1,721,055 research outputs found
Generalized simulation tools for coal, biomass and organic waste gasification processes
Full text linkProduction of Olefins via Oxidative Dehydrogenation of Light Paraffins at Short Contact Times
No full textCombustion of n-C3-C6Linear Alcohols: An Experimental and Kinetic Modeling Study. Part II: Speciation Measurements in a Jet-Stirred Reactor, Ignition Delay Time Measurements in a Rapid Compression Machine, Model Validation, and Kinetic Analysis
Full text linkThis work presents new experimental data for n-C3-C6 alcohol, combustion (n-propanol, n-butanol, n-pentanol, n-hexanol). Speciation measurements have been carried out in a jet-stirred reactor (p = 107 kPa, T = 550-1100 K, φ = 0.5, 1.0, 2.0) for n-butanol, n-pentanol, and n-hexanol. Ignition delay times of ethanol, n-propanol, n-butanol, and n-pentanol/air mixtures were measured in a rapid compression machine at φ = 1.0, p = 10 and 30 bar, and T = 704-935 K. The kinetic subsets for alcohol pyrolysis and oxidation from the CRECK kinetic model have been systematically updated to describe the pyrolysis and high- and low-temperature oxidation of this series of fuels as described in Part I of this work (Pelucchi, M.; Namysl, S.; Ranzi, E. et al. Combustion of n-C3-C6 linear alcohol: an experimental and kinetic modeling study. Part I: reaction classes, rate rules, model lumping and validation. Submitted to Energy and Fuels, 2020). Part II describes in detail the facilities used for this systematic experimental investigation of n-C3-C6 alcohol combustion and presents a complete validation of the kinetic model by means of comparisons with the new data and measurements previously reported in the literature for both pyrolytic and oxidative conditions. Kinetic analyses such as rate of production and sensitivity analyses are used to highlight the governing reaction pathways and reasons for existing deviations, motivating possible further improvements in our chemistry mechanism
Improvements in the simulation of liquid fuel combustion in a low-temperature fluidized bed
No full text
A Model Investigation of Fuel and Operating Regime Impact on Homogeneous Charge Compression Ignition Engine Performance
No full textThe aim of this paper is to investigate the fundamental role of chemical kinetics on the performance maps of homogeneous charge compression ignition (HCCI) engines in terms of operability limits, engine efficiency, and emissions. The work focuses on a Ricardo E6 engine, highlighting the impact of different fuels (PRF80, PRF100, and ethanol) on ringing, misfire, and partial burn limits, as well as on several performance variables and pollutant emissions. The operability maps are calculated assuming proper criteria to identify the limits of the map in terms of ringing, misfire, and partial burn. Sensitivity analysis and rate of production analysis highlight the role of H2O2 in sustaining the combustion of ethanol at high exhaust gas recirculation (EGR) and air dilution with respect to PRF100 and PRF80 mixtures. The multizone model confirms that thermal stratification and crevices are the main factors responsible for the emissions of CO and unburned species. NOx are produced mainly via a thermal mechanism. Interaction of N2O with H and O radicals also plays a role, while a prompt mechanism does not significantly affect NOx emissions. Ethanol shows greater flexibility, lower pollutant emissions, and wider operability conditions with respect to engines fed with primary reference fuels. The paper highlights the potential of this multizone model in reproducing the engine performance. Nonreacting Computational Fluid Dynamics (CFD) simulations are first used to estimate heat and mass transfer coefficients. Then, the proposed model does not require further empirical or tuning parameters. Only the thresholds defining the operability maps are derived from the experiments and are the same for all the fuels and operating conditions investigated. The extensive comparison with a large set of experimental data shows the capability of the model to describe the effect of fuel composition and EGR the operability map, highlighting how such a tool can play an important role in understanding the chemistry controlling fuel reactivity and pollutant emissions in the different conditions. These information can support not only fuel and engine operation selection, but also their optimal design. As an example, the effects of boost and engine speed on the HCCI combustion are critically investigated, in terms of the extension of the operability region, engine thermal efficiency, and exhaust emissions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Modeling homogeneous combustion in bubbling beds burning liquid fuels
Full text linkThis paper introduces a model for the description of the homogeneous combustion of various fuels in fluidized bed combustors (FBC) at temperatures lower than the classical
value for solid fuels, i.e., 850 °C. The model construction is based on a key bubbling fluidized bed feature: A fuel-rich (endogenous) bubble is generated at the fuel injection point, travels inside the bed at constant pressure, and undergoes chemical conversion in the presence of mass transfer with the emulsion phase and of coalescence with air (exogenous) bubbles formed at the distributor and, possibly, with other endogenous
bubbles. The model couples a fluid-dynamic submodel based on two-phase fluidization theory with a submodel of gas phase oxidation. To this end, the model development takes full advantage of a detailed chemical kinetic scheme, which includes both the low and high temperature mechanisms of hydrocarbon oxidation, and accounts for about 200 molecular and radical species involved in more than 5000 reactions. Simple hypotheses
are made to set up and close mass balances for the various species as well as enthalpy balances in the bed. First, the conversion and oxidation of gaseous fuels (e.g., methane)
were calculated as a test case for the model; then, n-dodecane was taken into consideration to give a simple representation of diesel fuel using a pure hydrocarbon. The model predictions qualitatively agree with some of the evidence from the experimental data reported in the literature. The fate of hydrocarbon species is extremely sensitive to temperature
change and oxygen availability in the rising bubble. A preliminary model validation was attempted with results of experiments carried out on a prepilot, bubbling combustor fired by underbed injection of a diesel fuel. Specifically, the model results confirm that heat release both in the bed and in the freeboard is a function of bed temperature. At lower emulsion phase temperatures many combustible species leave the bed unburned, while post-combustion occurs after the bed and freeboard temperature considerably increases. This is a well-recognized undesirable feature from the viewpoint of practical application and emission control
- …
