Search results

Forests too thick with fuels that are too continuously spread to resist fire are common throughout the west. After a century or more of actively working to suppress fire across the landscape, we now recognize that fire is a part of our forests, shrublands, and range, and that it will come whether we wish it or not. At last, managers must realize forests cannot be fire-proofed (DellaSala, Williams, Williams, & Franklin, 2004). We must work with fire rather than against it.

The aim of this paper is to find the electrical representation of a solid oxide fuel cell (SOFC) that enables the application of typical exploitation characteristics of fuel cells for estimation of fuel cell parameters (for example, exchange current) and easy analysis of phenomena occurred during the fuel cell operation.

Three-layer structure of an SOFC, where a thin semi-conducting layer of electrolyte separates the anode from the cathode, shows a strong similarity to typical semiconductor devices built on the basis of P-N junctions, like diodes or transistors. Current–voltage (I-V) characteristics of a fuel cell can be described by the same mathematical functions as I-V plots of semiconductor devices. On the basis of this similarity and analysis of impedance spectra of a real fuel cell, two electrical representations of the SOFC have been created.

The simplified electrical representation of SOFC consists of a voltage source connected in series with a diode, which symbolizes a voltage drop on a cell cathode, and two resistors. This model is based on the similarity of Butler-Volmer to Shockley equation. The advanced representation comprises a voltage source connected in series with a bipolar transistor in close to saturation mode and two resistors. The base-emitter junction of the transistor represents voltage drop on the cell cathode, and the base-collector junction represents voltage drop on the cell anode. This model is based on the similarity of Butler-Volmer equation to Ebers-Moll equation.

The proposed approach based on the Shockley and Ebers-Moll formulas enables the more accurate estimation of the ion exchange current and other fuel cell parameters than the approach based on the Butler-Volmer and Tafel formulas. The usability of semiconductor models for analysis of SOFC operation was proved. The models were successively applied in a new design of a planar ceramic fuel cell, which features by reduced thermal capacity, short start-up time and limited number of metal components and which has become the basis for the SOFC stack design.

In this article the requirement leading to the design is discussed and this is followed by a general description of the aircraft and its operating efficiency. The accommodation is described, with particular reference to the flight deck and equipment. The various systems and installations are next reviewed; followed by a detailed description of the various structural components, which, in many cases, have been designed round these systems. The development work that has been done in order to allow design and construction to be completed will be described in some detail in a later article.

Reductions in emissions intensity have been expressed in commitments of many countries’ intended nationally determined contribution. Energy structure adjustment is one of the main approaches to reduce carbon emissions. This paper aims to study the causal relationship between carbon emission intensity and energy consumption structure in China based on path analysis.

After data collection, this paper performs correlation analysis, regression and path analysis.

Correlation results display clear collinearity among energy structure variables. Regression finds that coal, oil, natural gas and technology can be used as indicators for carbon intensity while primary electricity has been excluded. Path analysis shows that coal had the largest direct and positive impact on emission intensity. Natural gas had a positive direct and negative indirect effect through its negative relationship with coal on emission intensity. Technology has the largest negative elasticity while all fossil energies are positive. Results indicate a negative effect of energy structure adjustment on China’s national carbon intensity.

Given the major role of China in global climate change mitigation, significant future reductions in China’s CO₂ emissions will require transformation toward low-carbon energy systems. Considering the important role in mitigating global climate change, China needs to transition toward a low-carbon energy system to significantly reduce its carbon intensity in the future.

The purpose of the conducted investigations is assessment of performance improvement of hybrid gas-turbine engine (HGTE) based on solid oxide fuel cell (SOFC) using cheaper and environmental alternative fuels (AF) such as liquid methane and propane – butane mixture (propane – butane). This paper also assessed the efficiency of mid-flight propulsion system (PS) based on HGTE for advanced short – medium hall aircrafts (SMHA) of 2025 (with level of parameters corresponding to technologies of 2025-2030 time period).

According to purposes of this paper, following are conducted: Analysis of properties of conventional and advanced aviation fuels, updating of architectures and parameters of energy system of HGTE based on SOFC using different fuels (kerosene, methane and propane – butane). Examination of rational architectures and updating of possible design parameters of HGTE using different types of fuel. Assessment of efficiency of PS with HGTE using different fuels under aircraft criteria. Assessment of emission of harmful substances and acoustical efficiency of SMHA with HGTE using different fuels.

Improvement of technical and environmental performances of SMHA with HGTE based on SOFC using AF in comparison with turbofan is shown.

Accuracy of research results is defined by a number of the adopted aircraft and engine restrictions, as well as accuracy of prediction concerning to the improvement of integral characteristics of elements SMHA and PS with HGTE for 2025.

Advantages of HGTE based on SOFC create good preconditions for initiation of works on development of new-generation aircrafts using AF after 2025.

Development of SOFC technologies result in evolution of new high-economic and environmental friendly hybrid gas-turbine PS for aircrafts using AF, Improvement of an environmental situation around the airport, decrease of CO₂ emission for full-flight cycle, creation of scientific and technological base for transition to electric PS of full electric aircraft.

Research results show that application of AF increases efficiency of electrochemical generator (ECG) based on SOFC and fuel efficiency of whole engine, which enable to use HGTE for PS of advanced aircrafts more effectively than turbofan. As distinct from storage battery (Bradley et al., 2010) and ECG based on Polymer Electrolyte Membrane Fuel Cell (Horyson Energy Systems, 2010), specific characteristics of ECG based on SOFC using methane allow to design PS for SMHA of 2025.

Development of the Lockheed supersonic transport has followed the basic philosophy that an advance in air travel in terms of speed and economics should be accompanied by similar advances in aeroplane safety and flying qualities. To achieve these objectives, Lockheed's SST design work has been concentrated for many years on the development of a fixed‐wing design. The present configuration—called a double delta—provides a simple high lift system with low wing loading, excellent low speed stability and control, and large favourable ground effects in landing, with inherent advances in operational simplicity and safety.

This study aims to assess future prospects for Russian energy exports until 2040, as global energy markets are undergoing major changes, with possible impacts on Russia.

Qualitative and quantitative approaches are integrated under a proposed foresight framework. The qualitative method involves an expert survey aimed at identifying major energy trends and their influence on Russia. As the trends are validated, an algorithm is proposed to assess the contribution of separate trends to Russian energy exports.

Experimental quantitative scenarios are conducted to assess the prospects for Russian energy exports until 2040 under the given exogenous scenario calculations of the IEA. Factor analysis allows for an assessment of the contribution of separate factors in dynamics of net energy imports into the regional economies. The future prospects for fossil fuels’ exports on regional markets are considered. Priority markets for Russian energy exporters are identified.

The results of the paper may be used by decision-makers for adjustments in the system of government policy or corporate strategy.

The paper provides an algorithm to assess energy export flows to macroregions based upon the synthesis of quantitative and qualitative information. Experimental scenario calculations of the Russian fossil fuels’ exports are provided. Strategic decision-making map is elaborated.

Up to a few years ago the work in the aeronautical development department of the Brazilian Technical Centre had failed to achieve one of its major objectives, which was to produce a nucleus of trained aeronautical Brazilian engineers. This was largely due to lack of co‐operation from contracted foreign personnel and from opposition in some quarters where it was considered that the projects undertaken were over ambitious and unlikely to produce a successful production aircraft of immediate national use in a reasonable time period. The failure to achieve this nucleus team was a great disappointment to the Brazilians in their aim towards developing their own stable national aeronautical industry since this team would obviously have been the backbone of the envisaged industry.

Availability of military systems is of major concern for military planners at both tactical (battle) level and at strategic level (long‐term national planning). Availability factors critically affect the operational effectiveness during military operations. Military systems are complex and lend themselves to simulation approach for availability estimation as analytical solutions are extremely difficult. The purpose of this paper is to discuss the method of systems modeling to approach the simulation for availability estimation of military systems.

Availability measures are needed for two main domains of application: peacetime operations and battlefield situations. Availability measures include not only inherent availability of interest to designers/manufacturers, but also operational availability and field/service availability. The simulation approach adopted here involves discrete event simulation (DES) techniques using Monte Carlo methods since a network of events can be included in the model. A system engineering approach is emphasized, starting with system representation and characterisation, and using system aggregation techniques.

Modeling involves hierarchical models and network diagrams for events. First the system is described by a hierarchical model; the events and transitions are represented with state transition diagrams (STD). The simulation scheme would be based on initial resources or inventory as military operations proceed, with random variates for event times or rates. The availability as a function of time A(t) is arrived at. The reliability and maintainability models are simulated with probability distributions or using empirical distributions. The methods of data collection and analysis, and sensitivity analysis are mentioned. The methodology is explained with two case studies from the authors' work. The approaches of other workers in recent years are summarised.

The paper shows that the simulation models can suitably be modified to include their applications for army and navy military operations. Also, with proper data on all major subsystems of interest for the weapon platform and accurate past war data, it is possible to fine‐tune the models for online use during military campaigns. The availability figures thus obtained may also be used for procurement decisions for long‐term and strategic planning.