Theoretical Investigations Into Combustion Kinetics Of Alkyled-cyclohexanes And 2-bromo-3,3,3-trifluoropropene

Cycloalkanes(usually with the alkyl side chains)are the important compounds of gasoline,diesel,and jet fuels,making up 10-30%of them.Compared with the straight chain alkanes,cycloalkanes are more prone to generate PAHs during combustion,resulting in more soot formation.Given the importance of cycloalkanes in practical applications and pollution prevention,it is imperative to fundamentally understand their combustion chemical reaction mechanisms.Moreover,Halon 1301(CF3Br)has been banned from being produced and applied because of its depleting the stratospheric ozone layer.And now,it only can be used in aviation fire extinguishing systems.Therefore,new eco-friendly replacements with the low global warming potential(GWP)and zero stratospheric ozone depletion potential(ODP)are certainly wanted.2-BTP,as one bromo-olefin,has received great attention due to its low ODP(0.0028-00052)and GWP(0.23-0.26).Therefore,the study of its combustion chemical inhibition mechanism should be conducted.First,the present work conducted the conformational study of ethylcyclohexane,cis-,and trans-1,2-cyclohexanes to reveal the impact of substituents on the conformational features of substituted cyclohexanes.The results show that the key factors for conformational behaviors of alkylated cyclohexane are the pseudorotation of six-membered ring and the different orientations of alkyl chains on the ring.Moreover,the internal rotation of alkyl chain is another important factor affecting the formation of conformational structures for substituted cyclohexane with the long side chain.For these three substituted cyclohexanes,chair conformers are more stable than twist-boat ones,which are the most abundant compounds over temperature range of 300-2500 K.The half-chair conformers serving to connect chair and twist-boat conformers have the higher energies than boat structures connecting twist-boats,leading to the inversion processes are the controlling steps for the whole conformational mechanisms.Additionally,the interconversion of chairs must go through twist-boats.Therefore,although these twist-boat conformers are scarce under that combustion conditions,they are still ignored.To further explore the impact of conformational mechanism on the combustion kinetics of substituted cyclohexanes,six ethylcyclohexyl radicals were chosen as representatives.First,all conformational structures for six ethylcyclohexyl radicals were found by high level quantum calculations,and then the potential energy surfaces for conformations and all types of H-migrations were constructed.Based on these quantum calculations,the rate constants for all reactions were computed by using transition state theory.The kinetic predictions show that the conformations are comparatively faster than H-migrations over 300-2200 K.Afterthen,the conformational inversion-topomerization mechanism was incorporated into ethylcyclohexane pyrolysis model labeled by the complete model.Whereas,the simple model constructed in present study doesn't include the conformational mechanism.By comparing the kinetic simulation results of two models,it can be seen that the conformational inversion-topomerizaiton mechanism greatly influences the distribution of six ethylcyclohexyl radicals,and consequently affects the formations of subsequent products.Moreover,cis-1,2-dimethylcyclohexyl radicals were chose as respresentatives to explore the influence of molecular structure on the radical stabilities,the energy barriers and rate constants of H-migrations and ?-scissions.The findings in this work show that the conformation is faster than H-migration and(3-scission.And the inversion-topomerization conformation attributes to establish the quasi-equilibrium condition for conformers with the same radical site.Finally,these conformations have a significant contribution to entropic for the pseudototation of ring structure in the perspectives of thermodynamics.It is found that the ring-opening reactions of cycloalkanes radicals will generate the main products C8 long-chain alkenyl radicals through ring-opening scission.This work systemically investigated the unimolecular decomposition properties of C8 long-chain alkenyl radicals,which aims to deeply understand the combustion properties and complete the combustion model of ethylcyclohexane,and the formations of small species.According to the quantum calculations and kinetic predictions,"exo" additions are always faster than "endo" additions,and "exo"addition with three-membered ring is the fastest channel.For H-migrations,1,4 and 1,5 H-migrations are the important than others over 500-2000 K.For ? scissions,P-CC scissions are always faster than ?-CH scissions.For resonantly stabilized alkenyl radicals,?-CC scissions dominate the decompositions over the studied temperature range.For nonresonantly stabilized alkenyl radicals,?-CC scissions can dominate the whole decompositions at high temperatures,while the radical additions and H-migrations play a leading role at low temperatures.The combustion inhibition and promotion mechanisms of 2-BTP is another focus of this dissertation,which is considered as a potential alternative to Halon fire extinguishing agents.According to the quantified potential energy surfaces,it can be found that the reactions for 2-BTP with OH and H radicals includes abstraction,substitution,and double bond addition.Afterthen,the rate constants for important reaction pathways varying with temperatures and pressures were calculated by RRKM/ME methodology.These kinetic predictions and branching ratio show that the addition plays a leading role in kinetics for both two systems at low temperatures,and its dominance would to extend to the higher temperatures with increasing pressure.At the corresponding high temperatures and pressures,the Br substitutions and H ion are the dominant reaction channels for 2-BTP reacting with OH,whereas the P-scission of the initial adduct forming CF3CHCH2 and Br,and Br abstraction dominate the reactions for 2-BTP reacting with H.The results also indicates that-C(Br)=CH2 moiety may cause the fuel-like property of 2-BTP.Moreover,2-BTP reacting with H radical has a larger contribution to inhibition derived.The findings in present study could provide some theoretical information for the further study of new fire suppressants.In conclusion and perspective,this dissertation gave a brief summary of all studies and proposed a future research plan,including the conformational study of 1,3-and 1,4-dimethylcyclohexane and their role in the low temperature oxidation,and the experimental study of new fire suppressants,which would be compared the simulation results by using the model with incorporating the theoretical results in this dissertation.