• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1141-1148
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• 2008

One of the methods to increase the efficiency of an engine is to expand pressures obtained from combustions equal to the pressure of atmosphere as much as possible and then convert thermal energy into mechanical energy also as much as possible. In this research, the Diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting Diesel engines to the Atkinson cycle, and general cycle features were analyzed after comparing these two cycles. In the case of fuel air the Diesel-Atkinson cycle considering intake and exhaust similar to real cycles, the value of thermal efficiency and average effective pressure increased, though their values were smaller than those of standard air amount cycle, when expansion compression ratio increased. When normal Diesel engines of which compression stroke and expansion stroke are all the same, was converted to the Atkinson cycle by changing the time of intake value close, combustion pressure reduced due to reduced expansion compression ratio and intake air amount due to decreased effective cycle volume.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.10
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• pp.1147-1154
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• 2004

This paper is the third of several companion papers which compare the method of Air-Fuel ratio determination. In the previous works, Eltinge chart was expanded to arbitrary fuel composition as a reference exhaust composition. The compensation of unburned hydrocarbon in Eltinge chart and comparison of Spindt and Eltinge method were also discussed. In addition to Eltinge and Spindt's one, however, there are many methods which calculate Air-Fuel ratio from exhaust emission. Among these methods, carbon balance and oxygen balance are widely used in practice. In some applications, linear formula from statistical method is being used in the field due to its simplicity and convenience. In this paper, these various methods are evaluated and compared with Eltinge results and new linear formula is proposed for the gasoline fuel. The results show that the corrected carbon balance equation has excellent agreement with Eltinge and Spindt's one. On the other hands, the oxygen-balanced formula has a limitation according to the mixture state and AFR. For gasoline fuel, newly proposed linear equation has good compatibility with Eltinge and Spindt up to AFR 17.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.1
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• pp.37-43
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• 2010

The purpose of this paper is to investigate the effect of air-fuel ratio on the combustion and emissions characteristics of spark ignition (SI) gasoline engine fueled with bio-ethanol. A 1.6L SI engine with 4 cylinders was tested on EC dynamometer. In addition, lambda sensor and lambda meter were connected with universal ECU to control the lambda value which is varied from 0.7 to 1.3. The engine performance and combustion characteristics of bio-ethanol fuel were compared to those obtained by pure gasoline. Furthermore, the exhaust emissions such as carbon monoxide (CO), unburned hydrocarbon (HC), oxides of nitrogen ($NO_X$) and carbon dioxide ($CO_2$) were measured by emission analyzers. The results showed that the brake torque and cylinder pressure of bio-ethanol fuel were slightly higher than those of gasoline fuel. Brake specific fuel consumption (BSFC) of bio-ethanol was increased while brake specific energy consumption (BSEC) was decreased. The exhaust emissions of bio-ethanol fuel were lower than those of gasoline fuel under overall experimental conditions. However, the specific emission characteristics of the engine with bio-ethanol fuel were influenced by air-fuel ratio.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.6
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• pp.96-103
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• 2014

Liquefied Petroleum Gas(LPG) has attracted attention as a alternative fuel. The lean-burn LPG direct injection engine is a promising technology because it has an advantage of lower harmful emissions. This study aims to investigate the effect of combustion strategy and excess air ratio on combustion and emission characteristics in lean-burn LPG direct injection engine. Fuel consumption and combustion stability were measured with change of the ignition timing and injection timing at various air/fuel ratio conditions. The lean combustion characteristics were evaluated as a function of the excess air ratio with the single injection and multiple injection strategy. Furthermore, the feasibility of lean operation with stratified mixture was assessed when comparing the combustion and emission characteristics with premixed lean combustion.

• International Union of Geodesy and Geophysics Korean Journal of Geophysical Research
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• v.22 no.1
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• pp.24-32
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• 1994

A special upper-air observation including airsonde and pibal observations was performed to investigate the characteristics features of the vertical distribution of the meteorological elements over Taegu on a selected clear day of each season from October 1991 to August 1992. The diurnal and seasonal variations of the vertical profiles of air temperature and mixing ratio were obtained from airsonde observations and wind speed and direction from pibal observations. The results of these special upper-air observations are as follow : The diurnal variation of the vertical distribution of air temperature reveals the characteristic features associated with the atmospheric boundary layer. All case days, except for the summer season, show upper-level inversion layer which influenced by surface high, and surface inversion layer produced by radiative cooling. The diurnal variation of mixing ratio shows the maximum vale at 1500 LST in both the upper and low levels, and is larger on the lower level than the upper level. The mixing ratio of the lower level is larger than that of the upper level. On the average the mixing ratio decrease with the height, and is the wettest on the summer case day and the driest on the winter case day. The diurnal variation of the wind velocity and direction are variable in the lower level with time and height, while they are steady in the upper level. On the average, the wind direction is southerly or southeasterly for the summer case day, westerly or northwesterly for the spring and fall case days, and northerly or northwesterly for the winter case day.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.74-82
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• 2004

Planar laser-induced fluorescence(PLIF) has been widely used to obtain two dimensional fuel distribution. Acetone PLIF is chosen because fluorescence signal from acetone as a fluorescent tracer is less sensitive to oxygen quenching than other dopants. Acetone PLIF is applied to measure quantitative air excess ratio distribution in an engine fueled with LPG. Acetone is excited by KrF excimer laser (248nm) and its fluorescence image is acquired by ICCD camera with a cut-off filter to suppress Mie scattering from the laser light. For the purpose of quantifying PLIF signal, an image processing method including the correction of laser sheet beam profile is suggested. Raw images are divided by each intensity of laser energy and profile of laser sheet beam. Inhomogeneous fluorescence images scaled with the reference data, which is taken by a calibration process, are converted to air excess ratio distribution. This investigation shows instantaneous quantitative measurement of planar air excess ratio distribution for gaseous fuel.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.1
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• pp.17-25
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• 2008

To achieve the unidirectional airflow in a cleanroom, we need to predict accurately the static pressure losses at the lower plenum and to control properly the opening pressure ratio of access floor panels based on these pressure losses. At first, the present study proposed a correlation to predict the velocity distribution at the lower plenum, because the accuracy to predict pressure losses at the lower plenum depends on how to calculate the velocity correctly against the inner structures at the lower plenum. In the second place, this study proposed correlations which considered the effect of inner structures such as columns, ducts and equipments at the lower plenum on pressure losses. In order to test the accuracy of these correlations, we compared air flow patterns before regulating the opening ratio of access floor with those after regulating. Results after regulating the opening ratio of access floor show good unidirectional uniform airflow pattern. So the present method can be used as an important tool to control the air flow in a cleanroom.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.11
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• pp.923-932
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• 2006

In this paper, reentering ratio and cooling capacity of individual cooling towers arrayed on a building roof were studied by a numerical method. The number of 16 cooling towers were divided into 4 banks. It was considered the summer prevailing wind characteristics as west wind and south wind of 5 m/s. It was also considered the roofwall types as the curtainwall and the louverwall that had the outdoor air intake louver in the curtainwall. In this case, the louver was suggested as the solution that could prevent reentering phenomenon due to recirculation and interference of the discharge air. In the case of the curtainwall, the averaged reentering ratio are predicted 13.3% and 24.4% for the west and south wind of 5 m/s, respectively. In the case of the louverwall, the averaged reentering ratio are predicted 2.5% and 9.7% for the west and south wind of 5 m/s, respectively. Therefore, the louverwall is a appropriate solution for reducing the reentering phenomenon.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.23 no.2
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• pp.77-83
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• 1994

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.44-52
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• 1993

In this study, the characteristics of decreasing exhaust gas of diesel engine was examined in dual fuel method by using commertial LPG for automotive. LPG was supplied to engine intake port by fumigation method and flow rate was controlled by using the needle valve. LPG supply ratios were 0, 20, 30% of total fuel amount to be supplied to engine by mass base. We investigated the effect of LPG supply ratio on exhaust gas concentrations related to excess air ratio and engine load at 1600, 1800, 2000 rpm. Soot concentration decreased about 30% in proportion to the increase of the LPG supply ratio. NOx concentration decreased in proportion to the increase of the LPG than diesel only and the increase rate was higher at low engine load. BSFC(Brake specific fuel consumption) was lower in proportion to the increase of the LPG supply ratio at high engine load and to the decrease of LPG supply ratio at low engine load.