N. Bernal

Bio: N. Bernal is an academic researcher from University of Zaragoza. The author has contributed to research in topics: Biogas & Alternative energy. The author has an hindex of 5, co-authored 5 publications receiving 109 citations.

Thermal Model of a Dish Stirling Cavity-Receiver

Abstract: This paper presents a thermal model for a dish Stirling cavity based on the finite differences method. This model is a theoretical tool to optimize the cavity in terms of thermal efficiency. One of the main outcomes of this work is the evaluation of radiative exchange using the radiosity method; for that purpose, the view factors of all surfaces involved have been accurately calculated. Moreover, this model enables the variation of the cavity and receiver dimensions and the materials to determine the optimal cavity design. The tool has been used to study the cavity optimization regarding geometry parameters and material properties. Receiver absorptivity has been identified as the most influential property of the materials. The optimal aperture height depends on the minimum focal space.

Hybridization of solar dish-stirling technology: Analysis and design

Abstract: Integration of renewable energies differentiates high concentration solar thermal technologies from photovoltaics. The popularization of high concentration solar thermal technologies facilities can be increased if alternative energy sources are used, with a significant advantage in investment recovery. As the operation hours are increased, the environmental impact is also improved. This article analyzes the hybridization of two dish-Stirling facilities, distinguishable by the two different fuels utilized: natural gas and biogas. Different considerations for the design of required elements for hybridization are presented, specifically the burner and the heat exchanger for biogas use. An evaluation of the environmental impact associated with hybridization using natural gas and then biogas is also carried out. Life Cycle Assessment (LCA) is performed with SimaPro software for each fuel scenario using: (i) the Ecoindicator-99 impact evaluation method; and (ii) CO2-equivalent emissions. Novel aspects of this study include the analysis of the global output of the hybrid system, considering two different fuels. Analysis also takes into consideration environmental criteria to establish a comparison. Results show an advantage for hybridization using biogas, a renewable source, instead of natural gas. The environmental viewpoint, considered by the LCA, adds a differential decision criterion at the same time that it favors investments in this technology. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 1459–1466, 2014

Application of hydrogen enriched natural gas in spark ignition IC engines: from fundamental fuel properties to engine performances and emissions

Abstract: This review offers a summary of the recent research progress on hydrogen enriched compressed natural gas (HCNG) engines. Spark ignition IC engines fueled by HCNG have been shown to be advantageous over traditional gasoline engines in terms of fuel efficiencies and pollutant emissions. Further taking into account the vast availability of natural gas and the renewability of hydrogen, HCNG is considered to be a promising alternative fuel for large-scale applications in spark ignition engines. The past decade has witnessed significant progress in the research and development of HCNG engines. In this work, we intend to provide a comprehensive survey of recent studies on the power, efficiency and combustion & emission characteristics of HCNG engines. Additionally, we also focus on correlating fuel properties with experimentally observed HCNG engine performances, providing fundamental insights in the effects of hydrogen addition on engine working processes. To reach this goal, the physicochemical properties of hydrogen and its mixture with natural gas were firstly analyzed, followed by the detailed presentation and analysis of notable experimental results on HCNG engine performances. Numerical models for HCNG engines, which serve as an efficient way for engine parameter optimization, were also discussed. Apart from HCNG, the usage of other hydrogen-enriched fuels, such as hydrogen-gasoline, hydrogen-diesel, biogas and hydrogen-ethanol/methanol in IC engines were also briefly discussed.