• Energy Research

Experimental and computational activities were performed to determine the possible improvements of total environmental impact of a wood-open fireplace. Two models of fireplaces will be discussed, both with the same power and with only a difference relative to the geometry of the internal elements of the heat exchanger. In the second model the two blades have been substituted with one pipe that represents a possible and cheaper solution in the way of optimization. The optimization process has been conducted up to the determination of a third configuration with a better thermal efficiency. While combustion emissions are difficult to reduce where only a minimum control of actual combustion conditions can be ensured in such domestic appliances, a significant improvement can be considered for the heat recover efficiency. This improvement can be achieved through a detailed analysis of the thermal conditions realized and can require modifications to the heat exchanger geometry profitable from the manufacturing point of view too. © 2006 Elsevier Inc. All rights reserved.

Pressure swirl sprays are frequently used in burners for gas turbines like the LPP chamber or to generate diffusion flames. Combustion between fuel and the air is governed by complex phenomena determined by the mixing of the mass flow rate of the two phases liquid and gaseous. Characterization of the spray by measuring the half cone angle fluctuations with a speed camera and a Lagrangian approach allows the working space of the spray to be defined and the "signature" of the spray in well-defined conditions of supply pressure to be identified. The results define the pseudo-chaotic structure of the spray and highlight behavior affecting the combustion process.

Energy transition strongly leads researcher to find short-term alternative carbon-free fuelsto be used in internal combustion engines. An interesting and transient solution can be thedual fuel (DF) technology. It can offer significant reduction of carbon dioxide and pollutantemissions. In this paper, DF operation was performed in an optically accessed researchdiesel engine running at a constant speed of 1500 rpm. Substitute fuels (methane orhydrogen) were injected in the intake manifold in front of the entrance of the tumbleintake port. The objective was to compare the two DF modes using simultaneously Fast UVeVisible and Fast Infrared (IR) Imaging. We observed that IR camera was able to give deepercombustion information and allowed to grab the whole phenomenon for both DF hydrogenand methane, while identifying the combustion starting points. Also, IR acquisitions forpremixed hydrogen evidenced an unpredictably behaviour of the mixture, demonstratingthe necessity of a specific Diesel injection strategy to avoid hydrogen auto-ignition athigher engine load. Finally, a comparison of the measured emissions at the exhaust evidencedthat in DF mode (both with CH4 and H2) a significant reduction of particulate matteris achieved with respect to conventional diesel operation. In addition, when hydrogen isused as primary fuel, a more efficient combustion is obtained drastically reducing HC andCO2.

Micro-explosion is caused by the sudden vaporization of water drops inside water-in-oil emulsion. Past studies have shown an optimal diameter for dispersed water. This optimal micro-explosion produces the largest number of secondary droplets, i.e. the largest interfacial area among the resulting spray. Such an increase in the interfacial area within the spray causes a better and less polluting combustion process. By using an infra-red camera, the present experiments can measure the size and planar velocity of secondary droplets issued from an optimal and also a non-optimal emulsion. The distributions of kinetic energy and surface energy among the spray are then calculated and discussed. Among the secondary droplets, it results that the optimal micro-explosion favors surface energy over kinetic energy.

The performance of a domestic appliance for wood logs combustion is a function of several variables, such as the geometric design of the appliance and its operating parameters. Among them, air feeding conditions are really decisive if the objective function is the maximization of the heat recovered from flue gases. Therefore, even if pollutant emissions have to be ever considered, the amount of excess air can be seen as a fundamental parameter in the definition of thermal efficiency of the appliance. In this paper the role of this parameter is analysed. The analysis is conducted by linking the results obtained from experimental data, detailed CFD simulations and a simplified mathematical model based on a network of CSTR. The derivation of an idealized schematization of the appliance was essential to realize the role of excess air variations, with more generality than with respect to a specific appliance configuration. Conversely, while the experimental data and CFD results were necessary to derive the simplified model, the indications given by this simplified model were useful to analyze results coming from both experiments and detailed numerical simulations. It has been evidenced the need to distinguish between the role of excess air in the chemical combustion and in the heat recovery in the appliance as well as to quantify the feedback between these two processes.

fragmentation of solid fuels under severe heating conditions. The devise is a modified heated strip reactor, capable to reach 2000°C in less than 0.2s. Particles are laid on the strip and pyrolysed under inert or moderately oxidizing conditions. The char particles and their fragments, generated upon pyrolysis, can be recovered and analysed to assess the fragmentation propensity of the fuel. Some preliminary experiments have been carried out on two biomass samples in order to assess the temperature time history of particles in the experimental apparatus. In particular biomass particles of approximately 2-3 mm have been used. The temperature of the heated strip reactor in such preliminary tests was varied between 1000 and 1600°C, while the strip nominal heating rate was kept at 104°C/s and the holding time was set at the value of 10s. A near infrared fast camera (38000 frames/sec) has been used to measure the temperature of the heated strip and of the particles during the tests. A heat up model was developed and validated against experimental results. The model was then used to estimate the temperature gradients across particles of biomass and of coal as well. Results show that the strip of the reactor reaches the set temperature in less than 0.2s. When particles are laid on the strip, their bottom surface, which is in physical contact with the strip, immediately reaches the set temperature value. For 1mm coal particles the upper surface can be considered at the same temperature as well. Under the most severe conditions tested (strip temperature of 1600°C , biomass particles of 2mm thickness) the temperature difference between the bottom and the upper face is 200°C after 3s and drops to 100°C after 10 s. On the whole the experimental apparatus simulates uniform heating of the particles with reasonable approximation. In the next future the apparatus will be further upgraded to operate at pressures up to 20 bar.

Currently, due to the stringent and explicit European environmental legislation about land spreading of nitrates, the direct land application of the poultry litter (PL) is not anymore the most appropriate disposal technique [European law 1991/676/CEE]. According to the recent European guide lines concerning the smart grids, the generation of electricity and heat from poultry derived wastes based on high-temperature thermal destruction techniques, i.e. combustion, could be a promising local waste management solution. In this work we set out to investigate the technical and the economic feasibility of the combustion of poultry litter blended with olive pomace in a domestic burner (35 kW) initially designed for wood pellets. Flue gas and solid by-products during combustion tests were characterized at varying poultry litter content in the pellets. Compared to the combustion of wood pellets, CO and particulate emissions increased with PL content, whose inorganic fraction was mainly concentrated in the ashes. Under optimized conditions, the burner could be satisfactorily fuelled with pellets containing up to 50% PL by weight.