An Investigation On Gasoline Surrogate Component Proportions And Its Chemical Kinetic Models

In recent years, as a new kind of combustion mode, homogeneous chargecompression ignition (HCCI) has become a worldwide research focus thanks to its highthermal efficiency and low emission. Gasoline has the potential to achieve HCCIcombustion since its excellent volatility. However, the components of gasoline are toocomplicate to be used in numerical simulation of HCCI combustion and it is necessaryto select some representative components in gasoline. In the study, two gasolinesurrogates, ternary mixture (toluene, isooctane and n-heptane, named as toluenereference fuel, TRF) and quaternary mixture (toluene, isooctane, n-heptane anddiisobutylene), are investigated.The issue of how to determine the component proportions in TRF was firstlydiscussed. The ability to resist auto-ignition of gasoline is indicated by research octanenumber (RON) and motor octane number (MON).As matching the RON and MON ofreal gasoline is the target, response surface method (RSM) was used to build the thirdorder model (TOM) to predict the octane number and determine the componentproportions of TRF. The TOM shows great accuracy in determining the componentproportions of TRF with defined octane number, and in predicting the octane numbersof TRF with defined component proportions.In addition, a TRF reduced kinetic model for surrogate was built to simulate HCCIcombustion which containing71species and196reactions. The kinetic model showgood performance in comparison with various experimental data available in theliterature including ignition delay time in shock tube experiments and in-cylinderpressure and intermediate products concentration in HCCI engine experiments.Combined with TOM, the TRF reduced kinetic model shows excellent performance insimulating the gasoline combustion.Moreover, though the analysis of TOM, aconclusion may be drawn that matching the octane number is the most imperative andparamount constrain to determine the proportion of the gasoline surrogate regardless oftheir components.The accuracy of the relation between octane number and thecomponent proportions is worth paying more attention in the future research.Olefins are popular chemical class in gasoline. In China, deep catalytic crackingprocess is widely used in oil refining which make a high amount of olefins in gasoline.As a significant chemical class, a representative olefin should be added into the gasoline surrogate. Diisobutylene (DIB) was selected to represent the olefin class in this study.Based on merging the proposed TRF reduced chemical kinetic model and a detailkinetic model of DIB, a new chemical kinetic model containing four fuel chemicalspecies was put forward. The TRF/DIB gasoline surrogate kinetic model consisting923species and3954reactions was validated by comparisons of the ignition delay time inboth shock tube and HCCI engine. The results show that TRF/DIB gasoline surrogatekinetic model can be applied in high pressure and low temperature condition. Throughthe reaction rate analysis of the important reaction in gasoline surrogate, the mainreaction pathways of the fuel was obtained.It is indicatedthat DIB contains twoconjugated olefin and they have different reactionpaths. Some small carbon moleculesare generated by DIB decomposition in the initial reaction phase, which promote thechemicalactivity of the fuel. Different fuels have different reaction paths at lowtemperature reaction phase; however, they have common reactionpaths at hightemperature reaction phase.