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It is conventionally believed that there are no self-sustained thermoacoustic oscillations in the absence of acoustic modes in combustors. However, such oscillations (also known as intrinsic thermoacoustic instability) are recently found to occur in a premixed combustor with a mean flow present but no acoustic eigenmodes involved. Practical combustors are associated with entropy waves, pressure jump and mean flow, which are ignored in previous studies without justification. In this work, an entropy-involved energy measure is defined and used to study the stability behaviors of intrinsic thermoacoustic modes. The concepts and methods are exemplified with the classical time-delay n–τ unsteady heat release model. The intrinsic thermoacoustic eigenmodes are found to be related to not only a flame transfer/describing function but also the acoustic impedance at the flame, which is boundary-dependent. It is shown that the predicted frequency ωfr of the intrinsic modes and the critical gain nc depend on the ratio T¯2/T¯1 between the after- and before-combustion temperatures and the inlet mean flow Mach number M¯1. Comparison is then made between the present results and those available in literature. Good agreement is obtained for ωfr. Furthermore, the predicted stability of intrinsic modes based on calculated nc is found to agree well with direct numerical simulations (DNS). It is also interesting to show that as T¯2/T¯1→1, the critical gain as predicted from the previous models is nc→+∞, which means that all intrinsic eigenmodes are stable. However, the present works shows that nc→1.0. Further illustration is then performed by conducting case studies of measured flame transfer and describing functions in premixed combustors. The present work opens up an alternative but more applicable way to study intrinsic thermoacoustic oscillations via the entropy-involved energy measure.

Metal-based fuel-borne catalysts (FBCs) have been used with diesel fuels to effectively reduce soot and diesel particulate matter (DPM) emissions from both on-road and off-road applications. However, there is a lack of detailed investigations on the potential changes in the properties of particulates, when FBCs-doped fuels are combusted in diesel engines. This study fully evaluates the potential impacts of ferrocene-doped ultralow sulfur diesel (ULSD) fuels on physical, chemical and toxicological characteristics of the particulates emitted by a single cylinder, direct-injection diesel engine working at a constant speed and at three engine loads. The results indicated that ferrocene-doped fuels could effectively reduce the particulate mass and elemental carbon (EC) emissions, while increasing the proportion of both organic carbon (OC) and water-soluble organic carbon (WSOC) in particles. Particle-phase PAHs and n-alkanes emissions increased with an increase of Fe in the fuels. Ferrocene addition also led to lower soot ignition temperature and activation energy. However, the total number emissions of particles from ferrocene-doped fuels dramatically increased due to the formation of Fe-rich nuclei mode particles. Compared to pure ULSD, the particles emitted from ferrocene-doped fuels showed a slight decline in cell viability. The Fe in the particles and the changes in chemical composition of particulates are thought to be responsible for the variation of cell viability.

Abstract This paper deals with an optimization of the Stirling engine regenerator’s. Firstly, different materials are experimented (Stainless Steel, Copper, aluminum and Monel 400). The engine performances and the state of each material after 15 h of use are considered. The Stainless steel was the material that best satisfies these two conditions. Five regenerators in stainless steel with different porosities were manufactured and experimented (95%, 90%, 85%, 80% and 75%). Porosity that gives the best trade-off between maximizing the engine brake power, maximizing the heat transfer and minimizing the pressure drops, was retained. Thus, the regenerator in stainless steel with porosity of 85% was considered as the most suitable matrix maximizing the Stirling engine performances and minimizing heat and friction losses.

Abstract The Biofuels Directive sets reference values for the quantity of biofuels and other renewable fuels to be placed on the transport market. Biogas from agricultural crops can be used to meet this directive. This paper investigates biogas production for three crop rotations: wheat, barley and sugar beet; wheat, wheat and sugar beet; wheat only. A technical and economic analysis for each crop rotation was carried out. It was found that wheat produces significantly more biogas than either barley or sugar beet, when examined on a weight basis. However sugar beet produces more biogas and subsequently more energy when examined on an area basis. When producing biofuels, land is the limiting factor to the quantity of energy that may be produced. Thus if optimising land then a crop rotation of wheat, wheat and sugar beet should be utilised, as this scenario produced the greatest quantity of energy. This scenario has a production cost of €0.90/mN3, therefore, this scenario is competitive with petrol when the price of petrol is at least €1.09/l (VAT is charged at 21%). If optimising the production costs then a crop rotation of wheat only should be utilised when the cost of grain is less than €132/ton. This scenario has the least production cost at €0.83/mN3, therefore, this scenario is competitive with petrol when the price of petrol is at least €1.00/l. But as this scenario produces the least quantity of biogas, it also produces the least quantity of energy. In comparing with other works by the authors it is shown that a biomethane system produces more energy from the same crops at a cheaper cost than an ethanol system.

Abstract This study presents a detailed kinetic investigation into ultra-rich oxidation of H 2 S-CH 4 under high temperature (900–1250 °C) and ambient pressure. Effects of temperature, initial H 2 S/CH 4 ratio and equivalence ratio (Φ) on reactants conversions and products distributions were experimentally studied in a tubular flow reactor and kinetically analyzed by CHEMKIN software. A detailed kinetic mechanism involving 85 species and 515 reactions has been developed and validated using reference data for H 2 S-CH 4 decomposition and results from extended experimental conditions involving the O 2 addition. For H 2 S-CH 4 system, conversion of H 2 S increased steady with the rising temperature while reactivity of CH 4 was weak at temperature below 1000 °C. At temperature higher than 1000 °C, conversion of CH 4 increased rapidly and devoted further formation of H 2 and CS 2 mainly via reacting with H 2 S decomposition products. The H 2 production efficiency was negatively associated with initial H 2 S fraction as H 2 S decomposition was dominant H 2 source within 1150 °C. The stoichiometric ratio for H 2 S/CH 4 merely showed its advantage in H 2 production at higher temperature under which CH 4 reached its equilibrium conversion swiftly. Introduction of little amount of O 2 (Φ = 6 or higher) accelerated the whole reaction process and triggered H 2 S partial oxidation and H 2 formation at lower temperature. CH 4 explicitly showed inferior position in oxidation competition with H 2 S and maintained poor conversion at temperature below 950 °C. The results of rate of production (ROP) analysis at condition without O 2 showed that CH 4 reactivity showed dependence on free S radical via S + CH 4 = SH + CH 3 , and the formed CH 3 was mainly converted via reacting with SH and H radicals. CH 3 could be concurrently reverted to CH 4 via reactions with H 2 S and H 2 . O 2 activated the whole system by forming chain branching radicals O and OH. These radicals promoted H 2 S and CH 4 conversions to form richer S, H and CH 3 radicals. SH + CS = CS 2 + H was important for CS 2 formation and with presence of O 2 , CS 2 was likely to be consumed via oxidation reactions. Finally reaction pathways for H 2 S, CH 4 conversion and H 2 , CS 2 formation were presented.

An electric and thermal model of the hybrid device consisting of a dye-sensitized solar cell (DSSC) and a thermoelectric generator (TEG) is studied for exploiting the solar full spectrum. Analytical expressions for the power outputs and efficiencies of the DSSC, TEG and hybrid device are derived. Temperature-dependent coefficients of the DSSC are introduced and their values being consistent with the experimental data are determined. The effects of the operating electric current, working temperature and temperature-dependent coefficient in the DSSC on the performance of the hybrid device are discussed in detail. The optimum performance characteristics of the hybrid derive at different temperature conditions and the DSSC at the reference temperature condition are compared. The parametric design criteria of the optimal coupling are given. These results obtained here may provide some guidance for the optimum design of practical hybrid devices.

Abstract The South Korean government has been actively promoting an educational-facility improvement program as part of its energy-saving efforts. This research seeks to develop a decision support model for selecting the facility expected to be effective in generating energy savings and making the facility improvement program more effective. In this research, project characteristics and electric-energy consumption data for the year 2009 were collected from 6282 elementary schools located in seven metropolitan cities in South Korea. In this research, the following were carried out: (i) a group of educational facilities was established based on electric-energy consumption, using a decision tree; (ii) a number of similar projects were retrieved from the same group of facilities, using case-based reasoning; and (iii) the accuracy of prediction was improved, using the combination of genetic algorithms, the artificial neural network, and multiple regression analysis. The results of this research can be useful for the following purposes: (i) preliminary research on the systematic and continuous management of educational facilities’ electric-energy consumption; (ii) basic research on electric-energy consumption prediction based on the project characteristics; and (iii) practical research for selecting an optimum facility that can more effectively apply an educational-facility improvement program as a decision support model.

Nanosize copper embedded in the inert carbon shell (Cu@C) prepared by carbonization of Cu2+-β-CD at 573 K was dispersed in TiO2. The Cu@C (0.1% and 0.3%) dispersed TiO2 was used in assembling of photoanodes for dye-sensitized solar cells (DSSCs). By small angle X-ray scattering (SAXS) spectroscopy, it is found that the Cu@C dispersed TiO2 having an average Cu diameter of 18.3 nm and carbon shell thickness of 3–5 nm. Larger Cu nanoparticles having an average diameter of 24.5 nm in TiO2 was formed when their carbon shells were steam reformed at 673 K. The Cu nanoparticles having a spherical shape are well dispersed in TiO2, which significantly enhance the photo-excited electron transfer for the DSSC. Notably, the Cu dispersed TiO2 photoanode has a greater efficiency than the pure TiO2 one by at least 23%. This work exemplifies a simple and novel alternative to enhance DSSC efficiencies.

Abstract A high heat storage capacity form-stable composite phase change material (CPCM) with enhanced flame retardancy that integrated modified glass fibers with form-stable PCM was proposed. The modified glass fibers were wrapped by a composite flame retardant coating. The thermal and flame retardant properties of the CPCM were measured and compared to other CPCM samples. The results of vertical burning test indicated that the glass fibers improved the mechanical properties of the CPCM and prevented it from fracturing during the burning process. The modified glass fibers could further improve the flame retardancy of CPCM, and V-0 burning rating was achieved while the content of paraffin was maintained at 70 wt%, which means the proportion of flame retardants could be reduced. TGA results showed that the modified glass fibers could enhance the thermal stability and retard the degradation process of the CPCM, and the char residue was increased to 15.3%. Thermal cycling results indicated that the CPCM has good thermal reliability. The results of cone calorimeter test indicated that the peak heat release rate (PHRR) of flame retardant form-stable CPCM dropped by 58.8%, and the combustion rate could be greatly slowed down due to the protection of carbon layers formed by modified glass fibers. In addition, the thermal conductivity of CPCMs were greatly enhanced and the CPCM has good thermal reliability.