Abstract
Fischer–Tropsch (F–T) fuel, synthesized from coal-to-liquid (CTL), is an alternative fuel with clean and efficient characteristics. In this study, a surrogate fuel model was developed, including n-dodecane (n-C12H26) and iso-octane (i-C8H18), which represents the n-alkane and iso-alkane in F–T fuel synthesized from CTL, respectively. The proportions of the components in the surrogate fuel are determined by the characteristics of the practical fuel, including cetane number (CN), C/H ration and component composition. For the establishment of the skeletal mechanism model, firstly, based on a two-step direct relationship graph (DRG) and the computational singular perturbation (CSP) importance index method, a reduced model of n-dodecane was developed involving 159 species and 399 reactions, while the detailed n-dodecane mechanism consists of 1279 species and 5056 reactions. Then, the n-dodecane skeletal mechanism was constructed based on a decoupling methodology, involving the skeletal C12 mechanism from the reduced mechanism, a C2-C3 sub mechanism and a detailed H2/CO/C1 sub mechanism. Finally, the skeletal mechanism for the F–T surrogate fuel was developed, including the n-dodecane skeletal mechanism and an iso-octane macromolecular skeletal mechanism. The final mechanism for the F–T diesel surrogate fuel consists of 169 species and 406 reactions. The n-dodecane skeletal mechanism and iso-octane skeletal mechanism were validated on various fundamental experiments, including the ignition delay in shock tubes, the primary species concentrations in jet-stirred reactors and the premixed laminar flame over wide operating conditions, which show great agreement between the predictions and measurements. Moreover, an F–T surrogate fuel mechanism was employed to simulate the combustion characteristics of an engine using computational fluid dynamics (CFD). The results show that the mechanism can predict the performance of F–T fuel combustion in engine accurately.
Highlights
High efficiency and cleaning combustion are always the goals when developing internal combustion engines (ICEs) [1]
The fundamental experimental data obtained in shock tubesand jet stirred reactors and laminar flamesare essential for assessing and validating the performance of surrogate fuel
The computational fluid dynamics (CFD) software is used to simulate the working process of a diesel engine fueled with F–T fuel, the calculation results shown in Figure 14 are in good agreement with the measurements, indicating that the skeletal mechanism can predict the performance of F–T fuel in cylinder combustion
Summary
High efficiency and cleaning combustion are always the goals when developing internal combustion engines (ICEs) [1]. Understanding the in-cylinder combustion process is important for clean and efficient utilization for F–T diesel in ICEs. At present, there are few studies on the chemical kinetic model of F–T fuel, especially for CTL. The chemical kinetic model of alkane, which is used in the construction of surrogate fuels for traditional gasoline, diesel, jet fuel or other alternative fuels, has been extensively studied. Stephen et al [4] constructed a synthetic paraffin jet fuel chemical kinetic model containing n-decane (n-C10 H22 ) and iso-octane (iso-C8 H18 ). May-Carle et al [7] studied the oxidation characteristics of F–T, F–T/biodiesel blends in jet reactors, and constructed a detailed mechanism including n-decane, iso-octane, methyl octoate and ethanol. For the CFD simulations of F–T fuel in ICEs, a reliable chemical kinetic skeletal mechanism is needed. The mechanism is validated based on various fundamental experiments and a practical engine
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