Design,Construction And Application Of Flow Reactor For The Study Of Combustion Reaction Kinetics

Fundamental combustion chemistry experiments are essential to fully understand and characterize the kinetics of chemical reactions in various fossil fuels for improved combustion and emission reduction,and reliable experimental systems are needed to better assess the kinetic mechanisms of chemical reactions.In basic combustion chemistry experiments,the evolution histories of intermediates during fuel pyrolysis and oxidation are the key data for modelling chemical reaction kinetics.The flow reactor based on the plug flow principle allows precise control of conditions such as temperature,pressure and reaction time,and can cover all temperature conditions in real engine operating conditions.The common fuels used in internal combustion engines include not only gaseous compounds such as natural gas and petroleum cracking gas,but also large hydrocarbons that are liquid at room temperature and have higher boiling points,such as gasoline,kerosene,and diesel.The effective vaporization of the latter often becomes an experimental difficulty.In this paper,flow reactor system was designed and developed for small-molecule and large hydrocarbons.As representative fuels,propane,n-heptane,iso-octane and n-dodecane were investigated in pyrolysis experiment and simulations.The flow reactor system in this study contained an inlet system,a reaction system,a sampling system,an exhaust system and an analysis system.In the inlet system a microinjector pump injected fuel at a steady rate through a quartz atomizer into the vapor mixing chamber,where the fuel was rapidly mixed with dilute gas and vaporized.The heating element of the vapor mixing chamber heated the gas in the chamber to over300°C,which met the temperature requirements for vaporization of common hydrocarbons.The flow reactor of the reaction system was heated to a maximum temperature of 1700°C and experiments were carried out at low and medium temperatures using quartz and corundum tubes respectively.The T-shaped design of the exhaust system ensures that large quantities of exhaust gas can be exhausted quickly and without restricting the movement of the sampling rods along the reactor axis.The sampling system was designed with a water-cooled sampling rod,which was quenched as soon as the sample enters the rod to ensure that no chemical reaction would continue.At the same time,a mobile platform control system was developed to realize the quantitative displacement of the sampling rod,and the sampling rod could sample at different positions along the axis of the reactor.The analysis system mainly used Micro GC for separation and detection of reaction products,which can detect hydrocarbons in the range of C₀-C₁₂;NDIR and PO₂ were also used to monitor air leakage in the system in real time,and quantitatively characterize the concentrations of carbon monoxide CO,carbon dioxide CO₂ and oxygen O₂ respectively.Once the flow reactor system was set up,it was used to study the basic combustion reaction kinetics of conventional gaseous small molecules and high-boiling large hydrocarbon fuels.First,the four fuels propane,n-heptane,isooctane and n-dodecane were vapor mixed and delivered directly to the Micro GC for calibration,which also verified that the vapor mixing chamber was in good operating condition.Afterwards,the temperature profiles corresponding to the propane,n-heptane,isooctane and n-dodecane pyrolysis experiments were measured to confirm the initial conditions for the experiments and then the fuel pyrolysis experiments were carried out to obtain the mole fractions of the products including H₂,CH₄,C₂H₄,C₂H₆,C₃H₆,1-C₄H₈ and i-C₄H₈.Finally,simulations were carried out using Ansys Chemkin-Pro software for the same initial conditions,and the detailed mechanisms of Aramco 2.0 and LLNL,as well as the simplified model of TSRS,were chosen to compare the simulation results with the experimental results and to verify the reasonableness and reliability of the data for the flow reactor system.