• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.20 no.10
• /
• pp.1-8
• /
• 2021

Cylinder liners used in diesel engines of combat equipment are prone to cavitation due to wet cooling. The damage caused by erosion and corrosion due to cavitation has a fatal effect on the performance and lifespan of a diesel engine. Therefore, a study was conducted to improve the durability of cylinder liners. Two surface treatment techniques were proposed: nitriding and chrome plating. It was observed that the amount of erosion on the surface of nitride-treated cylinder liners was high because the surface-treated part eroded due to its weak impact resistance against the bubble explosion generated by cavitation. In contrast, the chrome-plated cylinder liner had a lower amount of erosion among the specimens subjected to the accelerated test. These results verified that the resistance of chrome-plated liners against cavitation is high. Therefore, it can withstand the impact of bubble explosion. If the chrome plating thickness is set with reference to the KS standard, an exceptional durability of abrasion, wear resistance, and corrosion resistance can be obtained. If the thickness is set between 120~250㎛, it is expected that the durability of the cylinder liner can be improved. Although a recovery method for corroded cylinder liners is suggested, the proposed method has an inherent risk of crack generation. Therefore, further research is required to solve this problem.

• International Journal of Automotive Technology
• /
• v.6 no.1
• /
• pp.1-8
• /
• 2005

Recently, the HSDI (High Speed Direct Injection) diesel engine has been spotlighted as a next generation engine because it has a good potential for high thermal efficiency and fuel economy. This study was carried out to investigate the in-cylinder flow characteristics generated in a HSDI diesel engine with a 4-valve type cylinder head. The four kinds of cylinder head were manufactured to elucidate the effect of intake port geometry on the in-cylinder flow characteristics. The steady flow characteristics such as coefficient of flow rate $(C_{f})$, swirl ratio (Rs), and mass flow rate (m,) were measured by the steady flow test rig and the unsteady flow velocity within a cylinder was measured by PIV. In addition, the in-cylinder flow patterns were visualized by the visualization experiment and these results were compared with simulation results calculated by the commercial CFD code. The steady flow test results indicated that the mass flow rate of the cylinder head with a short distance between the two intake ports is $13\%$ more than that of the other head. However, the non-dimensional swirl ratio is decreased by approximately $15\%$. As a result of in-cylinder flow characteristics obtained by PIV and CFD calculation, we found that the swirl center was eccentric from the cylinder center and the position of swirl center was changed with crank angle. As the piston moves to near the TDC, the swirl center corresponded to the cylinder center and the velocity distribution became uniform. In addition, the results of the calculation are in good agreement with the experimental results.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.15 no.1
• /
• pp.99-105
• /
• 2007

It is very important to clarify the 3-D angular flow characteristics of in-cylinder bulk motion in the developing process of variable induction system. In-cylinder flow induced by variable induction system is very complex, so we can not describe the in-cylinder bulk flow characteristics using the conventional swirl or tumble coefficient. In this study, we introduced the new 3-D angular flow index, angular flow coefficient($N_B$), for in-cylinder bulk flow characteristics. And also, to confirm the index, we carried out the steady flow rig test for intake port of test engine varying valve lift on the test matrix.

• Tribology and Lubricants
• /
• v.22 no.3
• /
• pp.155-163
• /
• 2006

Ring, groove and cylinder bore wear may not be a problem in most current automotive engines. However, a small change in ring face, groove geometry and cylinder bore diameter can significantly affect the lubrication characteristics and ring axial motion. This in turn can cause to change inter-ring pressure, blowby and oil consumption in an engine. Therefore, by predicting the wear of piston ring face, ring groove and cylinder bore altogether, the changed ring end gap and the changed volume of gas reservoir can be calculated. Then the excessive oil consumption can be predicted. Being based on the calculation of gas flow amount by the theory of piston ring dynamics and gas flow, and the calculation of oil film thickness and friction force by the analysis of piston ring lubrication, the calculation theory of oil amount through top ring gap into combustion chamber will be set. This is estimated as engine oil consumption. Furthermore, the wear theories of ring, groove and cylinder bore are included. Then the each amount of wear is to be obtained. The changed oil consumption caused by the new end gap and the new volume of oil reservoir around second land, can be calculated at some engine running interval. Meanwhile, the wear amount and oil consumption occurred during engine durability cycle are compared with the calculated values. Next, the calculated amount of oil consumption and wear are compared with the guideline of each part's wear and oil consumption. So, the timing of part repair and engine life cycle can be predicted in advance without performing engine durability test. The wear data of rings, grooves and cylinder bore are obtained from three engines before and after engine durability test. The calculated wear data of each part are turn out to be around the band of averaged test values or a little below.

• Journal of Korean Ophthalmic Optics Society
• /
• v.4 no.2
• /
• pp.39-43
• /
• 1999

In this study, It obtained results that the exact spherical diopter to practice test by using Cross cyliner lens and Red Green Card method. In the test used to the 1750 eyes of middle and high school students. The results was as follows ; 1. Using Cross cylinder lens method, I tested a exact spherical diopter after accommodation. At -0.25 Dptr the ratio of spherical Dptr error limits were measured as 58% and at -0.75 Dptr they were oppeared as 1%, at -1.00 Dptr they are not measured. In this method, the error limits of exact spherical Dptr was 91% from 0 Dptr to -0.25 Dptr. 2. Using Red Green Card method, they were measured as 45% at -0.25 Dptr. and measured as 20% at -0.50 Dptr. From the result of these test, Cross cylinder lens method was a better detailed method than Red Green Card method.

• Physical Therapy Rehabilitation Science
• /
• v.9 no.3
• /
• pp.197-200
• /
• 2020

Objective: The purpose of this study was to develop and investigate the feasibility of a sit-to-stand assistive chair using a pneumatic cylinder. Design: Cross-sectional study. Methods: The sit-to-stand assistive chair was developed to assist the sit-to-stand movement by rising up of the chair by a pneumatic cylinder. After the user is seated on the chair, if the pneumatic cylinder pulls the seat plate when standing up, the spring of the pneumatic cylinder, which has been stretched, assists in rising the rear end of the seat plate so that the user can stand conveniently and comfortably. A feasibility test was performed in 10 heathy adults. The electromyographic muscle activation of the trunk and lower extremity muscles was analyzed, which included the erector spinae, rectus abdominis, quadriceps, tibialis anterior, gastrocnemius when standing up from sitting using the developed chair and standing up without using the developed chair. Results: As a result, the sit-to-stand assistive chair using a pneumatic cylinder was developed. In the feasibility test, the use of the developed chair had a decrease in rectus abdominis, quadriceps, tibialis anterior activation compared to those who did not use the device in the healthy adults. Conclusions: The sit-to-stand assistive chair using a pneumatic cylinder may be helpful to reduce the activation of the rectus abdominis, quadriceps, tibialis anterior muscles when performing a sit-to-stand movement. Through the results, the efficacy of the sit-to-stand assistive chair can be confirmed. In the future, further studies are warranted to investigate for the safety and efficacy of its use in the elderly population or those who are disabled.

• Journal of the Korean Institute of Gas
• /
• v.11 no.2 s.35
• /
• pp.55-59
• /
• 2007

This paper presents the strength safety of a LPG cylinder, which is fabricated by a steel sheet forming and a welding technology. The strength safety of a cylinder is guaranteed by analyzing a stress distribution of a LPG cylinder structure using a finite element method. The FEM computed results indicate that the hydraulic test gas pressure of $31kg/cm^2$ generates a concentrated local stress near the upper round end plate, which exceeds the yield strength of a LPG cylinder. Thus, the current hydraulic test pressure may be rechecked and revised because this pressure increases the fatigue failure and decreases the lift of the pressure vessel. The normal operation and sealing gas pressures such as $9kg/cm^2\;and\;18.6kg/cm^2$ are relatively safe for a steel LPG cylinder.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.11 s.254
• /
• pp.1066-1073
• /
• 2006

Recently, because the variable induction systems are adopted to intake system, in-cylinder flow induced by induction system is very complex. Therefore it is very difficult to describe the in-cylinder bulk flow characteristics using the conventional swirl or tumble coefficient. In this study, in order to clarify the 3-D angular flow characteristics of in-cylinder bulk motion in the developing process of variable induction system, we introduced the new 3-D angular flow index, angular flow coefficient($N_B$) Finally, to confirm the index, we carried out the steady flow rig test for intake port of test engine varying valve lift on the test matrix.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.8 no.6
• /
• pp.51-59
• /
• 2000

In-cylinder spray flow motion plays an important in the adjustment of mixture preparation with a fundamental spray characteristics and in-cylinder flow field well in direct-injection gasoline engine. In this study, the fundamental spray characteristics such as mean drop size, velocity distribution, spray angle were measured and in-cylinder spray flow motion was visualized in order to optimize intake port, piston top land and combustion chamber shapes in the development stage of mass-produced G야 engine. For these experiments, the PDPA measurements and Mie scattering technique were used for detailed spray characteristics and in-cylinder spray motions were obtained by use of ICCD camera through the single-cylinder optical engine. From the experimental results, the test injector shows a good low-end linearity between the dynamic flow and fuel injection pulse width and the fuel spray of 20mm or less in SMD with good spray symmetry. In addition, the in-cylinder tumble flow has more effect on the homogeneous mixture formation than that of in-cylinder swirl flow at early injection mode and the in-cylinder swirl flow plays a better role of stratified mixture preparation than tumble flow at late injection mode.

• 유체기계공업학회:학술대회논문집
• /
• 2003.12a
• /
• pp.656-661
• /
• 2003

Modem reciprocating air compressors have tendency to a multi-stage W-type or V-type cylinder arrangement for the purpose of high outlet pressure, compactness and low vibration and noise. A valid counter weight calculation method using the complex expression is proposed for reducing the inertia forces of the compressor. Counter weight removes only 1st forward whirl component. Counter weight formulations are applied to the six various compressor structures which are (a) 1 cylinder single-throw crank shaft, (b) 2 cylinder single-throw crank shaft (c) 2 cylinder double-throw clank shaft, (d) 3 cylinder single-throw crank shaft, (e) 4 cylinder single-throw crank shaft and (f) 4 cylinder double-throw crank shaft. The improvement of performance is verified through available vibration test.