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The non-conventional diesel nozzles have attracted more and more attention for their ability to promote jet breakup. In the present study, the internal nozzle flow and jet breakup relying on the convergent-divergent nozzle are investigated by combining the cavitation model and LES model with Multi-Fluid-Quasi-VOF model based on the OpenFOAM code. This is a novel method for which the interphase forces caused by the relative velocity of gas and liquid can be taken into account while sharpening the gas-liquid interface, which is able to accurately present the evolution processes of cavitation and jet breakup. Primarily, the numerical model was verified by the mass flow rate, spray momentum flux, discharge coefficient and effective jet velocity of the prototype Spray D nozzle from the literature.

Flash boiling spray is effective in improving the atomization and evaporation characteristics for gasoline direct injection engines. However, for a multi-hole injector the morphology structure of spray has an obvious change with the fuel temperature increasing or the ambient pressure decreasing, which influences the process of mixture formation and flame propagation. Specially, the spray collapses with both long penetration and a narrow spray angle above certain high superheat degree, which deteriorates air/fuel mixing and hence increases emissions. It is not desired for engine applications while the mechanism of spray structure transformation for multi-hole injector still remains unclear. In the present study, a systematic flash boiling spray model for multi-hole injector is built to investigate the flash boiling spray of multi-hole injector.

The multi-zone model has been attracting growing attention as an efficient and accurate numerical model for homogeneous charge compression ignition (HCCI) combustion simulations. In this paper, a comparative study was carried out to clarify the effect of various sub-models on the prediction capability of the multi-zone model. The influences of the distribution of zones, heat transfer from the wall, mass and heat exchange between zones and boundary layer thickness on HCCI combustion and emissions were discussed based on the experimental data. The results indicate dividing the colder region into more zones can improve the emissions prediction, however, more zones in the hotter region has little effect on the predictions. The improved Woschni model significantly improves the prediction of heat transfer.

Multiple-injection strategy for Premixed Charge Compression Ignition (PCCI) combustion was investigated in a four-valve, direct-injection diesel engine by CFD simulation using KIVA-3V code [ 1 ] coupled with detailed chemistry. The effects of fuel splitting proportion, injection timing, included spray angles, injecting velocity, and the combined effects of injection parameters and EGR rate and boost pressure were examined. The mixing process and formations of soot emission and NO x were investigated as the main concern of the research. The results show that the fuel splitting proportion and the injection timing significantly impacted the combustion and emissions due to the considerable changes of the mixing process and fuel distribution in cylinder. The soot emission and unburned HC (UHC) were affected by included spray angles since the massive influences of the fuel distribution resulted from the change in spray targeting point on piston bowl.

Dimethyl ether (DME) attracts increasing attentions in recent years, because it can reduce the carbon monoxide (CO), unburned hydrocarbon (HC), and soot emissions for engines as the transportation fuel or the fuel additive. In this paper, a reduced DME oxidation mechanism is developed using the decoupling methodology. The rate constants of the fuel-related reactions are optimized using the non-dominated sorting genetic algorithm II (NSGA-II) to reproduce the ignition delay times in shock tubes and major species concentrations in jet-stirred reactors (JSR) over low-to-high temperatures. In NSGA-II, the range of the rate constants was considered to ensure the reliability of the optimized mechanism. Moreover, an improved objective function was proposed to maintain the faithfulness of the optimized mechanism to the original reaction mechanism, and a new method was presented to determine the optimal solution from the Pareto front.

The phenomenon of a thin liquid film separation and atomization at expanding corners during the spray/wall interaction is usually encountered in premixed charge compression ignition (PCCI) engines. However, detailed information about the film separation is very limited, especially under high injection pressure conditions. In this study, experimental study was conducted to investigate the effects of injection pressure and impingement distance on the evolutions of the impinging spray and the adhered film at simplified geometries with an expanding corner by employing a high-speed camera. In addition, an improved hybrid film separation and atomization model was developed, which includes the sub-models of film separation criterion, film separation mass ratio, and the film atomization model based on the Rayleigh-Taylor instability theory.

Multi-dimensional models coupled with a reduced chemical mechanism were used to investigate the effect of fuel on exergy destruction fraction and sources in a reactivity controlled compression ignition (RCCI) engine. The exergy destruction due to chemical reaction (Deschem) makes the largest contribution to the total exergy destruction. Different from the obvious low temperature heat release (LTHR) behavior in gasoline/diesel RCCI, methanol has a negative effect on the LTHR of diesel, so the exergy destruction accumulation from LTHR to high temperature heat release (HTHR) can be avoided in methanol/diesel RCCI, contributing to the reduction of Deschem. Moreover, the combustion temperature in methanol/diesel RCCI is higher compared to gasoline/diesel RCCI, which is also beneficial to the lower exergy destruction fraction. Therefore, the exergy destruction of methanol/diesel RCCI is lower than that of gasoline/diesel RCCI at the same combustion phasing.

Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at low, mid, and high loads. By coupling the KIVA-3V code with the enhanced genetic algorithm (GA), a total of 14 parameters including the piston bowl geometric parameters and the injection parameters were optimized with the objective of meeting Euro VI regulations while improving the fuel efficiency. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized and integrated at various loads. Furthermore, the effects of the key geometric parameters were investigated in terms of organizing the in-cylinder flow, influencing the energy distribution, and affecting the emissions. The results indicate that the behavior of the DMDF combustion mode is further enhanced in the aspects of improving the fuel economy and controlling the emissions after the bowl geometry optimization.

The flow performance of intake port significantly affects engine output power, fuel economy, and exhaust emissions in gasoline engines. Thus, optimal intake port geometry is desired in gasoline engines. To optimize the flow performance of intake port, a new optimization method combining genetic algorithm (GA) and artificial neural network (ANN) was proposed. First, an automatic system for generating the geometry of the tangential intake port was constructed to create various port geometries through inputting the 18 pre-defined structural parameters. Then, the effects of four critical structural parameters were investigated through numerical simulation. On the basis of the computational results, an ANN was used to model the flow performance of the intake port, and a genetic algorithm was simultaneously employed to optimize the flow performance by optimizing the four important structural parameters. Finally, the optimization results were verified through numerical simulation.

The potential of diesel/gasoline RCCI combustion coupled with late intake valve closing (LIVC) and double direct injection of diesel for meeting high fuel efficiency with ultra-low emissions was investigated in this study. The study was aiming at high load operation in a heavy-duty diesel engine. Based on the reactivity stratification of RCCI combustion, the employment of double injection of diesel fuel provided concentration stratification of the high-reactivity fuel, which is to further realize effective control of the combustion process. Meanwhile, late intake valve closing (LIVC) strategy is introduced to control the maximum in-cylinder pressure and nitrogen oxides (NOx) emissions.