Numerical Simulation of High-Pressure Fuel Spray by Using a New Hybrid Breakup Model

Proceedings of the Institution of Mechanical Engineers, Part A:

et al. 2018

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An improved droplet breakup model coupled with the effect of turbulence flow within the nozzle was implemented into the general transport equation analysis code to describe the flame lift-off length and predict the soot distribution. This model was first validated by the non-evaporating and evaporating spray experimental data. The computational results demonstrate that the breakup model is capable of predicted spray penetration and liquid length with reasonable accuracy. The inclusion of turbulence enhanced the breakup model, increased the droplet breakup rate, decreased spray penetration for about 6-12% compared to the results of Kelvin-Helmholtz Rayleigh-Taylor (KH-RT) breakup model. Then, the model was applied to investigate the influence of ambient density, temperature, oxygen concentration and injection pressure on the flame lift-off length under typical diesel combustion conditions. The predictions showed good agreement with the experimental data. The result also indicated that the turbulence inside the nozzle strengthen the rate of breakup, resulting in more smaller droplets, leading to high evaporation rate and smaller vapour penetration lengths, thus decreases the lift-off length about 8%. Finally, the model was used to explore the soot distribution. The overall trend of soot with the variations in injection pressure was well reproduced by the breakup model. It was found that the droplet with faster velocity under high injection pressure, this could lead to larger lift-off length, which will play a significant role for the fuel-air mixing process and thus cause a decrease in soot in the fuel jet. Results further indicated that the turbulence term can decrease the soot mass about 5-9% by improved the droplet breakup process.

Section: Droplet Breakup Modelmentioning

confidence: 99%

Effect of hybrid breakup modelling on flame lift-off length and soot predictions

Zhang

Proceedings of the Institution of Mechanical Engineers, Part A:

et al. 2018

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“…In our previous studies, 25,26 a new hybrid breakup model was presented by considering the effect of turbulence inside the nozzle and the second breakup was modified based on the deformation of the droplet. The breakup model can be divided into primary breakup and second breakup.…”

Section: Droplet Breakup Modelmentioning

confidence: 99%

A comparison of spray and combustion characteristics of biodiesel (soy methyl ester, rapeseed methyl ester) with diesel

Proceedings of the Institution of Mechanical Engineers, Part D:

Jilani

et al. 2018

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Physical properties are known to play a pivotal role in the different characteristics of spray, combustion, and emission between diesel and biodiesel. This paper reports the development and application of physical properties of diesel and biodiesel for fuel spray and combustion modeling under various conditions. An integrated numerical model has been developed based on the General Transport Equation Analysis code. The effect of turbulence in the nozzle was considered by the hybrid breakup model in the simulation, and the skeletal mechanism of diesel surrogate fuel and biodiesel surrogate fuel was used to simulate fuel oxidation. The results indicated that liquid lengths and droplet sizes are always higher for biodiesel because of its bigger surface tension and worse vaporization characteristics caused by higher critical temperature and lower vapor pressure. This phenomenon has strong influence on fuel evaporation process and results in slow evaporation rate, and this is not helpful for the mixture preparation process. The effects of ambient density, ambient temperature, and oxygen concentration on ignition delay and lift-off length of diesel and biodiesel are also analyzed and discussed. This analysis revealed that longer ignition delay usually results in longer lift-off length and biodiesel always has longer ignition delay and lift-off length compared to diesel. The flame propagation was observed to be similar for both fuels. In addition, diesel and biodiesel were employed to simulate the combustion and emission characteristics of a low-temperature combustion engine. The different combustion and NOx emission characteristics between diesel and biodiesel were observed, and the different physical properties may be the reason for these discrepancies.

Numerical Investigation of Combustion and Emission With Different Diesel Surrogate Fuel by Hybrid Breakup Model

Journal of Engineering for Gas Turbines and Power

Peng

et al. 2018

Injection flow dynamics plays a significant role in fuel spray; this process controls the fuel–air mixing, which in turn is critical for the combustion and emissions process in diesel engine. In the current study, an integrated spray, combustion, and emission numerical model is developed for diesel engine computations based on the general transport equation analysis (GTEA) code. The model is first applied to predict the effect of turbulence inside the nozzle, which is considered by the submodel of hybrid breakup model on diesel spray process. The results indicate that turbulence term enhances the rate of breakup, resulting in more new droplets and smaller droplet sizes, leading to high evaporation rate with more evaporated mass. The model is also applied to simulate combustion and soot formation process of diesel. The effects of ambient density, ambient temperature, oxygen concentration and reaction mechanism on ignition delay, flame lift-off length, and soot formation are analyzed and discussed. The results show that although higher ambient density and temperature reduce the ignition delay and cause the flame stabilization location to move upstream, this is not helpful for fuel–air mixing because it increases the soot level in the fuel jet. While higher oxygen concentration has negative effects on soot formation. In addition, the model is employed to simulate the combustion and emission characteristics of a low-temperature combustion engine. The overall agreement between the measurements and predictions of in-cylinder pressure, heat release, and emission characteristics are satisfactory.