Abstract
As an effective clean fuel, ethanol has the characteristics of improving antiknock quality and reducing emissions. It is an ideal antiknock additive for Homogeneous Charge Compression Ignition (HCCI) engines. The oxidation of gasoline-ethanol surrogates in HCCI engines is a very complex process which is dominated by the reaction kinetics. This oxidation process directly determines the performance and emissions of HCCI engines. Coupling the computational fluid dynamic (CFD) model with the gasoline-ethanol surrogate mechanism can be used for fuel design, so the construction of a reduced mechanism with high accuracy is necessary. A mechanism (278 species, 1439 reactions) at medium and low temperatures and experiments in a HCCI engine for the oxidation of gasoline-ethanol surrogates were presented in this paper. Directed relation graph with error propagation (DRGEP) method and quasi-steady-state assumption (QSSA) method were used in order to get a reduced model. Then, the kinetics of the vital reactions related to the formation and consumption of H and OH were adjusted. To validate the model, the HCCI experiments for the oxidation of gasoline-ethanol surrogates were conducted under different operating conditions. The verification result indicated that the present model can predict the oxidation process of gasoline-ethanol effectively.
Highlights
Due to rapid urbanization and industrialization, pollution levels are increasing at an alarming rate recently
The application of the detailed model for complex gasoline-ethanol surrogate fuels in Homogeneous Charge Compression Ignition (HCCI) engine simulations is not practical with current computing resources, due to the large scale and the stiffness of the detailed mechanism. erefore, the representative components of gasoline should be selected reasonably and the model of multicomponent gasoline surrogates should be reduced while maintaining its good performance
More and more experiments were conducted in HCCI engines under high pressure, medium and low temperatures, and low equivalent ratio conditions, which provided a basis for the application of Primary reference fuel (PRF) mechanism in HCCI engine simulations. e PRF oxidation process of “the first oxygen addition ⟶ the first isomerization ⟶ the second oxygen addition ⟶ the second isomerization” is the key section during the autoignition process
Summary
Due to rapid urbanization and industrialization, pollution levels are increasing at an alarming rate recently. The PRF mechanism constructed [5] by using the hierarchical expansion method can be used to calculate emissions of PHAs and other pollutants, it was not accurate in predicting τ under the intake temperature (Tin) range of 300 K ∼ 434 K and the pressure (P) of 4.0 MPa. e model of Curran et al [6] can well predict the ignition process on a wider scale of Tins, Ps, and φs. Its calculated τs were highly consistent with the experimental values Based on this model, a three-component model [14] was proposed by adding some elementary reactions related to H and updating relevant kinetic parameters, which can predict SLs and τs accurately. In 2019, Li et al [16] developed a highly reduced four-component gasoline-ethanol model, which may predict the experimental data for PRF, toluene primary reference fuel (TRF), and PRF-ethanol surrogates. In order to carry out extensive validation of this reduced model, the calculation used by the proposed model should be compared with the results of the HCCI experiments, and the new model should be compared with the previous literature models
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