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In-cylinder flow characteristics, which are mainly determined by the intake ports, have a decisive influence on the mixture formation and combustion process of internal combustion (IC) engines. To develop the optimum intake ports in a four-valve diesel engine, the full-parametric design method coupled with genetic algorithm (GA) and artificial neural network (ANN) was adopted in this study. Different from previous studies, the full-parametric templates for the tangential and helical ports were established. Then, to improve the precision of the CFD result which was used to train the ANN, the near-wall region affected by viscosity was resolved by the “enhanced wall treatment” during the simulation process. Besides, considering the interaction between the outlets of adjacent intake ports in the four-valve engine, the ANN was divided into three parts to better predict the flow performance of the combined intake ports. Finally, the developed intake ports based on ANN and GA were machined to the flow box and validated by the steady flow test. The low deviation of 4.71% in swirl ratio between the design target and the experiment result confirms that this method can be well applied to the development of the intake ports in a four-valve diesel engine.

In order to improve the in-cylinder fuel/air mixing process of heavy-duty diesel engines, optimize the combustion process and reduce the soot emissions, a new device named fuel split device (FSD) was proposed. The related numerical research of the in-cylinder velocity fields, fuel/air mixing process, combustion performance and emission characteristics of a heavy-duty diesel engine at high load was performed. The numerical results showed that the FSD had a positive effect on improving fuel/air mixing process by splitting the fuel spray, which could increase air utilization and lead to efficient combustion. Firstly, the FSD had the ability to make a better utilization of fresh air by expanding the fuel injection area; secondly, the multi-vortex structure could be formed during the fuel injection process, which could greatly improve the fuel/air mixing process. Due to the improved fuel/air mixing process with the FSD, the combustion duration was shortened by 14°CA, the indicated power delivery was increased by 6.5%, and the soot, HC, CO mass were finally reduced by 73%, 90% and 54%, respectively. It is suggested that the FSD, with its excellent combustion performance and low soot emissions, has a better application prospect in heavy-duty diesel engines.

Fischer&ndash, Tropsch (F&ndash, 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&ndash, 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&ndash, T surrogate fuel was developed, including the n-dodecane skeletal mechanism and an iso-octane macromolecular skeletal mechanism. The final mechanism for the F&ndash, 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&ndash, 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&ndash, T fuel combustion in engine accurately.

By using function vertical scaling factors, a method of construction for the fractal interpolation surfaces on a rectangular domain with arbitrary interpolation nodes is proposed. With the function vertical scaling factors, one class of iterated function systems are constructed. The existence of the unique invariant set of the iterated function system in R 3 is proved. And it is also proved that, for special vertical scaling factors, the invariant set is the graph of a continuous bivariate function passing through the given interpolation nodes.