish Women’s Ritual

New ritual practices performed by Jewish women can serve as test cases for an examination of the phenomenon of the creation of religious rituals by women. These food-related rituals, which have been termed ‘‘amen meals’’ were developed in Israel beginning in the year 2000 and subsequently spread to Jewish women in Europe and the United States. This study employs a qualitative-ethnographic methodology grounded in participant-observation and in-depth interviews to describe these nonobligatory, extra-halakhic rituals. What makes these rituals stand out is the women’s sense that through these rituals they experience a direct con- nection to God and, thus, can change reality, i.e., bring about jobs, marriages, children, health, and salvation for friends and loved ones. The ‘‘amen’’ rituals also create an open, inclusive woman’s space imbued with strong spiritual–emotional energies that counter the women’s religious marginality. Finally, the purposes and functions of these rituals, including identity building and displays of cultural capital, are considered within a theoretical framework that views ‘‘doing gender’’ and ‘‘doing religion’’ as an integrated experience

Large-scale unit commitment under uncertainty: an updated literature survey

The Unit Commitment problem in energy management aims at finding the optimal production schedule of a set of generation units, while meeting various system-wide constraints. It has always been a large-scale, non-convex, difficult problem, especially in view of the fact that, due to operational requirements, it has to be solved in an unreasonably small time for its size. Recently, growing renewable energy shares have strongly increased the level of uncertainty in the system, making the (ideal) Unit Commitment model a large-scale, non-convex and uncertain (stochastic, robust, chance-constrained) program. We provide a survey of the literature on methods for the Uncertain Unit Commitment problem, in all its variants. We start with a review of the main contributions on solution methods for the deterministic versions of the problem, focussing on those based on mathematical programming techniques that are more relevant for the uncertain versions of the problem. We then present and categorize the approaches to the latter, while providing entry points to the relevant literature on optimization under uncertainty. This is an updated version of the paper "Large-scale Unit Commitment under uncertainty: a literature survey" that appeared in 4OR 13(2), 115--171 (2015); this version has over 170 more citations, most of which appeared in the last three years, proving how fast the literature on uncertain Unit Commitment evolves, and therefore the interest in this subject

Assessing the Scalability and Privacy of Energy Communities by Using a Large-Scale Distributed and Parallel Real-Time Optimization

In the context of the energy transition, energy communities are gaining increasing attention all over the world, in recent years. By participating in an energy community, prosumers may take a leading role in the energy transition and improve the self-consumption of renewable energy produced inside the community. Prosumers can carry out energy exchanges inside the energy community and provide ancillary services to the system operators, thus contributing to improve the efficiency and stability of the grid. A novel scalable, privacy-preserving, and real-time distributed parallel optimization is proposed to manage a large-scale energy community, considering energy exchanges inside the community according to the model of virtual self-consumption and the provision of ancillary services. The proposed method preserves the privacy of prosumers and allows the assessment of the impact of energy exchanges on the ancillary services provided by an energy community. Simulation results confirmed that the proposed method is superior in terms of privacy if compared with the equivalent centralized optimization and that it has a convergence rate higher than that of the splitting conic solver (SCS)