Combustion Mechanisms and Kinetics of Fuel Additives: A ReaxFF Molecular Simulation

Abstract

Fuel additives are widely used as octane number improvers, oxygenates, emission depressors, and corrosion inhibitors to promote combustion processes of liquid fuel. In this work, six kinds of fuel additives, including ethanol, butanol, dimethyl carbonate, dibutyl carbonate, methyl tert-butyl ether, and tri-tert amyl glycerol ether, were studied by ReaxFF molecular dynamics simulations. The bond dissociation reactions were found to be more dominant at the early stage than oxidation reactions, which means the unimolecular reactions were the main pathways of primary reactions in hydrocarbon combustion. The rate constants of primary reactions of ethanol combustion were much smaller than those of other systems, which were in good agreement with the product distribution analysis and previous work. The main reaction pathway and relative rate constants for all systems were evaluated. Four kinds of main radicals, including ·CH3, ··CH2, ·OH, and ·HO2, were detected, and the number variation with time are presented. The number of ·OH radicals was the largest among those four radicals, and it was found to gradually increase with time except for ether systems; the number of ·CH3 and ··CH2 radicals sharply increased first and then gradually decreased. Hopefully, the results obtained in this work will be helpful to future design and screening of new fuel additives.

Investigation on the Possibility of Increasing the Environmental Safety and Fuel Efficiency of Vehicles by Means of Gasoline Nano-Additive

“…The problem of the ecological danger of fuels and their combustion products requires one to look for integrated solutions, including new approaches in car and engine constructions [10]; improving the technological parameters of transport, with emphasis on multi-material construction for weight reduction [11]; increasing the adaptability of vehicles to operating conditions [12], in particular under weather changes [13], with application of such instruments as the dynamic vehicle scheduling [14]; tightening international and national requirements for fuel quality [15][16][17], use of tax instruments [3,[18][19][20][21]. Limited possibilities for improving the quality of motor fuels by refining methods [22][23][24] necessitate the use of fuel additives of various purposes, the combination of which in small amounts ensures the environmental and operational characteristics achieve the desired level [25][26][27][28][29][30]. Often the use of additives is the only way to ensure an optimum engine mode that allows one the commodity fuel to be quickly and flexibly adapted to the operating conditions without increasing the fuel assortment.A significant part of the additives used are surfactants.…”

Molecular dynamics simulation of soot formation during diesel combustion with oxygenated fuel addition

“…In ReaxFF simulations, employing high temperature and pressure to facilitate the collision and accelerate the simulation process is a common strategy. 19,20,24,25 A time step of 0.25 fs is adopted for both the equilibrating and reactive simulations. The species information is recorded every 100 fs while dynamic trajectory and bonding information is dumped every 250 fs.…”

“…19,20 It is a common practice to normalize the absolute rate constants using the slowest reaction obtained from ReaxFF simulations, that is, the rate constant of the slowest reaction is set to be 1. 24 The thermal pyrolysis pathways of the oxygenates and the relative kinetic rates are summarized in Table 2.…”

Combustion of Fuel JP8-1: Mechanism and Reaction Kinetics Based on ReaxFF MD

“…In addition, in the absence of inhibitors, aviation kerosene that exhibits poor thermal stability is prone to coking at high temperatures. − Previous studies described mainly, with a macro point of view, the factors influencing coking and its precursors. , Unfortunately, such studies conducted on JP8-1 did not explain the mechanism of the formation of coking.…”

“…Using the ReaxFF, the MD simulation of pyrolysis and oxidation of complex multicomponent fuel models is feasible. Chen reported the applications of ReaxFF MD in the calculation of the cracking of n -hexadecane at high temperatures and pressures, analysis of catalytic cracking of heavy hydrocarbons, study of the combustion mechanism of multicomponent heavy hydrocarbons, and development of the additive-assisted combustion mechanism of heavy hydrocarbons . Wang reported the application of ReaxFF MD to simulate the cracking of single-component n -dodecane.…”