Correlations of vaporization performance of conventional and biofuel sprays in a crossflow heated chamber

Pre-vaporization and pre-mixing are the two main features of LPP type of combustor that operate on liquid fuels. The pre-vaporization length scale is one of its most important design parameters. In this study, the goal is to put forward a simulation based correlation for fuel vaporization performance as a function of dimensionless parameters for crossflow type of injections. Two types of fuels are studied here: jet-A and one of its potential biofuel substitutes, RME. Different sets of spray simulations are considered for crossflow type of injections. Correlations are provided for both jet-A and RME's vaporization performance as a function of non-dimensional inlet air temperature, fuel/air momentum flux ratio and normalized spray traverse distance.     

Carbon dioxide emission rates for conventional and synthetic fuels

With rising concern about the increasing atmospheric concentration of CO₂ and its potential impact on global climate, there have been suggestions that the CO₂ emission rates be considered in selecting among fuel-producing technologies. Many previous comparisons have been inadequately drawn. We discuss criteria for carefully drawn comparisons and compute CO₂ emission rates in kgC/10⁹ joules for a variety of conventional or synthetic fuel processes. Although the total CO₂ release per joule is on the order of 1.8 (±0.2) times as much for burning liquid fuels from coal as for liquid fuels from crude oil, useful comparisons among synthetic fuel processes are not easy and the results are subject to changes in boundary conditions of resource availability, plant location, environmental requirements, output slate desired, economics, etc.     

Critical analysis on hydrogen as an alternative to fossil fuels and biofuels for vehicles in Europe

In recent times, the global debate on the environment has been centered on CO₂ emissions. This gas is the major cause of the “greenhouse effect” and people are more concerned with the idea that the emissions of this gas should be minimized. As a result of this concern, the Kyoto Protocol was enacted and subscribed to by many countries, setting the maximum gas emissions for them.Fossil fuels are a major source of CO₂ emissions. For some years now The European Union has been seeking to promote some years now the use of biofuels as substitutes for diesel or petrol for transport purposes. As a result of this policy, in 2003 the European Union (EU) Directive 2003/30/EC [1] was developed with the aim of promoting the use of biofuels as a substitute for diesel or gasoline among European Union countries as well as to contribute to fulfilling the commitments acquired on climate change, security of supply in environmentally friendly conditions and the promotion of renewable energy sources.In order to achieve these goals, the directive forces all EU members to ensure that before December 31 of 2010 at least 5.75% of all gasoline and diesel fuels sold for transport purposes are biofuels. European Union countries have social and economic characteristics unique to themselves. The energy dependence on foreign sources, the features of the agricultural sector or the degree of industrialization varies greatly from one country to another. In this context, it is questionable whether the obligation imposed by this directive is actually achieving in its application uniform and/or identical goals in each of the countries involved and whether the actions of the various governments are also aligned with these goals. All these ideas were developed in a previous report (Sobrino and Monroy (2009) [2]).This report examines the possibility of using hydrogen as an alternative to fossil fuels and biofuels from a technical, economic and environmental point of view in the specific case of a European Union country: Spain.     

Life cycle assessment of conventional and optimised Jatropha biodiesel fuels

The environmental benefits and energy savings of the production of Jatropha fuels and operation in a typical LPV in India were examined. A baseline scenario and alternative optimised routes were assessed, considering different pathways of energy recovery from Jatropha coproducts. The following impact categories were assessed: Non-Renewable Energy (NRE) consumption, Global Warming Potential (GWP), Terrestrial Acidification Potential (TAP) and Respiratory Inorganic Effects (RIE). At present, the life cycle impact of Jatropha production and use is competitive with conventional diesel in terms of NRE and GHG emissions; however it results in higher local environmental impacts (RIE and TAP categories). Under optimised farming and processing practices and recovery of Jatropha coproducts either via co-generation, gasification or FT-diesel synthesis routes, Jatropha fuels reduce the impact of NRE, GHG, and RIE. The energy recovery paths to generate surplus electricity through generation and gasification routes show a better performance than FT-diesel synthesis routes in terms of NRE and GWP impacts. Nevertheless, in terms of local air pollution indicators, the FT-diesel synthesis route reveals the lowest emissions.     

The substitutive effect of biofuels on fossil fuels in the lower and higher crude oil price periods

Various biofuels, including bioethanol and biodiesel are technologically being considered replacements for fossil fuels, such as the conventional gasoline and diesel. This paper aims to measure whether economic substitutability can be generated during periods of higher and/or lower prices of crude oil. The empirical results of the bivariate EGARCH model prove that this substitutive effect was occurred during the higher crude oil price period due to the significant price spillover effects from crude oil futures to corn and soybean futures, indicating that the increase in food prices can be attributed to more consumption of biofuels. We suggest more extensive research in the search for fuel alternatives from inedible feedstock such as pongamia, jojoba, jatropha, especially the 2nd generation biofuel technologies such as algae-based biofuels.     

A comparative life cycle assessment of bio‐ and conventional fuels in a Canadian province

In this paper, a comprehensive study on corn‐based ethanol in a Canadian context is conducted, which uses the most reliable and up to date data, considers realistic assumptions, and applies sound methodology to provide a basis for developing future scenarios for corn‐based ethanol and compared the results with the conventional fuel, such as gasoline. It is estimated that the net energy value (NEV), defined as the energy content of a liter of ethanol minus the total energy use to produce a liter of ethanol, is 9.6 MJ L^?1 (LHV), when co‐products energy credits are not considered. In addition, a comparison of life cycle energy use for corn‐based ethanol and gasoline reveals that the life cycle energy use to produce a liter of ethanol is considerably less than the life cycle energy use to produce a liter of gasoline. Furthermore, a comparison of life cycle greenhouse gas (GHG) emissions for corn‐based ethanol and gasoline reveals that the life cycle GHG emissions released per liter of ethanol produced is an order of magnitude lesser than the life cycle GHG emissions released per liter of gasoline produced, when GHG emissions displaced by ethanol co‐products are considered in the estimation. Finally, a comparison of our results in terms of net fossil fuel input, net fossil fuel ratio and GHG emissions is carried out with the results obtained from the ERG biofuel analysis meta‐model (EBAMM) to reflect both Canadian and US perspectives. Copyright © 2010 John Wiley & Sons, Ltd.     

Vaporization and collision modeling of liquid fuel sprays in a co-axial fuel and air pre-mixer

Droplet collision occurs frequently in regions where the droplet number density is high. Even for Lean Premixed and Pre-vaporized (LPP) liquid sprays, the collision effects can be very high on the droplet size distributions, which will in turn affect the droplet vaporization process. Hence, in conjunction with vaporization modeling, collision modeling for such spray systems is also essential. The standard O’Rourke’s collision model, usually implemented in CFD codes, tends to generate unphysical numerical artifact when simulations are performed on Cartesian grid and the results are not grid independent. Thus, a new collision modeling approach based on no-time-counter method (NTC) proposed by Schmidt and Rutland is implemented to replace O’Rourke’s collision algorithm to solve a spray injection problem in a cylindrical coflow premixer. The so called “four-leaf clover” numerical artifacts are eliminated by the new collision algorithm and results from a diesel spray show very good grid independence. Next, the dispersion and vaporization processes for liquid fuel sprays are simulated in a coflow premixer. Two liquid fuels under investigation are jet-A and Rapeseed Methyl Esters (RME). Results show very good grid independence in terms of SMD distribution, droplet number distribution and fuel vapor mass flow rate. A baseline test is first established with a spray cone angle of 90° and injection velocity of 3 m/s and jet-A achieves much better vaporization performance than RME due to its higher vapor pressure. To improve the vaporization performance for both fuels, a series of simulations have been done at several different combinations of spray cone angle and injection velocity. At relatively low spray cone angle and injection velocity, the collision effect on the average droplet size and the vaporization performance are very high due to relatively high coalescence rate induced by droplet collisions. Thus, at higher spray cone angle and injection velocity, the results expectedly show improvement in fuel vaporization performance since smaller droplet has a higher vaporization rate. The vaporization performance and the level of homogeneity of fuel–air mixture can be significantly improved when the dispersion level is high, which can be achieved by increasing the spray cone angle and injection velocity.     

Utilizing preferential vaporization to enhance the stability of spray combustion for high water content fuels

In a previous study on the stability of spray combustion for mixtures of alcohols (ethanol or 1-propanol) and water, the feasibility of burning fuels heavily diluted with water was demonstrated. In that study it was found that the preferential vaporization of alcohols in water can significantly enhance flame stability. Due to their high volatility and high activity coefficient in aqueous solution, the alcohols quickly evaporate from the droplets and generate a concentrated fuel vapor at the base of the jet. Therefore, a flame can be ignited and stabilize even though the water content of the fuel is quite high (up to 90 wt%) (Yi and Axelbaum, 2013). In this study, we develop a procedure for selecting chemical fuels showing strong preferential vaporization in water. t-Butanol was identified as an excellent candidate based on its physical and chemical properties, including activity coefficient, vapor pressure, heat of vaporization and heat of combustion. Flame stability was evaluated for aqueous solutions of both ethanol and t-butanol using a spray burner where the extent of swirl was adjustable. Under both high and low swirl intensity, the flame stability of t-butanol aqueous solutions was better than that of ethanol. The characteristic time for fuel release from a droplet was modeled for both ethanol and t-butanol. The time to release 99% of the fuel from the droplet for t-butanol is over 70% shorter compared to that for ethanol, which supports the improved flame stability observed for t-butanol in the experiments.     

Comparing prospective hydrogen pathways with conventional fuels and grid electricity in India through well-to-tank assessment

The present study uses Greenhouse Gases, Regulated Emissions, and Energy Use in Technologies Model (GREET), to compare hydrogen generated via multiple pathways (Natural gas, methanol reforming; coal, petcoke, biomass gasification etc) with the conventional fuels like diesel and compressed natural gas and grid electricity under Indian context through a comprehensive well to tank assessment based on net CO₂ equivalent emission and energy consumption. Limited availability of customized studies comparing hydrogen production and supply with other energy options in India distinguishes the present work as it provides a fresh insight into potential pathways for hydrogen production while assessing feedstock availability and raw water consumption. The study reveals that biomass gasification and solar electrolysis are among the least GHG emitting pathways to fill one unit of energy equivalent in the tank. Hydrogen produced through natural gas reforming is 70% less emission intensive and 38% more energy efficient than Indian grid electricity.     

Dispersion and burning behavior of hydrogen released in a full-scale residential garage in the presence and absence of conventional automobiles

Experiments are described in which hydrogen was released at the center of the floor of a real-scale enclosure having dimensions of a typical two-car residential garage. Real-time hydrogen concentrations were monitored at a number of locations. The hydrogen/air mixtures were ignited at pre-determined local volume fractions ranging from 8% to 29%. The combustion behavior and structural effects were monitored using combinations of high-speed pressure transducers and ionization gauges, standard thermocouples, hydrogen sensors, and digital, infrared, and high-speed video cameras. Experiments were performed both for empty garages and garages with conventional automobiles parked above the hydrogen release location.     

Time-dependent opportunities in energy business: A comparative study of locally available renewable and conventional fuels

This work investigates and compares energy-related, private business strategies, potentially interesting for investors willing to exploit either local biomass sources or strategic conventional fuels. Two distinct fuels and related power-production technologies are compared as a case study, in terms of economic efficiency: the biomass of cotton stalks and the natural gas. The carbon capture and storage option are also investigated for power plants based on both fuel types. The model used in this study investigates important economic aspects using a “real options” method instead of traditional Discounted Cash Flow techniques, as it might handle in a more effective way the problems arising from the stochastic nature of significant cash flow contributors’ evolution like electricity, fuel and CO₂ allowance prices. The capital costs have also a functional relationship with time, thus providing an additional reason for implementing “real options” as well as the learning-curves technique. The methodology as well as the results presented in this work, may lead to interesting conclusions and affect potential private investment strategies and future decision making. This study indicates that both technologies lead to positive investment yields, with the natural gas being more profitable for the case study examined, while the carbon capture and storage does not seem to be cost efficient with the current CO₂ allowance prices. Furthermore, low interest rates might encourage potential investors to wait before actualising their business plans while higher interest rates favor immediate investment decisions.     

Life cycle assessment of hydrogen-based electricity generation in place of conventional fuels for residential buildings

In the current study, environmental impact evaluation of electricity generation from hydrogen instead of conventional fuels is investigated with a life cycle impact assessment for residential usage. For this purpose, lignite, natural gas, and hydrogen are utilized to a power plant to generate electricity in Istanbul, Turkey throughout the year. The utilized method for life cycle analysis is the CML 2001 which considers the impacts of global warming, acidification, abiotic fossil depletion, photochemical ozone creation, ionising radiation, human toxicity potential, land use, eutrophication potential, ozone layer depletion, freshwater aquatic ecotoxicity, ecotoxicity of marine aquatic, ecotoxicity of marine sediment, and terrestrial ecotoxicity. The results of the present study illustrate that the generation with hydrogen is the best option for the environment in terms of all impact category. The global warming potentials with the 500 years time horizon for each option of electricity generation are found as 1.4 × 10⁶ ton CO₂ eq, 6 × 10⁵ ton CO₂ eq and 4.6 × 10⁴ ton CO₂ eq, respectively in the month of January.     

Gas Flow in a Stratified Porous Medium with Crossflow

IntroductionMany ..servoirs are stratified in nature due to thevarying energy level of the original depositionaIenvironment. The transporting medium softs the sourcematerial depositing one layer at a time in any givenenvironment. When the depositionaI energy levelschange, the subsequent overiying layers may be differentin composition and texture, fOrming a series of dissindlarunits of strata. Such fOrmations are calIed multilayersystems. In many cases some of the layers have such lowpermeab…     

Fostering citizen deliberations on the social acceptability of renewable fuels policy: The case of advanced lignocellulosic biofuels in Canada

It is widely recognized that a lack of social acceptance is likely to hinder the ability of governments to achieve policy targets concerning renewable energies. In this paper, we discuss the results of a pre- and post-test online survey that was conducted as part of the 2012 “Advanced Biofuels” deliberative democracy public engagement event in Montréal, Québec. The event sough to foster public learning and discussion in order to produce socially acceptable policy input for one type of renewable energy: advanced lignocellulosic biofuels. Survey results show that the majority of participants were strongly supportive of advanced lignocellulosic biofuel development in Canada after the deliberative event. By the end of the event, support also grew for current Canadian biofuel policies and many agreed that increasing biofuel production should be widely supported by the Canadian public. However, despite this support, about two thirds of participants revealed that they did not feel included in government decisions about biofuels. The gap between support after inclusive deliberation and expressed exclusion from Canadian government decisions points to the importance of fostering future citizen engagements in this area of renewable energy policy.     

Heat transfer from a rotating disk in a parallel air crossflow

The heat transfer from a rotating disk in an air stream parallel to the plane of rotation is of importance in the assessment of disk brake performance. Numerically determined heat transfer coefficients and correlations are accordingly presented for a large range of rotational and crossflow velocities. These were obtained by means of large-eddy-simulations (LES). The extreme conditions of a stationary disk in an air crossflow and a rotating disk in still air are also considered. It is found that a critical ratio between the rotational and the crossflow Reynolds numbers exists with respect to rotational heat transfer augmentation. Only above this critical value, rotational heat transfer augmentation sets on in case of laminar crossflow Reynolds numbers. This phenomenon is directly linked to a flow instability that leads to a periodic vortex generation, and which can be described by the classical Landau model. For higher angular velocities, the wake becomes fully turbulent, and the transition is very rapid.     

Progress and recent trends in biofuels

In this paper, the modern biomass-based transportation fuels such as fuels from Fischer–Tropsch synthesis, bioethanol, fatty acid (m)ethylester, biomethanol, and biohydrogen are briefly reviewed. Here, the term biofuel is referred to as liquid or gaseous fuels for the transport sector that are predominantly produced from biomass. There are several reasons for bio-fuels to be considered as relevant technologies by both developing and industrialized countries. They include energy security reasons, environmental concerns, foreign exchange savings, and socioeconomic issues related to the rural sector. The term modern biomass is generally used to describe the traditional biomass use through the efficient and clean combustion technologies and sustained supply of biomass resources, environmentally sound and competitive fuels, heat and electricity using modern conversion technologies. Modern biomass can be used for the generation of electricity and heat. Bioethanol and biodiesel as well as diesel produced from biomass by Fischer–Tropsch synthesis are the most modern biomass-based transportation fuels. Bio-ethanol is a petrol additive/substitute. It is possible that wood, straw and even household wastes may be economically converted to bio-ethanol. Bio-ethanol is derived from alcoholic fermentation of sucrose or simple sugars, which are produced from biomass by hydrolysis process. Currently crops generating starch, sugar or oil are the basis for transport fuel production. There has been renewed interest in the use of vegetable oils for making biodiesel due to its less polluting and renewable nature as against the conventional petroleum diesel fuel. Biodiesel is a renewable replacement to petroleum-based diesel. Biomass energy conversion facilities are important for obtaining bio-oil. Pyrolysis is the most important process among the thermal conversion processes of biomass. Brief summaries of the basic concepts involved in the thermochemical conversions of biomass fuels are presented. The percentage share of biomass was 62.1% of the total renewable energy sources in 1995. The reduction of greenhouse gases pollution is the main advantage of utilizing biomass energy.     

Dispersion and flow properties of charcoal oil slurries (ChOS) as potential renewable industrial liquid fuels

This work reports on a preliminary study aimed at developing an industrial liquid fuel derived from charcoal and vegetable oil. Its relevance relies on the high energy potential of charcoal, its renewable nature, storage and transportation capacity in liquid form, as well as on the economic and environmental advantages derived thereof. The ability of a commercially available charcoal to be dispersed in three different organic solvents was assessed through the rheological characterisation of the resulting charcoal oil slurries (ChOS). The charcoal was ground in a conventional ball mill and dispersed with the aid of three different surfactants. The effects of the most relevant factors influencing the rheological properties of the suspensions were evaluated, including: (i) the solvent producing the lowest fuel viscosity (η) at a given charcoal content; (ii) the most efficient surfactant (and its amount) minimising the fuel viscosity (η) at a given solids fraction; and (iii) the charcoal content, which should be as high as possible. High-stability ChOS containing 62 wt% solids and 0.4 wt% surfactant, and exhibiting adequate flow properties and high calorific values, were successfully obtained.     

Transient Performances of a Two—Pass Gas—to—Gas Crossflow Heat Exchanger

INTaoDUCTIoNThecrossllowgas-trtasheatexchngehasbeenwidelyusedinmanengineeringfields,suchastheenvironmDtalcontrosystemofaeroplanes.Itstransientbehaviourshavebecomemoreandmorebopor-ta-nttothedesignandtheperformanceofthewholesystem.Theinvestigationofthetransielltbehavioursisthefocusoftoday'sresearches.Bothnumericalll]andanalyticalmethodsl2]havebeenusedforthispurpose.Thenumericalmethodismoregenerala-ndcanbeusedfordifferentkindsofheatexchangersandworkingconditions,butitiscomplicatedandmoredriei…