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Pre-chamber ignition is one of the advanced technologies to improve the combustion performance for lean combustion natural gas engine, which could achieve low NOx, simultaneously. The designing scheme of the orifices, which connects the pre-chamber and the main chamber, is the main challenge limiting the further improvement. In this work, the three-dimensional computational fluid dynamics calculation based on a four-stroke engine with 320 mm cylinder bore was conducted to investigate the effects of orifice structure on the combustion and NOx performance. The results show that the schemes with 7 and 9 orifices lead to the delayed high-temperature jets formation due to the asymmetrical airflow in the pre-chamber, which retards the ignition timing but enhances the combustion in the main chamber. The 6 orifices scheme leads to the insufficient distribution of the high-temperature jets, and the 10 orifices result in the serious interference between the adjacent high-temperature jets.

For liquid fueled engine, the fuel atomization affects fuel’s evaporation, combustion, noise and vibration characteristics eventually. In this study, the effects of fuel species on the internal flow and near field primary breakup characteristics of a nozzle “Spray C” are investigated. Based on the framework of OpenFOAM, the newly developed solver which coupled cavitation model and the multifluid-quasi-VOF (Volume-of-Fluid) model, and combines the LES (Large Eddy Simulation) are applied to simulate the nozzle inner flow and near field jet breakup when using diesel and biodiesel respectively. The transient characteristics of nozzle inner flow and near field spray of two different fuels were analyzed, and the variation of axial pressure and velocity of nozzle was obtained. The simulation results show that the cavitation of biodiesel with high viscosity and low saturated vapor pressure develops slower and weaker.

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.

Increasingly strict emission regulations and unfavorable economic climate bring severe challenges to the energy conservation of marine low-speed engine. Besides traditional methods, the energy and exergy analysis could acknowledge the losses of fuel from a global perspective to further improve the engine efficiency. Therefore, the energy and exergy analysis is conducted for a marine low-speed engine based on the experimental data. Energy analysis shows the exhaust gas occupies the largest proportion of all fuel energy waste, and it rises with the increment of engine load. The heat transfer consumes the second largest proportion, while it is negatively correlated to engine load. The energy analysis indicates that the most effective way to improve the engine efficiency is to reduce the energy wasted by exhaust gas and heat transfer. However, the latter exergy analysis demonstrates that there are other effective approaches to improve the engine efficiency.

Ejector as a work recovery device offers potential for developing energy efficient heating and cooling systems based on vapor compression technology. For applications like automobile air conditioning, the operating conditions vary significantly which can lead to considerable performance degradation when the system is operated in off-design conditions. Therefore, system designing warrants development of accurate ejector performance models for a wide range of operating conditions. In this paper, a novel methodology for ejector performance maps is proposed using ejector efficiency as performance parameter and volumetric entrainment ratio as characterization parameter. The proposed performance map is developed after conducting experiments to find appropriate performance representation where ejector driven flow can be characterized using ejector motive flow. The developed performance map can predict ejector pressure lift within an accuracy of 20% using an iterative solver.

In the air conditioning system, flow-induced noise is very disturbing, including the noise generated in the expansion device and the heat exchangers. In the past few decades, most researches related to flow-induced noise focused on the relationship between the flow regimes near the expansion device and the amplitude of flow-induced noise when the measurements are not synched. In this paper, an experimental approach is used to explore the simultaneous relationships between flow-induced noise characteristics and flow regimes at the inlet of TXV of evaporators used in automobiles. A pumped R134a loop with microphones and transparent visualization sections is used to simulate the vapor compression system. Also, the paper evaluates the severity of flow-induced noise from not only the amplitude of noise but also the frequency of noise with a parameter called psychoacoustic annoyance (PA).

The modeling of fuel jet atomization is key in the characterization of Internal Combustion (IC) engines, and 3D Computational Fluid Dynamics (CFD) is a recognized tool to provide insights for design and control purposes. Multi-hole injectors with counter-bored nozzle are the standard for Gasoline Direct Injection (GDI) applications and the Spray-G injector from the Engine Combustion Network (ECN) is considered the reference for numerical studies, thanks to the availability of extensive experimental data. In this work, the behavior of the Spray-G injector is simulated in a constant volume chamber, ranging from sub-cooled (nominal G) to flashing conditions (G2), validating the models on Diffused Back Illumination and Phase Doppler Anemometry data collected in vaporizing inert conditions.

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.

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.

A new approach of NOx reduction in the compression-ignition engine is introduced in this work. The previous research has shown that during the combustion stage, the high temperature ignition tends to occur early at the near-stoichiometric region where the combustion temperature is high and majority of NOx is formed; Therefore, it is desirable to burn the leaner region first and then the near-stoichiometric region, which inhibits the temperature rise of the near-stoichiometric region and consequently suppresses the formation of NOx. Such inverted ignition sequence requires mixture with inverted phi-sensitivity. Fuel selection is performed based on the criteria of strong ignition T-sensitivity, negligible negative temperature coefficient (NTC) behavior, and large heat of vaporization (HoV).

This paper presents a simulation model for a reversible air conditioning and heat pump system for electric vehicles. The system contains a variable speed compressor, three microchannel heat exchangers, an accumulator, and two electronic expansion valves. Heat exchangers are solved by discretizing into cells. Compressor and accumulator models are developed by fitting data with physical insights. Expansion valves are modeled by isenthalpic processes. System performance is calculated by connecting all parts in the same way as the physical system and solved iteratively. The model is reasonably validated against experimental data from a separate experimental study. Future improvement is needed to take into account maldistribution in outdoor heat exchanger working as an evaporator in HP mode. Charge retention in components also requires further study.

Increasing energy costs justify research on how to improve utilization of low-grade energy that is abundantly available as waste heat from many thermodynamic processes such as internal combustion engine cycles. One option is to directly generate cooling through absorption/adsorption or vapor jet ejector cycles. As in the case of power generation cycles, cooling cycle efficiencies would increase if the heat input were available at higher temperature. This paper assesses the feasibility of a novel idea that uses a vortex tube to increase the available temperature levels of low-grade heat sources. The desired temperature increase is achieved by sending a stream of vapor that was heated by the waste heat source through a vortex tube, which further elevates the temperature used in a heat driven ejector cooling cycle.

This paper presents the experimentally obtained performance characteristics of an air conditioning-heat pump system that uses heat exchangers from a commercially available Nissan Leaf EV. It was found that refrigerant charge needed for cooling operation was larger than that for heating function with the test setup. The effects of: a). indoor air flow rate, b). outdoor air flow rate, and c). compressor speed on heating capacity and energy efficiency were explored and presented. Appropriate opening size of expansion valve that controlled subcooling for better energy efficiency was discussed and results were presented. Expansion valve opening size also strongly affected charge migration. Warm-up tests at different ambient conditions showed the necessity of a secondary heater to be reserved for very low ambient temperature.

This paper presents the experimental analysis of separation in vertical headers based on flow visualization. Two-phase separation phenomena inside the header is observed and quantified. Driving forces are analyzed to study the mechanisms for two-phase flow motion and flow regimes. Main tube of the header is made of clear PVC for visualization study. R-134a is used as the fluid of interest and the mass flux from the inlet pass is 55 kg/m2s - 195 kg/m2s. Potential ways to improve two-phase separation are discussed. A model is built to show how separation brings potential benefits to MAC heat exchangers by arranging the flow path.

The intersecting hole nozzle, in which each orifice is formed by the converging of two or more child-holes, was proposed for the purpose of enhancing the internal turbulence in diesel nozzle, so as to promote the fuel atomization. In this paper, the internal flow characteristics of a cylindrical hole nozzle and two intersecting hole nozzles are studied by CFD simulation. The results show that, compared with conventional cylindrical hole nozzle, the internal flow of intersecting hole nozzles is characterized with slower rate of pressure decrease in the hole, none or very little cavitation, as well as about 20% to 30% higher discharge coefficients, especially under conditions of high injection pressure. Additionally, the setting of the blind hole as a disturbing domain in the intersecting hole nozzle results in more perturbation for internal flow, which will be beneficial for fuel atomization.

Much attention has been given in recent years to the use of two-phase ejectors and particularly to the performance of the standard ejector cycle with a liquid-vapor separator. However, this cycle may not be the best choice for automotive applications due to the large size required by an efficient separator as well as the cycle's performance at conditions of lower ejector potential. A limited amount of recent research has focused on alternate two-phase ejector cycles that may be better suited for automotive applications. One of these cycles, using the ejector to allow for evaporation at two different temperatures and eliminating the need for a separator, will be the subject of investigation in this paper. Previous investigations of this cycle have been mainly theoretical or experimental; this paper aims to provide a numerical analysis of the effect of evaporator design on the performance of the ejector cycles.

Due to the latent heat of vaporization, the efficiency of boiling heat transfer is several times and even dozens of times higher than that of the convection heat transfer. With the improvement of power density of the engine, there are more requirements for engine cooling system design. It has been confirmed that the subcooled boiling did exist in the engine cooling. If boiling heat transfer can be reasonablely used, we can achieve the objective of enhancing heat transfer without changing the existing structure. In this paper, in order to quantitatively research the subcooled boiling in the engine, we simulated the subcooled boiling in the analog channel with the Euler multiphase model, found the importance of the turbulent dispersion. In additon, we explored the applicability of existing models to subcooled boiling, and compared the results with the experiment.

As the cost and complexity of modern aircraft systems advance, emphasis has been placed on model-based design as a means for cost effective subsystem optimization. The success of the model-based design process is contingent on accurate prediction of the system response prior to hardware fabrication, but the level of fidelity necessary to achieve this objective is often called into question. Identifying the key benefits and limitations of model fidelity along with the key parameters that drive model accuracy will help improve the model-based design process enabling low cost, optimized solutions for current and future programs. In this effort, the accuracy and capability of a vapor cycle system (VCS) model were considered from a model fidelity and parameter accuracy standpoint. A range of model fidelity was evaluated in terms of accuracy, capability, simulation speed, and development time.

The paper presents a semi-empirical model to predict refrigerant and lubricant inventory in both evaporator and condenser of an automotive air conditioning (MAC) system. In the model, heat exchanger is discretized into small volumes. Temperature, pressure and mass inventory are calculated by applying heat transfer, pressure drop and void fraction correlations to these volumes respectively. Refrigerant and lubricant are treated as a zeotropic mixture with a temperature glide. As refrigerant evaporates or condenses, thermophysical properties are evaluated accordingly with the change of lubricant concentration. Experimental data is used to validate the model. As a result, refrigerant and lubricant mass is predicted within 20% in the evaporator. However, in the condenser, lubricant mass was consistently under-predicted while refrigerant mass was predicted within 15% error. Moreover, the lubricant under-prediction becomes more significant at higher Oil Circulation Ratio (OCR).

The numerical models presented in this study are established based on discrete phase model (DPM) of spray dispersion and evaporation considering the cold wall operating condition of port injection system. All the models were implemented into the CFD software FLUENT. Gas flow and film flow and spray are coupled by mass, momentum and energy transfer due to spray impingement, film evaporation and surface shear stress. Influences of impact parameters including injection height, injection duration and injection angle on the formation and evaporation of wall-film are discussed. The results show that, with the increase of injection height, the maximum film thickness and wall film ratio decrease, and fuel vapor mass ratio increases. The reductions of film thickness and wall film ratio are not obvious as the increasing of injection height. Extending the injection duration could add the maximum film thickness and film area.