Giancarlo Sorrentino

Pyrolitic and Oxidative Structures in Hot Oxidant Diluted Oxidant (HODO) MILD Combustion

The typical reactive structure stabilized in a diffusion layer in standard conditions can be significantly modified whether injected flows are diluted and/or preheated. The flow high initial enthalpy and the low fuel and/or oxygen concentration can drastically modify the structure of the oxidative and pyrolytic region due to change of the physical and chemical kinetics respect to conventional diffusion flame. Such operative conditions are typical of MILD (Moderate or Intense Low-oxygen Dilution)combustion processes. The effect of inlet conditions on the stabilized reactive structure has been studied by analyzing the behavior of a steady, one-dimensional diffusive layer. The change of the structures of the reactive region induced by a hot oxidant and diluted oxidant flow (HODO) fed towards a fuel jet at environmental temperature was numerically analyzed by means of temperature and heat release profiles, that are key parameters to understand the main features of the reactive region. In addition, the effect of diluent nature was studied by comparing the reactive structures also obtained with steam and carbon dioxide.

Thermal and mechanical stabilization process of the organic fraction of the municipal solid waste

In the present study a thermo-mechanical treatment for the disposal of the Organic Fraction of Municipal Solid Waste (OFMSW) at apartment or condominium scale is proposed. The process presents several advantages allowing to perform a significant volume and moisture reduction of the produced waste at domestic scale thus producing a material with an increased storability and improved characteristics (e.g. calorific value) that make it available for further alternative uses. The assessment of the applicability of the proposed waste pretreatment in a new scheme of waste management system requires several research steps involving different competences and application scales. In this context, a preliminary study is needed targeting to the evaluation and minimization of the energy consumption associated to the process. To this aim, in the present paper, two configurations of a domestic appliance prototype have been presented and the effect of some operating variables has been investigated in order to select the proper configuration and the best set of operating conditions capable to minimize the duration and the energy consumption of the process. The performances of the prototype have been also tested on three model mixtures representing a possible daily domestic waste and compared with an existing commercially available appliance. The results obtained show that a daily application of the process is feasible given the short treatment time required and the energy consumption comparable to the one of the common domestic appliances. Finally, the evaluation of the energy recovered in the final product per unit weight of raw material shows that in most cases it is comparable to the energy required from the treatment.

Generation of a Test Reference Year (TRY): An Application to the Town of Palermo

The improvement of the energy efficiency of buildings calls for the availability of tools for evaluating and simulating the thermal behaviour of buildings, needing as input climatic databases. These databases contain a very large amount of data, resulting in long computational time analysis. Therefore, simple aggregation methods are used, among which the test reference year (TRY). In this paper, a comparison between two statistical methodologies for compiling a TRY, the Belgian and the Sandia methods, is presented. Then, the two methods have been utilized for compiling the TRY for the town of Palermo, Italy, and compared both statistically and by means of two simple applications, obtaining quite different results. Thus, a particular caution in the choice of the method for generating such reduced sets of data is suggested.

Numerical investigation of the ignition and annihilation of CH4/N2/O2 mixtures under MILD operative conditions with detailed chemistry

The identification of controlling processes on the micro-scale level is critical in the elaboration of effective models with particular regard to MILD (moderate or intense low-oxygen dilution) combustion modelling. The objective of this study is to determine relevant features and controlling mechanisms in the ignition, interference and annihilation of diffusion layers in MILD combustion conditions. The two interfaces between the mixing layers are sufficiently close to cause interference phenomena. The inner region between the two interfaces is assumed to be air to mimic the engulfed air in a fuel jet. The temporal evolution has been analysed in dependence on the initial oxidant layer width and temperature; evidencing possible interactions between the two mixing layers. Interactions can be categorised according to the ignition and annihilation stages. Concerning the ignition, the minimum ignition delay for interfering double diffusive layers is significantly shorter than the corresponding isolated one. However, the ignition exhibits the same most reactive mixture fraction, and the ignition delay dependence on the oxidant layer width behaves similar to a stratified charge condition for the same most reactive mixture fraction. In the ignition region, the scalar dissipation rate is reduced due to expansion toward fuel sides due to heat release. The annihilation time delay scales with the initial layer thickness according to the canonical diffusion equation and does not significantly depend on the initial oxidant temperature. Oxygen depletion during annihilation limits oxidation in the rich side mixture, which produces a final oxidation level near equilibrium values.

Role of Green Coverings in Mitigating Heat Island Effects: An Analysis of Physical Models

Worldwide, governments are introducing several rules and standards in the aim of limiting the quantity of primary energy for air conditioning of buildings and supporting the use of renewable source of energy for generating thermal and electric energy to be utilized in buildings such as the European Directive on the Energy Performance of Buildings [1]. Along with these interventions, another important action takes currently place in the building sector, that is the introduction of passive structural components of the envelope, able to reduce the requirements of energy for air conditioning purposes. Among these building components, the so-called green roofs are becoming more and more interesting for designer and buildings owners. This simple technical solution, in fact, apart its effectiveness in lowering particularly the summer cooling loads, could make more attractive the shape of each single building and, when adopted on a large extension, of an entire city district, reducing the risks for urban heat island phenomena that represent a severe problem in urban contexts. In this work, a short review of the literature models for computing the energy balance of roof coverings will be proposed, with particular reference in modelling the heat exchange of a canopy.

Distributed combustion in a cyclonic burner

Distributed combustion regime occurs in several combustion technologies were efficient and environmentally cleaner energy conversion are primary tasks. For such technologies (MILD, LTC, etc…), working temperatures are enough low to boost the formation of several classes of pollutants, such as NOx and soot. To access this temperature range, a significant dilution as well as preheating of reactants is required. Such conditions are usually achieved by a strong recirculation of exhaust gases that simultaneously dilute and pre-heat the fresh reactants. However, the intersection of low combustion temperatures and highly diluted mixtures with intense pre-heating alters the evolution of the combustion process with respect to traditional flames, leading to significant features such as uniformity and distributed ignition. The present study numerically characterized the turbulence-chemistry and combustion regimes of propane/oxygen mixtures, highly diluted in nitrogen, at atmospheric pressure, in a cyclonic combustor under MILD Combustion operating conditions. The velocity and mixing fields were obtained using CFD with focus on mean and fluctuating quantities. The flow-field information helped differentiate between the impact of turbulence levels and dilution ones. The integral length scale along with the fluctuating velocity is critical to determine Damkohler and Karlovitz numbers. Together these numbers identify the combustion regime at which the combustor is operating. This information clearly distinguishes between conventional flames and distributed combustion. The results revealed that major controllers of the reaction regime are dilution and mixing levels; both are significantly impacted by lowering oxygen concentration through entrainment of hot reactive species from within the combustor, which is important in distributed combustion. Understanding the controlling factors of distributed regime is critical for the development and deployment of these novel combustion technologies for near zero emissions from high intensity combustors and energy savings using fossil and biofuels for sustainable energy conversion.Distributed combustion regime occurs in several combustion technologies were efficient and environmentally cleaner energy conversion are primary tasks. For such technologies (MILD, LTC, etc…), working temperatures are enough low to boost the formation of several classes of pollutants, such as NOx and soot. To access this temperature range, a significant dilution as well as preheating of reactants is required. Such conditions are usually achieved by a strong recirculation of exhaust gases that simultaneously dilute and pre-heat the fresh reactants. However, the intersection of low combustion temperatures and highly diluted mixtures with intense pre-heating alters the evolution of the combustion process with respect to traditional flames, leading to significant features such as uniformity and distributed ignition. The present study numerically characterized the turbulence-chemistry and combustion regimes of propane/oxygen mixtures, highly diluted in nitrogen, at atmospheric pressure, in a cyclonic combustor...