J. Porteiro

Development of a Predictive CFD Fouling Model for Diesel Engine Exhaust Gas Systems

This article presents a numerical simulation procedure for studying soot particle deposition in diesel exhaust systems, with a particular focus on fouling layer thickness evolution. In the proposed algorithm, particle transport toward the wall, adhesion, and reentrainment of particles from the surface have been modeled, including Brownian motion and turbulent diffusion, thermophoresis, adhesion, and removal. This model has been implemented in ANSYS Fluent, which makes the inclusion of local effects possible. A cross-flow device, with a tube positioned transverse to the flow, has been simulated and tested. A comparison of the predicted fouling layer at several angular positions with the experimental observation shows acceptable agreement. This model makes it possible to predict the real depth of the fouling layer and its effects on the hydrodynamics of the flow. This model represents a valuable tool for the prediction of the main aspects of the performance of heat exchangers exposed to fouling.

A Refrigerated Web Camera for Photogrammetric Video Measurement inside Biomass Boilers and Combustion Analysis

This paper describes a prototype instrumentation system for photogrammetric measuring of bed and ash layers, as well as for flying particle detection and pursuit using a single device (CCD) web camera. The system was designed to obtain images of the combustion process in the interior of a domestic boiler. It includes a cooling system, needed because of the high temperatures in the combustion chamber of the boiler. The cooling system was designed using CFD simulations to ensure effectiveness. This method allows more complete and real-time monitoring of the combustion process taking place inside a boiler. The information gained from this system may facilitate the optimisation of boiler processes.

Combustion Behavior of Spanish Lignocellulosic Briquettes

If briquettes are to be used efficiently and rationally as fuel, they must be characterized to determine such technological parameters as their reactivity, moisture content, density, ashes, volatile matter, and heat value, along with their major component elements. Traditionally, research has centered on small particles of coal that do not reflect the combustion behavior of briquettes as heterogeneous solids. The objective of this work is to compare experimental data on the reactivity of biomass briquettes and to analyze the results. From the reactivity and the rest of the data available, it will be possible to asses what kind of briquette is suitable for a particular application by matching its behavior to specific requirements, including pollutant emissions.

On the Behavior of Different PCMs in a Hot Water Storage Tank against Thermal Demands

Advantages, such as thermal storage improvement, are found when using PCMs (Phase Change Materials) in storage tanks. The inclusion of three different types of materials in a 60 𝓁 test tank is studied. Two test methodologies were developed, and four tests were performed following each methodology. A thermal analysis is performed to check the thermal properties of each PCM. The distributions of the water temperatures inside the test tanks are evaluated by installing four Pt-100 sensors at different heights. A temperature recovery is observed after exposing the test tank to an energy demand. An energetic analysis that takes into account the energy due to the water temperature, the energy due to the PCM and the thermal loss to the ambient environment is also presented. The percentage of each PCM that remains in the liquid state after the energy demand is obtained.

CFD analysis of a TG–DSC apparatus : Application to the indium heating and phase change process

A ThermoGravimetric analyser with differential scanning calorimetry (TG–DSC) has been studied during the fusion of an indium sample using both an experimental procedure and a CFD simulation. To do so, a CAD model of the real device was built and meshed in detail, in order to take into account the small scale processes which occur inside the crucibles. Several theoretical models, some previously existing in the CFD software used and others developed ad hoc, were applied to simulate the whole facility. Therefore, realistic boundary conditions and a PID-based control system already developed for previous studies had to be used. The validation of the CFD model was done by comparing the outcome of the resulting simulation to the results obtained by experimental procedure in a case where natural convection is the main heat and mass transfer mechanism. This comparison was made for two different heating rates inside the furnace. Typical characteristics of phase change process inside a TG-DSC as thermal lag, onset temperature or heat flow exchange during the fusion could be analysed. As well, a more detailed approach to physical phenomena taking place inside the furnace could be done, since CFD simulations allow to obtain data which is not achievable experimentally. Besides, a valid CFD model for a TG-DSC could be later used in further CFD simulations.

Exhaust Emissions from Diesel, LPG, and Gasoline Low-power Engines

Abstract In a way similar to the automotive industry, outboard emissions limits are being constantly revised, which strongly effects the development of the new engines and their compliance. During the last ten years, conventional two-stroke outboard engines, which are used for fishing and recreational boats, have thus been replaced by four-stroke engines or direct-injection two-stroke engines. The objective of this article is to compare various outboard engines and the technical solutions developed for the reduction of exhaust emissions, with special emphasis being placed on the low-power gasoline and diesel outboard engine range. A gasoline outboard engine was also transformed to allow the use of liquefied petroleum gas (LPG) and showed that this technique could be an alternative solution for the future emission limit compliance.

Contribution of Renewable Energy Sources to Electricity Production in Galicia (Spain)

The use of renewable energy offers a decrease in external energy dependence; a boost to local and regional component manufacturing industries; promotion of regional engineering; increased R&D, decrease in impact of electricity production and transformation; increase in the level of services for the rural population; creation of employment, etc. To achieve these benefits, a series of actions are required, among which the following are particularly important: creation of a suitable climate for performing R&D; training of technicians in design, production, and maintenance of equipment; motivation for establishing a new market; proper financing; fostering of appropriate technologies; practical demonstration of results; etc. This article reviews the progress made in the Autonomous Community of Galicia in terms of the introduction of renewable energy technologies (RETs) and examines the possibility of meeting a target of 90% coverage (practical electrical self-sufficiency) by 2010.

Effect of Different Configurations on Small Pellet Combustion Systems

The combustion of pellets in small stoves is a complex issue in which many factors must be considered. The University of Vigo has developed a 24 kWt fixed bed stove pilot plant for studying pellet combustion in which different configurations and operational conditions can be tested. An extensive experimental study using the statistical analysis approach is presented. Analyses of the main control factors involved in the performance of stoves of this kind and their optimization are also presented, including preheating of air, secondary air supply and gas recirculation. The influence of air and pellet feeding rates and stove temperature as part of a group of energy and environmental variables is analyzed in detail. The study establishes that the use of secondary air and, especially, the recirculation of gases considerably reduce CO emissions.

Experimental analysis of several biomass fuels: The effect of the devolatilization rate on packed bed combustion

An experimental analysis of the ignition front propagation of eight biomass fuels in a one-dimensional fixed-bed combustor (batch reactor) is carried out and these biomass materials are also researched by thermogravimetry to study their thermal behaviour during devolatilization. The analysis of the thermogravimetric data has been centered on the results obtained for 50 °C · min−1 (maximun heating rate of the thermogravimetric (TG) equipment), taking into consideration that it is the nearest heating rate value to the one at which the heating process is carried out in the batch reactor. The influence of the TG-determined devolatilization rate in the burning behaviour of biomass in situations of packed bed combustion is analyzed. This study reveals that the biomass fuels with higher devolatilization rates during pyrolysis are the ones with a higher velocity of propagation of the ignition front during combustion processes in the fixed-bed combustor. The thermal decomposition characteristics during devolatiliz...

On the Application of Image Processing Methods for Bubble Recognition to the Study of Subcooled Flow Boiling of Water in Rectangular Channels

This work introduces the use of machine vision in the massive bubble recognition process, which supports the validation of boiling models involving bubble dynamics, as well as nucleation frequency, active site density and size of the bubbles. The two algorithms presented are meant to be run employing quite standard images of the bubbling process, recorded in general-purpose boiling facilities. The recognition routines are easily adaptable to other facilities if a minimum number of precautions are taken in the setup and in the treatment of the information. Both the side and front projections of subcooled flow-boiling phenomenon over a plain plate are covered. Once all of the intended bubbles have been located in space and time, the proper post-process of the recorded data become capable of tracking each of the recognized bubbles, sketching their trajectories and size evolution, locating the nucleation sites, computing their diameters, and so on. After validating the algorithm’s output against the human eye and data from other researchers, machine vision systems have been demonstrated to be a very valuable option to successfully perform the recognition process, even though the optical analysis of bubbles has not been set as the main goal of the experimental facility.