Numerical And Experimental Investigation On Gasoline Surrogate Low Temperature Combustion Mechanism

In this study, combustion mechanism of partially premixed combustion (PPC)mode was investigated by using fully coupled multi-dimensional CFD (FIRE) andreduced chemical kinetics model combined with experiments. The details about theoxidation processes of the fuel components and emission formation has been alsodiscussed.An experimental work of the gasoline fuel and several gasoline fuel surrogateshad been investigated in a wide range of EGR (exhaust gas recirculation) rate rangingfrom0%to approximately20%. The ignition delay, main combustion phasing as wellas the emission characteristics of the gasoline fuel and its surrogates have beencompared. The results indicate the combustion and emission characteristics of PRF87and PRF93are not consistent with those of gasoline, while TRF25matches thegasoline fuel only at medium loads, the fuel TRF+diisobutylene can reproduces thecharacteristics of gasoline at both low and medium loads, implying it can be a propergasoline surrogate for PPC applications.Then we developed a semi-detailed chemical kinetic model for the mixture TRF+diisobutylene, the model was developed on the basis of the skeletal mechanisms forn-heptane and iso-octane, then the detailed mechanisms for toluene and diisobutylenewere added, some cross reactions between fuel components were also considered.Especially, some quantum chemical calculations were made to some key reactions forthe low-temperature oxidation of toluene and diisobutylene, and some reactions rateparameters were updated and revised. The obtained mechanism consists of473species and1267reactions, and was validated against shock tube, laminar premixedflame and HCCI experimental results. Generally good agreements were achieved.In addition, a suite of methodologies were combined to generate a global strategyfor systematic reduction of large detailed chemical kinetic models. The integratedreduction strategy is applied to our developed semi-detailed mechanism for gasolinesurrogate fuel to eventually obtain a reduced mechanism with92species and309reactions. Validation of this model shows that the model agrees well with the parentdetailed one for both homogeneous ignition and extinction applications over wideparameter ranges. It is further demonstrated that the model well reproduces themeasured laminar flame velocities of Fuel-b as a function of equivalence ratio atdifferent initial temperatures. At last, the multi-dimensional CFD (FIRE) was fully coupled with the finallyobtained reduced chemical kinetic model to investigate the details about the oxidationmechanism of the gasoline partially premixed combustion mode, and the results showthat there appears a lag in the oxidation progress of OC7H13O2H, compared toC7H15-1、C7H15OO and C7H14OOH, which is caused by the competition betweenthe decomposition of hydroperoxyalkyl radical (QOOH·) and its oxidation process.Toluene reacts by H-abstraction to give benzyl radical, which is resonance stabilizedand unreactive, thus making the oxidation of the whole mixture system inhibited.Diiisobutylene reacts by H-abstraction to give JC8H15-a, which quickly decomposesto iC4H7and iC4H8. Moreover, about20%diisobutylene is consumed through the“Waddington” mechanism, implying the oxidation process of fuel components in PPCmode is indeed different from their homogeneous low-temperature oxidation regime.