Metric Geometry of Nonregular Weighted Carnot–Carathéodory Spaces

We investigate local and metric geometry of weighted Carnot–Carathéodory spaces which are a wide generalization of sub-Riemannian manifolds and arise in nonlinear control theory, subelliptic equations, etc. For such spaces, the intrinsic Carnot–Carathéodory metric might not exist, and some other new effects take place. We describe the local algebraic structure of such a space, endowed with a natural quasimetric (first introduced by A. Nagel, E. M. Stein, and S. Wainger) and compare local geometries of the initial Carnot–Carathéodory (CC) space and its tangent cone at some fixed (possibly nonregular) point. The main results of the present paper, in particular, the theorem on divergence of integral lines and other estimates obtained for the quasimetrics, are new even for the case of sub-Riemannian manifolds.     

Waste to energy – An evaluation of the environmental impact

The thermal treatment of waste with the heat recovery (Waste to Energy – WTE) provides us with clean and reliable energy in the form of heat as well as power. This has contributed to primary energy savings in conventional utility systems. Impact of WTE regarding the environmental issue is quantified in this paper. The evaluation focuses on the calculation of primary energy savings. A novel methodology is proposed. Then an assessment of the emission rate is made and results discussed. Real up-to-date municipal solid waste incinerator with nominal capacity 100 kt/y is involved in a case study. Benefit of its operation has been compared with other up-to-date utility concepts.     

Modelling of the gas-turbine colorless distributed combustion: An application to hydrogen enriched – kerosene fuel

This study examines hydrogen-enriched kerosene combustion under distributed regime in a gas turbine combustion chamber. With hydrogen enrichment, it is aimed at increasing combustion performance of those fuels. However, in this circumstance, it is obvious to increase the flame temperature with taking place hydrogen enrichment. Thus colorless distributed combustion (CDC), which is one of the advanced combustion techniques, can be suggested to control flame temperature with slowing down the reaction rate, resulting in ultra-low NO_X emissions and more uniform temperature distribution with a broadened flame. For this purpose, the hydrogen-enriched kerosene fuels were examined by modeling a CFD code using the eddy dissipation concept, the radiation model (P-1) and the turbulence model (standard k-ε). In this way, the thermal fields and the NO_X distributions have been obtained. The results showed that hydrogen enrichment increased the flame temperatures from about 2490 K to 2605 K at air-combustion conditions until 30% H₂, resulting in the NO_X levels predicted increased in the combustor. With reducing oxygen percentage the flame started to be the broadened one. The flame temperatures decreased, for instance, from about 2605 K to 2230 K at 15% O₂ for the 30% H₂ containing fuel. As a result of this, the NO_X levels reduced from about 30 ppm to the values lower than 1 ppm in the combustor. It is concluded that increments in temperature and NO_X levels with hydrogen can be suppressed with distributed regime, which enables that gas turbines can be operated at wider flammability limits with hydrogen enrichment.     

From financial to carbon diversification – The potential of physical gold

Gold is a well-known diversifier of financial risk with a long history as a physical asset. This paper analyzes whether gold provides additional environmental benefits in the portfolio context. We show that the addition of gold to a diversified equity portfolio does not only enhance the risk-return relationship but also its sustainability by reducing the portfolio's carbon emissions. If carbon emissions are fully accounted for at the production (firm) level, physical gold holdings have zero CO₂ emissions. Even if CO₂ emissions are fully assigned to physical gold holdings, gold becomes a CO₂ diversifier if held over longer periods. Our study highlights the critical role of physical assets and the investment horizon in the sustainability analysis of portfolios.     

Techno-economic analysis of using corn stover to supply heat and power to a corn ethanol plant – Part 2: Cost of heat and power generation systems

This paper presents a techno-economic analysis of corn stover fired process heating (PH) and the combined heat and power (CHP) generation systems for a typical corn ethanol plant (ethanol production capacity of 170 dam³). Discounted cash flow method was used to estimate both the capital and operating costs of each system and compared with the existing natural gas fired heating system. Environmental impact assessment of using corn stover, coal and natural gas in the heat and/or power generation systems was also evaluated. Coal fired process heating (PH) system had the lowest annual operating cost due to the low fuel cost, but had the highest environmental and human toxicity impacts. The proposed combined heat and power (CHP) generation system required about 137 Gg of corn stover to generate 9.5 MW of electricity and 52.3 MW of process heat with an overall CHP efficiency of 83.3%. Stover fired CHP system would generate an annual savings of 3.6 M$ with an payback period of 6 y. Economics of the coal fired CHP system was very attractive compared to the stover fired CHP system due to lower fuel cost. But the greenhouse gas emissions per Mg of fuel for the coal fired CHP system was 32 times higher than that of stover fired CHP system. Corn stover fired heat and power generation system for a corn ethanol plant can improve the net energy balance and add environmental benefits to the corn to ethanol biorefinery.     

Heat and mass transfer analysis of a suspension of reacting particles subjected to concentrated solar radiation – Application to the steam-gasification of carbonaceous materials

A chemical reactor for the steam-gasification of carbonaceous materials (e.g. coal, coke, biomass) using high-temperature solar process heat is modeled by means of a two-phase formulation that couples radiative, convective, and conductive heat transfer to the chemical kinetics for polydisperse suspensions of reacting particles. The governing mass and energy conservation equations are solved by applying advanced Monte–Carlo and finite-volume techniques with smoothing and underrelaxation. Validation is accomplished by comparing the numerically calculated temperatures, product compositions, and chemical conversions with the experimentally measured values obtained from testing a 5 kW solar reactor prototype in a high-flux solar furnace. A unique feature of the reactor concept is that the gas-particle flow is directly exposed to concentrated solar radiation, providing efficient radiative heat transfer to the reaction site for driving the high-temperature highly endothermic process.     

The seesaw of Germany's biofuel policy – Tracing the evolvement to its current state

Today, biofuels represent one of the most common options for larger scale substitution of conventional fuels. Due to the trans-sectoral nature of biofuels, a multitude of factors and actors determine the according policies of governments and the beliefs of societies. Especially since some impacts of biomass cultivation for bioenergy production are not yet fully understood. This article aims at showing the drivers that led to an introduction of biofuel policies in Germany and explains Germany's pioneering role in the promotion of bioenergy. Thereby the focus lies on the role of the main actors and their composition of so called discourse coalitions. The analysis indicates that the origin of the biofuel industry was a result of national and supranational market interventions, as well as it was intermittently an instrument of supporting renewable energies. Along the seesaw of Germany's biofuel policies seven discourse coalitions were identified who compete for discursive hegemony in order to gain political influence.     

Assessing the sustainability of Brazilian oleaginous crops – possible raw material to produce biodiesel

The aim of this paper is to make an emergy assessment of oleaginous crops cultivated in Brazil, available to produce biodiesel, in order to determine which crop is the most sustainable. This study evaluates conventional agro-chemical farms that produce rapeseed (canola), oil palm, soybean, sunflower and cotton. Rapeseed (canola) crop uses 40.41% of renewable energy and it is the most sustainable conventional oil crop; on the other hand, it is not widely produced in Brazil, probably due to climate restrictions or low market demand. The oil palm emergy indicators are contradictory: its emergy exchange ratio (EER) value is the lower, showing the possibility of fair exchange, and the low transformity value indicates high efficiency; however, it also has low renewability (28.31%), indicating a high dependency on agro-chemicals (basically fertilizers). Oil palm is a potential energy source due to its high agricultural productivity, but appropriate management is necessary to increase its sustainability and reduce the use of non-renewable resources.     

Fuel cell micro-CHP techno-economics: Part 2 – Model application to consider the economic and environmental impact of stack degradation

This article presents a literature review regarding the mechanisms of fuel cell degradation, accompanied by the reported range of observed degradation rates in experimental, demonstration and early commercial systems. It then synthesises and exploits this information to investigate the influence of degradation on the economic and environmental credentials of fuel cell micro-combined heat and power (micro-CHP) for the UK residential sector. The investigation applies a techno-economic model developed in the companion article designed to demarcate the key characteristics of commercially successful systems. Two distinct modes of degradation are examined; one proportional to power density in the stack, and the other proportional to thermal-cycling rate of the stack. It is found that limiting the power-density related degradation rate is very important from economic and environmental viewpoints, but thermal-cycling related degradation is less important when thermal energy storage is available because cycling can be avoided. Furthermore it is noted that techno-economic studies that ignore degradation can overestimate the marginal value of a micro-CHP system with respect to the conventional alternative by up to 45% and the CO₂ emissions reduction potential by up to 57%, for performance degradation rates of 2% per MW_eh output. This conclusion is noteworthy because most techno-economic analyses of fuel cells ignore degradation, potentially providing misleading results. Finally it is concluded that existing commercial degradation targets, such as the SECA targets, are appropriate for achieving marketable systems.     

Comparative analysis of various techniques to improve the performance of novel wheat germ oil – an experimental study

The current study aims to explore the opportunities of using the high viscous biofuel namely Wheat Germ oil (WGO) in a twin cylinder CI engine. High viscous fuels suffer from improper atomization leading to poor combustion and higher smoke emission. To address this problem, various techniques namely transesterification, fuel ionization and hydrogen induction were studied. WGO was converted to its ester which reduced the viscosity. Fuel ionization increases the vibrational frequency of the molecules, weakens the bonds and converted to ions, which increases the dispersion rate during injection and improves the combustion subsequently. Hydrogen is having faster flame speed and higher calorific value aids in combustion enhancement at its knock limited levels.The twin cylinder tractor engine selected for this experiment runs at a constant speed of 1500 rpm. The engine was run using diesel to achieve the preferred warm-up condition in order to use WGO, which hada cold starting problem. Tests were conducted with wheat germ biodiesel (WGBD), WGO with permanent magnet (PM), electromagnet (EM) and the combination of PM and EM-based fuel ionization system and finally WGO with hydrogen induction rates of 2%, 4.3%, 6.7% and 10.3% at maximum engine load condition. It is observed that all the techniques improved the performance of WGO. Among the techniques tested, hydrogen induction displayed better results in terms of performance and emission characteristics with a slight penalty in NO emission.     

On the numerical solution of generalized convection heat transfer problems via the method of proper closure equations – part II: Application to test problems

ABSTRACT

In part I of this paper, a new physical-based computational approach for the solution of convection heat transfer problems on co-located non-orthogonal grids in the context of an element-based finite volume method was discussed. The test problems are presented here, in part II of the paper. These problems include five steady two-dimensional convection heat transfer problems. In all test cases, the convergence history, the required under-relaxations for the iterative solution of the linearized equations, and the order of accuracy of the method are discussed and the streamlines as well as isotherms are presented. The computational results show that the proposed method is second order accurate and might occasionally need mild under-relaxation in relatively complex problems. Excellent match between the computational results and the corresponding reliable published results is observed.