Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
NEGATIVE TEMPERATURE COEFFICIENT - THE INFLUENCE ON FUEL SURROGATE FORMULATION
Submission Author:
Moisés Sousa , PA
Co-Authors:
Moisés Sousa, Vinicius Rugeri Borges Bonini, Kathleen Mayara Balestrin, Jônatas Vicente, Leonel R Cancino
Presenter: Moisés Sousa
doi://10.26678/ABCM.COBEM2021.COB2021-1197
Abstract
Fuels are composed of hundreds of hydrocarbons, making their analysis complex and challenging, computationally or experimentally. An approach employed is the definition of fuels surrogates (mixtures of a reduced number of chemical species), including two or more from each class of hydrocarbons that composes conventional fuels. Normal paraffins produce cold flame/pre-ignition phenomena, characterizing the Negative Temperature Coefficient (NTC) over the pre-auto-ignition period, increasing reactivity, and reducing the ignition period at low temperatures. On the other hand, branched-chain paraffins are more resistant to ignition, which means that reactivity is not affected at low temperatures. In this work, a numerical evaluation was carried out on the influence of normal paraffins in fuel surrogates composition based on the ignition delay times (IDT). Four mixtures were evaluated, involving n-heptane, i-octane, toluene, ethanol, di-iso-butylene, methyl-cyclohexane, and 1-hexane, using a "base surrogate" with 0% vol.% of n-heptane in each and then increasing the percentage by volume on four additional compositions. IDT simulations were performed using in-house PYTHON scripts using the CANTERA toolkit for temperature range from 650 to 1200 K, pressures of 10, 30, and 50 bar at stoichiometry. The simulation results were validated with experimental data available in the literature. The results show that NTC can sometimes be indirectly attenuated by the presence of another class of hydrocarbons (toluene, for example) in the fuel surrogate formulation.
Keywords
Negative Temperature Coefficient, Fuel surrogate, Detailed kinetics model, n-paraffins
