Optical Study on Spray and Two-Stage Ignition Characteristics for Diesel Spray Under Low Ambient Temperature and Density Conditions

Li Yikai,Xue Zefeng,Shi Zhongjie,Chen Haiyan,Beijing Institute of Technology 한국자동차공학회 2023 International journal of automotive technology Vol.24 No.5

Poor atomization and ignition difficulty due to the deterioration of environmental conditions restrict the coldstart performance of diesel engine. To investigate how the ambient and injection parameters affect diesel ignition characteristics at low temperature and density, liquid spray development was measured by back-illumination method; vapor spray and ignition process were visualized using high-speed shadowgraph method in constant volume combustion chamber. The results showed that liquid-vapor penetration and two-stage ignition delay have different sensitivities to variables: the variation of ambient density greatly affects the spray development while ambient temperature is the most significant parameter affecting ignition delay. Additionally, the change of injection pressure cannot cause significant change of both liquid penetration length and low temperature ignition, but increasing injection pressure promoted the vapor penetration length downstream development. Based on the data obtained, the empirical formulation in the form of power function was fitted for the stable stage of liquid penetration length, which proposed a reference for comparing the liquid phase development characteristics of diesel spray. Similarly, revise the Arrhenius-type ignition delay prediction formula and the correction coefficient K ( and ) was optimized quantitatively instead of fixed values, provides a preliminary theoretical basis for subsequent diesel spray model.

Numerical investigation on the influence of surface tension and viscous force on the bubble dynamics with a CLSVOF method

Zhiying Wang,Yikai Li,Biao Huang,Deming Gao 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.6

We numerically investigated the rising of bubbles in a quiescent liquid layer. The numerical simulation is performed by solving the incompressible, multiphase Navier-Stokes equations via computational code in axisymmetric coordinates using a Coupled level-set and volume-of-fluid (CLSVOF) method. The numerical results show that the CLSVOF method with a novel algebraic relation between F and f for axisymmetric two-phase flows not only can predict the bubble surface accurately, but also overcome the deficiency in preserving volume conservation. The effects of the Reynolds number Re and the Bond number Bo on the bubble deformation and its motion are investigated. The results show that with the increasing of Re (10 < Re < 150), the bubble shape transfers from oblate ellipsoidal cap to toroidal when Bo = 116. With the increasing of Bo (10 < Bo < 700), the bubble shape transfers from oblate ellipsoidal to toroidal when Re = 30. Although the toroidal bubble shapes are reached in these two cases, the transition modes are different. For the case Bo = 116, the bubble front is pierced by an upward jet from the rear of the bubble. While for the case Re = 30, the rear of the bubble is pierced by a downward jet from the front part.

Cycle-Consistent Generative Adversarial Network: Effect on Radiation Dose Reduction and Image Quality Improvement in Ultralow-Dose CT for Evaluation of Pulmonary Tuberculosis

Yan Chenggong,Lin Jie,Li Haixia,Xu Jun,Zhang Tianjing,Chen Hao,Woodruff Henry C.,Wu Guangyao,Zhang Siqi,Xu Yikai,Lambin Philippe 대한영상의학회 2021 Korean Journal of Radiology Vol.22 No.6

Objective: To investigate the image quality of ultralow-dose CT (ULDCT) of the chest reconstructed using a cycle-consistent generative adversarial network (CycleGAN)-based deep learning method in the evaluation of pulmonary tuberculosis. Materials and Methods: Between June 2019 and November 2019, 103 patients (mean age, 40.8 ± 13.6 years; 61 men and 42 women) with pulmonary tuberculosis were prospectively enrolled to undergo standard-dose CT (120 kVp with automated exposure control), followed immediately by ULDCT (80 kVp and 10 mAs). The images of the two successive scans were used to train the CycleGAN framework for image-to-image translation. The denoising efficacy of the CycleGAN algorithm was compared with that of hybrid and model-based iterative reconstruction. Repeated-measures analysis of variance and Wilcoxon signedrank test were performed to compare the objective measurements and the subjective image quality scores, respectively. Results: With the optimized CycleGAN denoising model, using the ULDCT images as input, the peak signal-to-noise ratio and structural similarity index improved by 2.0 dB and 0.21, respectively. The CycleGAN-generated denoised ULDCT images typically provided satisfactory image quality for optimal visibility of anatomic structures and pathological findings, with a lower level of image noise (mean ± standard deviation [SD], 19.5 ± 3.0 Hounsfield unit [HU]) than that of the hybrid (66.3 ± 10.5 HU, p < 0.001) and a similar noise level to model-based iterative reconstruction (19.6 ± 2.6 HU, p > 0.908). The CycleGAN-generated images showed the highest contrast-to-noise ratios for the pulmonary lesions, followed by the model-based and hybrid iterative reconstruction. The mean effective radiation dose of ULDCT was 0.12 mSv with a mean 93.9% reduction compared to standard-dose CT. Conclusion: The optimized CycleGAN technique may allow the synthesis of diagnostically acceptable images from ULDCT of the chest for the evaluation of pulmonary tuberculosis.

Performance Analysis and Optimization Design of Exhaust System for Turbocharging Diesel Engines

Liu Fushui,Sun Chenghan,Li Yikai,Shang Yong 한국자동차공학회 2021 International journal of automotive technology Vol.22 No.3

Modern diesel engines are struggling to enhance the power density. This is usually realized by being equipped with a turbocharger, which demands higher performances on exhaust flow and exhaust waste energy recovery (WER). In the present study, we investigated the variations of exhaust flow and exhaust energy recovery performance with different geometrical parameters of exhaust system and proposed an evaluation and optimal design method of the exhaust system for a turbocharging diesel engine with a module pulse converter (MPC) system. The macro engine performances and the micro flow fields in exhaust system are obtained from the one/three dimensional (1D-3D) coupling simulation, and the energy of exhaust gas is quantified and analyzed with a concept of air power. It can be concluded that with a view to the exhaust performance and exhaust energy utilization, the diameter of the exhaust pipe should be set equal to the outlet diameter of the manifold and there is an optimized value of the contraction rate of the exhaust manifold. Besides, a parameter of the exhaust system called power potential coefficient is proposed to qualitatively evaluate the exhaust performance and exhaust energy.

ONLINE MEASURING METHOD FOR THE ENGINES’ IVC TIMING BASED ON THE IN-CYLINDER PRESSURE FLUCTUATION

Fushui Liu,Zhongjie Shi,Yikai Li,Yang Hua,Yanlin Chen,Yongli Gao 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.2

The in-cylinder pressure fluctuations caused by intake valve closure (IVC) event were first investigated experimentally based on a single cylinder diesel engine with different cams. The experimental results show that the occurrence of the in-cylinder pressure fluctuation during the compression stroke has a close correlation with the IVC event. The start time of the pressure oscillation advances as the IVC timing advances. With a fixed IVC timing, higher engine speed results in a larger fluctuation amplitude and a longer fluctuation duration. To explain these phenomena, a numerical simulation model has been adopted. Results show that the IVC event causes pressure oscillations in both the cylinder and intake runner. At the same engine speed, the amplitude of the pressure oscillation decreases first and then increases as the IVC retards due to the change of gas flow direction. With the same intake temperature, the absolute time delay keeps constant at different engine speeds and IVC timings. The absolute time delay decreases as the intake temperature decreases. Based on the conclusions above, the potential methods to use the pressure oscillation are also discussed. An innovative engine valve timing detection method on the basis of in-cylinder pressure oscillation is presented.

Research on Cold-Formed Steel Stiffened-Web Built-up I-Section Columns with Complex Edge Stiffeners

Zhuangnan Zhang,Yudong Li,Chungang Wang,Yikai Hao,Jianqiao Song,Qinglin Guo 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.1

A series of double-limbs built-up I-section simply supported specimens subjected to compression were examined. The test columns contained 18 concentric compression columns and 12 eccentric compression columns with three section forms respectively. The infl uence of web stiff eners on buckling mode, ultimate bearing capacity and interaction between limbs were studied. It was shown that stiff eners in web eff ectively decreased the element width-to-thickness ratio and increased the bearing capacity of built-up I-section columns. But when larger eccentricity made the moment control the failure of eccentric compression specimens, the bearing capacity of the specimens was not improved obviously by web stiff eners. Distortional buckling could replace local buckling to control the failure modes of columns. Compared with double-limbs channel steel built-up open-sections with complex edge stiff eners under the same steel quantity and eccentricity, the load carrying capacity of double limb Σ-shaped channel built-up sections increased from 4.4% to 20.3%. While for double limb channel with V-type web stiff ener sections, the increment was from 2.2% to 17.4%. Furthermore, parametric study of 90 Σ-shaped built-up section members was investigated to obtain the optimization proportion of the web sub-element and relationship of carrying capacity between single Σ-shaped section and double limb Σ-shaped I-section. Finally, the ultimate load-carrying capacity of built-up columns subjected to axial compression were calculated by two kinds of direct strength method formulas, which were compared with the tests values. The results showed that the method considered the interaction between distortional buckling and fl exural buckling could obtain conservative results.

Experimental and numerical study on the effects of the solenoid valve motion on the fuel pressure fluctuations for electronic unit pump systems of diesel engines

Fushui Liu,Ning Kang,Pei Wang,Yikai Li 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.11

For electronic unit pump systems, it is an advantage for online combustion analysis and fault diagnosis to ascertain the relationship between the fuel pressure fluctuation and the movement of the solenoid valve. We experimentally and numerically investigated the fuel pressure characteristics and their connection to the transient motion of the solenoid valve. Four fuel pressure characteristic points corresponding to the start of closing time, the fully closed time, the start of opening time and the fully opened time of the solenoid valve were determined on the fuel pressure curve. A novel method was proposed to predict the solenoid valve displacement curve based on the four fuel pressure characteristic points. The validation results show that the displacement curves of the prediction and experiment are almost coincident, and the relative error of the injection quantity per cycle between the simulation and experiment is within 3 %.

Double-layer Fabry-P$\acute{e}$rot filter interferometric modulator display

Chen, Chao Ping,Xiong, Yuan,Yang, Yuxing,Li, Xiao,Li, Hongjing,He, Gufeng,Lu, Jiangang,Su, Yikai 한국정보디스플레이학회 2013 Journal of information display Vol.14 No.4

Presented is an interferometric modulator display characterized by double layers of liquid crystal (LC) Fabry-P$\acute{e}$rot filters. With this design, no polarizers and color filters are needed, and both the color and amplitude can be tuned by electrically controlling the LC's birefringence. Instead of the conventional RGB trisubpixel color scheme, a bisubpixel structure is proposed to render a super-wide color gamut. Through simulations, the device performance was numerically studied. The device was proven to be quite suitable for green-display application.

Double-layer Fabry–Pérot filter interferometric modulator display

Chao Ping Chen,Yuan Xiong,Yuxing Yang,Xiao Li,Hongjing Li,Gufeng He,Jiangang Lu,Yikai Su 한국정보디스플레이학회 2013 Journal of information display Vol.14 No.4

Presented is an interferometric modulator display characterized by double layers of liquid crystal (LC) Fabry–Pérot filters. With this design, no polarizers and color filters are needed, and both the color and amplitude can be tuned by electrically controlling the LC’s birefringence. Instead of the conventional RGB trisubpixel color scheme, a bisubpixel structure is proposed to render a super-wide color gamut. Through simulations, the device performance was numerically studied. The device was proven to be quite suitable for green-display application.

Power control of CiADS core with the intensity of the proton beam

Kai Yin,Wenjing Ma,Wenjuan Cui,Zhiyong He,Xinxin Li,Shiwu Dang,Feng Yang,Yuhui Guo,Limin Duan,Meng Li,Yikai Hou 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.4

This paper reports the control method for the core power of the China initiative Accelerator DrivenSystem (CiADS) facility. In the CiADS facility, an intense external neutron source provided by a protonaccelerator coupled to a spallation target is used to drive a sub-critical reactor. Without any control rodinside the sub-critical reactor, the core power is controlled by adjusting the proton beam intensity. Inorder to continuously change the beam intensity, an adjustable aperture is considered to be used at theLow Energy Beam Transport (LEBT) line of the accelerator. The aperture size is adjusted based on theProportional Integral Derivative (PID) controllers, by comparing either the setting beam intensity or thesetting core power with the measured value. To evaluate the proposed control method, a CiADS coremodel is built based on the point reactor kinetics model with six delayed neutron groups. The simulations based on the CiADS core model have indicated that the core power can be controlled stably byadjusting the aperture size. The response time in the adjustment of the core power depends mainly onthe adjustment time of the beam intensity