• Energy Research

The paper introduces a numerical tool based on a predictor-corrector continuation algorithm to obtain the bifurcation analysis of a perfectly stirred reactor with detailed reaction mechanisms.Each step of the continuation algorithm is reviewed and adapted to handle reaction mechanisms with hundreds of species and thousands of reactions. Particularly, the adoption of a Broyden solver in the predictor-corrector algorithm and a new formulation of the test functions are proposed. The implementation in Matlab and the adoption of the CANTERA Toolbox, make the tool easily applicable to reaction mechanisms available in CHEMKIN format.To validate and demonstrate the capability of the tool, the full equilibrium curves have been obtained for three different cases, having increasing number of species and reactions: methane-air (GRIMech.1.2), simple surrogates of Jet-A in air (JetSurF2.0) and a ternary surrogate of Jet-A in air (CRECK). The tool gets performances that make affordable the computations even with desktop computers.

The exergy loss in laminar premixed flames of syngas is investigated numerically by analyzing the local entropy generation. The effects of the change in the H-2 molar ratio in H-2-CO mixture at different temperature values (from 300 to 600 K), at atmospheric and high pressure (10 and 50 atm) conditions and for different equivalence ratios (0.5, 1 and 2) are studied identifying both the mainly responsible process for exergy loss and the factors that can positively affect the performance of the syngas combustion. It is found that the chemical reactions are not always the main contribution to the total entropy generation (i.e. to exergy loss) and that the roles of the chemical reactions and heat conduction are strongly affected by pressure. Furthermore, it is underlined that the hydrogen content in syngas worsens the exergy loss due to entropy generation by the combustion process, whereas pressure increase has positive effects. However, these beneficial effects are counterbalanced by an increase of the chemical exergy content in the flue gases (mostly due to unreacted species or incomplete combustion). Therefore, a careful selection of the combustion process conditions is required to meet efficiency constraints if exhaust exergy is not meant to be afterward exploited. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

A system consisting of a last-generation Stirling engine (SE) and a fuel burner for distributed power generation has been developed and experimentally investigated. The heat generated by the combustion of two liquid fuels, a standard Diesel fuel and a rapeseed oil, is used as a heat source for the SE, that converts part of the thermal energy into mechanical and then electric energy. The hot head of the SE is kept in direct contact with the flame generated by the burner. The burner operating parameters, designed for Diesel fuel, were changed to make it possible to burn vegetable oils, not suitable for internal combustion engines. The possibility of adopting different configurations of the combustion chamber was taken into account to increase the system efficiency. The preliminary configurations adopted allowed to operate this integrated system, obtaining an electric power up to 4.4 kW(el)with a net efficiency of 11.6%.