Luca Andreassi

Modeling Carbon Monoxide Direct Oxidation in Solid Oxide Fuel Cells

In the present study, the results of the numerical implementation of a mathematical model of a planar anode-supported SOFC are reported. In particular, model results are validated and discussed when the fuel is a mixture of hydrogen and carbon monoxide, focusing on the importance of simulating direct oxidation of carbon monoxide. The mathematical model is solved in a 3D environment and the key issue is the validation comparing with experimental data, which is made in different operating conditions to establish the reliability of the presented model. The results show the importance of simulating direct oxidation of carbon monoxide and its effect on the fuel cell performance.

1D-3D Analysis of the Scavenging and Combustion Process in a Gasoline and Natural-Gas Fuelled Two-Stroke Engine

The paper presents a 1D-3D numerical model to simulate the scavenging and combustion processes in a small-size spark-ignition two-stroke engine. The engine is crankcase scavenged and can be operated with both gasoline and Natural Gas (NG). The analysis is performed with a modified version of the KIVA3V code, coupled to an in-house developed 1D model. A time-step based, two-way coupled procedure is fully described and validated against a reference test. Then, a 1D-3D simulation of the whole two-stroke engine is carried out in different operating conditions, for both gasoline and NG fuelling. Results are compared with experimental data including instantaneous pressure signals in the crankcase, in the cylinder and in the exhaust pipe. The procedure allows to characterize the scavenging process and quantify the fresh mixture short-circuiting, as well as to analyze the development of the NG combustion process for a diluted mixture, typically occurring in a two-stroke engine. Results in terms of performance and emission characteristics of this engine are presented and discussed.

Numerical-Experimental Comparison of the Performance of a Partially Stratified Charge Natural Gas Fuelled Engine

Compressed natural gas (CNG) has great potential as an alternative fuel for vehicle engines, and can reduce emissions and improve fuel economy. A single cylinder research engine has been modified to enable direct injection of a small quantity of fuel near the spark plug, independently of an overall lean homogeneous charge. Thus a partially stratified charge is formed within the chamber, which allows significant extension of the lean limit of combustion. This results in an improvement in specific fuel consumption. Numerical simulation also plays an important role in the development of such technological solutions. 3D simulations, in particular, are desirable to provide complete information about thermal and fluid dynamical fields within the chamber. In particular, among the developed numerical tools linked to the KIVA-3V code, special attention was dedicated to the formulation of the combustion model (CFM) turbulent combustion model based on the flamelet hypothesis), to adequately model non-homogeneities and lean mixture compositions. In this paper an optimization procedure is assessed, with the ultimate goal of designing combustion chambers properly devoted to be operated under lean (homogeneous and PSC) mixture conditions. The results related to the procedure definition and to its experimental validation are presented. Experimental and numerical data have been compared in terms of pressure cycles and heat release rate profiles. The overall results are encouraging, taking into special account the difficulty to reliably predict the key performance parameters without any “tuning interventions”, even when mixture richness and homogeneity were varied.Copyright

Comparing Energy and Cost Optimization in Distributed Energy Systems Management

Distributed generation, despite not being a new concept, is assuming a leading role in the field of energy conversion, as it should contribute to the enhancement of efficiency, flexibility, and reliability of national energy systems. However, it also noted that the effective performances of small and flexible power plants is critically influenced by their actual control strategy. Moreover, it is not trivial to identify a univocal parameter to evaluate the plant performance. For instance, cost evaluation clearly responds to an industrial view of the energy supply problem, while energy consumption or polluting emissions comply with a socio economic approach. In this scenario, the optimization of the plant management is a valuable instrument to gain insight on their behavior as the control strategy is varied, as well as to promote the distributed generation development, by maximizing the plants performances. In this paper, we further develop a graph based optimization methodology to optimize the set-point of an internal combustion engine based plant used to satisfy a hospital energy load, under different seasonal load conditions (winter, summer, and transitional seasons) and energy prices. Specifically, in order to dissect the effects of the objective function selection, two different optimization criteria are considered, namely economical optimization and primary energy consumption minimization. In particular, we focus on the features of the prime mover (i.e., the internal combustion engine) control strategy and on its drivers, as a function of the prescribed objective function. Results demonstrate that in the actual Italian energy market, cost minimization does not match primary energy consumption minimization, because the latter is only influenced by energy demand time series, and equipments performance, while the former is fundamentally driven by the electricity prices time series.

Enhanced Splash Models for High Pressure Diesel Spray

Mixture preparation is a crucial aspect for the correct operation of modern direct injection (DI) Diesel engines as it greatly influences and alters the combustion process and, therefore, the exhaust emissions. The complete comprehension of the spray impingement phenomenon is a quite complete task and a mixed numerical-experimental approach has to be considered. On the modeling side, several studies can be found in the scientific literature but only in the last years complete multidimensional modeling has been developed and applied to engine simulations. Among the models available in literature, in this paper the models by Bai and Gosman (Bai, C., and Gosman, A. D., 1995, SAE Technical Paper No. 950283) and by Lee et al. (Lee, S., and Ryou, H., 2000, Proceedings of the Eighth International Conference on Liquid Atomization and Spray Systems, Pasadena, CA, pp. 586-593; Lee, S., Ko, G. H., Ryas, H., and Hong, K. B., 2001, KSME Int. J., 15(7), pp. 951-961) have been selected and implemented in the KIVA-3V code. On the experimental side, the behavior of a Diesel impinging spray emerging from a common rail injection system (injection pressures of 80 and 120 MPa) has been analyzed. The impinging spray has been lightened by a pulsed laser sheet generated from the second harmonic of a Nd-yttrium-aluminum-garnet laser. The images have been acquired by a charge coupled device camera at different times from the start of injection. Digital image processing software has enabled to extract the characteristic parameters of the impinging spray with respect to different operating conditions. The comparison of numerical and experimental data shows that both models should be modified in order to allow a proper simulation of the splash phenomena in modern Diesel engines. Then the numerical data in terms of radial growth, height and shape of the splash cloud, as predicted by modified versions of the models are compared to the experimental ones. Differences among the models are highlighted and discussed. Copyright © 2007 by ASME.

A Mixed Numerical-Experimental Analysis for the Development of a Partially Stratified Compressed Natural Gas Engine

In modern DI Diesel engines with high pressure injection systems, the impingement of the spray on the piston head frequently occurs. Being the mixture preparation a crucial aspect for the correct operation of the engine, as it greatly influences and alters the combustion process, numerical modeling of the spraywall interaction becomes essential. Three different spray-wall interaction models have been tested and integrated into a modified version of the KIVA-3V. All the models conserve mass, momentum and energy of the impinging droplet and have a different behaviour if the surface is wet or dry. The paper focuses on the main features of the single models, investigating the different criteria used to define the splash occurrence, the ratio of the splashed mass to the incident mass and the splashed droplet size. Comparisons with experimental data are presented. The effects of the initial injection velocity and the spray cone angle are also investigated.

Cell Shape Influence on Mass Transfer and Backpressure Losses in an Automotive Catalytic Converter

The development of catalytic converter systems for automotive applications is, to a great extent, related to monolith catalyst support materials and design. In this paper improvements of converter channels fluiddynamics aiming to enhance pollutant conversion in all the engine operating conditions are investigated with respect to the role of channel cross-section shape on mass and heat transfer processes. The performances of different channel sections, characteristic of ceramic and metallic monoliths, have been compared by two strategies (respectively equal cell density and equal hydraulic diameter). The results have been examined in terms of mass conversion efficiency, thermal behavior and single channel backpressure for coated and non coated single channels. 3D numerical simulations have been used as an analysis tool to give a detailed insight of in-channel phenomena. Classical shapes have been analyzed and their relative performances are reported. Improvement strategies have been analyzed as well and evaluated allowing an enhancement of pollutant conversion and thermal response with non-relevant drawbacks in terms of backpressure with regard to an analogous classical empty-channel solution.

Optimization of CHCP Operation Strategy: Cost vs Primary Energy Consumption Minimization

An effective methodology to determine the optimal operational strategy for a complex CHCP plant is presented. The model is based on the minimization of a chosen variable and it is organically developed integrating thermodynamics and economics. The graph-based optimization algorithm is developed in order to find the optimal set-points of the energy system components in a sufficiently short-time. By this way the model is applicable to real industrial problems, especially when the energy is sold to the electricity market. The problem in study is discretized in time and plant states, represented as weighted graph, and the strategy that minimizes the total cost is determined using backward dynamic programming. The proposed methodology has been applied to the optimization of the set-point of an internal combustion engine based plant used to satisfy an hospital energy load, under different seasonal load conditions (winter, summer and transitional seasons) and energy prices. Two different optimization criteria are considered, namely economical optimization and primary energy consumption minimization. It is then demonstrated that the model can be effectively applied to analyze the cost and profit in energy conversion in power plants, related to electricity price, fuel price, running of turbine and auxiliary equipment, service power consumption. In particular, the chosen test case demonstrates not only the model reliability but also the economical and thermodynamic convenience of using the model itself to optimize the plant.Copyright

Optimal Management of Power Systems

The increasing energy demand along with the growing concern for environmental issues make energy saving one of the main tasks of present times and it is likely to become even more important in the next decades, as the economic growth is being pursued in developing countries, as China, India and Brazil. As a consequence, researchers, industries and politicians are required to make significant efforts in this field. More and more stringent regulations on pollution and CO2 emissions have been issued, which means limiting energy consumption. However, even if policy is an important tool, it cannot be the only one and it is necessary to spread the knowledge on energy systems, energy saving options and energy use rationalisation (Lopes et al., 2005). This is a prerequisite to make right choices for a more efficient use of energy, even if these choices are not mandatory from a “legal” point of view. Being obvious that this knowledge should be transferred to all the population layers, it is important that the main energy users, as industry, realize that energy is not merely an overhead, as part of business maintenance, but actually a raw material resource required to run the business. Energy management programs should, therefore, become an integral part of the corporate strategy, to increase the business’ profitability and competitiveness. Moreover, knocking down energy costs most of the times means reducing demand on the world’s finite energy sources, cutting pollution and creating a healthier working environment. The main example in this context is Japan, as the Japanese economy is the most energy efficient in the industrialized world and their improvements in energy efficiency enabled the Japanese industry to increase its output of 40% by spending the same energy in 2001 as in 1973 (Van Schijndel., 2002; Kamal, 1997). In general, the application of good energy management practices and energy-efficient equipment allow a readily achievable, costeffective, 20% reduction in industrial consumption (Smith et al., 2007) Energy saving can be realised through different actions on both the utilisation and the production sides (Agency for Natural Resources and Energy, 2004; Meier, 1997). However, it is really a complex task, as many factors influence energy usage, conversion and consumption and these factors are strictly connected to each other. For example, when 9

A Multidimensional Model to Simulate Direct Gaseous Fuel Injection in Internal Combustion Engines

As a consequence of the endless price growing of oil, and oil derivate fuels, automotive industry is experiencing a concerning decreasing in sales. Accordingly, in order to meet customer needs, there is every day a greater interest in solutions for increasing engine efficiency. On the other hand the growing attention to environmental problems leads to increasingly restrictive regulations, such as European EURO 4 and EURO 5. Direct injection of gaseous fuel has emerged to be a high potential strategy to tackle both environmental and fuel economy requirements. However since the electronic gaseous injection technology is rather new for automotive applications, limited experience exists on the optimum configuration of the injection system and the combustion chamber. To facilitate the development of these applications computer models are being developed to simulate gaseous injection, air entrainment and the ensuing combustion. This paper introduces a new method for modelling the injection process of gaseous fuels in multi-dimensional simulations. The proposed model allows holding down grid requirements, thus making it compatible with the three-dimensional simulation of an internal combustion engine. The model is validated and calibrated by comparing numerical results with available experimental data. To highlight the potential applications, some numerical results of the three-dimensional combustion process in a gas engine are presented.Copyright