Numerical Simulation of Transcritical/supercritical Injection Characteristics of Diesel Engine Fuel

doi:10.12382/bgxb.2022.1012

Abstract

Abstract:

For the complex changes in spray characteristics of diesel engine under working conditions, this paper uses CFD software CONVERGE to simulate and analyze the jet spray characteristics of n-heptane fuel in transcritical/supercritical diesel engine by using large eddy simulation method, and conducts an in-depth study on turbulent subgrid model of LES. The spray characteristics of the transcritical/supercritical jet are compared from mass fraction, density and temperature. The results show that the stochastic turbulence dispersion model can make the predicted values of gas phase and liquid phase penetration distances closer to the test values, and the predicted gas and liquid phase penetration distances for turbulent dispersion coefficient c_ps=0.16 are more consistent with the test results than those for c_ps=0.05. Compared with the transcritical jet, the temperature diffusion of supercritical jet spray is faster, and the temperature of spray front is close to the ambient temperature. The similar liquid region in the transcritical jet forms a larger density stratification, which inhibits spray diffusion. Therefore, the flocculent structure in the spray outer layer of supercritical jet appears earlier than that of the transcritical jet. The flocculent structure has a larger range, and the density is closer to the surrounding environment. It is also found that the distributions of temperature, density and mass fraction in the two states show a certain corresponding relationship, that is, the temperature, mass fraction and density are all maximum at the central axis close to the injector, and decrease with the increase of axial and radial distances.

Key words: diesel engine, fuel, transcritical/supercritical jet, spray characteristics, stochastic turbulence dispersion model

CLC Number:

TK421

LIU Yuhao, XIE Fangxi, LIU Chengjun, LIU Yu, HONG Wei. Numerical Simulation of Transcritical/supercritical Injection Characteristics of Diesel Engine Fuel[J]. Acta Armamentarii, 2024, 45(5): 1416-1425.

Figures/Tables 13

Table 1 Calculation model selection

模型类别	模型名称
气态状态方程	PR方程
求解器	PISO(基于密度)
分布类型	均匀分布
湍流扩散模型	O’Rourke
碰撞模型	NTC
碰壁模型	Wall Film
破碎模型	KH-RT(KH-ACT修正)
湍流模型	LES模拟
蒸发模型	Frossling modeling模型

Fig.1 Geometric model of constant volume combustion bomb

Table 2 Initial conditions of constant volume combustion bomb

初始条件	数值
定容弹温度/K	1000
定容弹压力/MPa	4.33
燃料质量/mg	17.8
N₂体积分数/%	89.71
CO₂体积分数/%	6.52
H₂O体积分数/%	3.77

Table 3 Another names for calculation cases and corresponding parameters correction and selection

算例	燃油喷射温度/K	燃油喷射压力/MPa	燃料质量/mg
Case1	373	150	17.8
Case2	541	150	17.8

Fig.2 Comparison of penetration distance when the base mesh is 1mm/2mm/4mm

Fig.3 Spray images at different moments when turbulent dispersion coefficient cps is 0/0.05/0.16

Fig.4 Spray penetration distance curves for cps=0/0.05/0.16

Fig.5 Comparison of simulated and experimental spray penetration distances

Fig.6 Comparison of experiment (left) and simulated (right) n-heptane mass fractions

Fig.7 Temperature distribution of transcritical/supercritical jet sprays at each time

Fig.8 Enlarged views of the temperature distributions of transcritical(left)/supercritical(right) jets at 0.3ms

Fig.9 Density distribution of transcritical/supercritical jet spray at each time

Fig.10 Mass fraction distribution of transcritical/supercritical jet spray at each time

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