• Journal of the Korean Institute of Gas
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• v.18 no.4
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• pp.13-20
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• 2014

In natural gas distribution system, gas pressure is regulated correspond to requirement using throttle valve which is releasing huge pressure energy as useless form. The waste pressure can be recovered by using turbo machinery devices such as a turbo expander. In this process, excessive temperature drop occurs due to Joule-Thompson effect during the expansion process. Installing natural gas boiler before or after the turbo expander prevents temperature drop. Fuel cell or gas engine hybrid system further improve the efficiency, but 1~2% of total transporting natural gas is used for operating the hybrid system. In this study, a heat pump system is proposed as a preheating device which can be operated without using transporting natural gas. Thermodynamic analysis on evaporating and condensing temperatures and refrigerants is conducted. Results show that R717 is proper refrigerant for the hybrid system with high COP and low turbine work within the defined operating conditions. In domestic usage in Korea, the heat pump system has more economic feasibility owing to natural gas being imported with a high price of LNG form.

• The Monthly Technology and Standards
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• s.16
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• pp.47-49
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• 2003

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.16-21
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• 2003

Natural gas is one of the promising alternative fuels because of the abundant deposits and the cleanness of emission gas. It can be used in conventional gasoline engine without major modification. Natural gas has some advantages than gasoline i.e. the high octane number, good mixing condition because of gas and wide inflamable limit. In the present study, a $1.8{\ell}$ conventional gasoline engine is modified for using the CNG as a fuel instead of gasoline. Performance and emission characteristics are compared between gasoline and CNG with 4 cylinder SI Engine which is controlled by programable ECU. Parameters of experimentation are equivalence ratio, spark timing and fuels. We analyzed the combustion characteristics of the engine using the cylinder pressure i.e. ignition delay, combustion duration and cycle variation. As a result, CNG engine shows lower exhaust emissions but brake torque is slightly reduced compared to gasoline engine. Overall combustion duration is longer than that of gasoline because of lower burning speed.

• Journal of the Korean Institute of Gas
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• v.22 no.6
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• pp.34-39
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• 2018

Natural gas is attracting attention as an alternative to existing fossil fuels. Natural gas has a high octane number. Therefore, knocking does not occur even if the compression ratio is increased, so that the thermal efficiency and the output can be improved. And it is relatively easy to apply the natural gas supply system to the internal combustion engine hardware system. In this study, a gasoline direct injection turbo engine was converted into a natural gas port injection type turbo engine. Therefore, the combustion and performance of the engine are measured and compared comprehensively in the region where the turbo operates.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1998.05a
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• pp.73-78
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• 1998

상용 IGCC발전소의 특징적 공정흐름에 대한 분석기술의 확보를 위해 PDU급 IGCC발전계통에 대한 성능평가와 NOx 배출에 대한 모델링을 수행하였다. 향후 IGCC발전소 건설시 선정가능성이 있는 4가지 가스화 공정에서 생산되는 석탄가스를 연료로 하고, 그 발전계통의 대상 가스터빈은 산업현장에서 사용되고 있는 GE사의 LM1600PA를 선정하였다. 석탄가스는 천연가스에 비해 가스터빈의 효율과 출력 상승을 가져오나, 이와 동시에 압축기 탈설계점 작동문제를 야기 시킬 수 있다. 또한 NOx 발생량은 석탄가스 연소시 급격히 증가하며, NOx 제어를 위해 질소분사가 이루어져야 함을 알 수 있었다.

• Journal of the Korean Institute of Gas
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• v.20 no.1
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• pp.7-12
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• 2016

Natural gas liquefaction process is essential to transport natural gas for long distances. Lots of compressors in this process are needed and the energy for these compressors can be supplied by drivers. Total driver cost can be changed by selecting various drivers. This study focused on the minimization of the driver cost to provide the energy to the compressors. Moreover, scenarios, extracting velocity is changed during whole operating period, are set with considering gas well capacity. The mathematical model was established by considering trade off relationship between the capital cost and the operating cost of the turbines. The model also considers the life time of the driver equipments. As the result, the driver cost of the optimized case was reduced by 6.4% than the base case.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.7
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• pp.625-638
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• 2014

In this study, the uncertainties in the critical flow functions (CFFs) calculated by the AGA8-dc equation of state were estimated. To this end, the formulas for enthalpy, entropy, and speed of sound, which are used in calculating the CFF, were expressed in the form of dimensionless Helmholtz free energy and its derivatives, and the uncertainty in Helmholtz free energy was inferred. To consider the variations in the compressibility-dependent variables induced by the variation (i.e., uncertainty) in compressibility, the form of the AGA8-dc equation was modified to have a deviation equal to the uncertainty under each flow condition. For each independent uncertainty component of the CFF, a model for uncertainty contribution was developed. All these changes were applied to GASSOLVER, which is KOGAS's thermodynamic database. As a result, the uncertainties in the CFF were estimated to be 0.025, 0.055, and 0.112 % at 10, 50, and 100 bar, respectively, and are seen to increase with the increase in pressure. Furthermore, these results could explain the deviations in the CFFs across the different labs in which the CFF international comparison test was conducted under the ISO management in 1999.

• Korean Chemical Engineering Research
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• v.51 no.1
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• pp.25-34
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• 2013

The paper reviews the state of art in the design of liquefaction processes for the production of liquified natural gas, and addresses key design aspects to be considered in the design and how these design issues are systematically reflected in industrial applications. Various design options to improve energy efficiency of refrigeration cycles are discussed, including cascaded or multi-level pure refrigeration cycles which are used for covering wide range of cooling temperature, as well as mixed refrigerant cycle which can maintain a simple structure. Heat integration technique has been used for graphically examining differences of commercial cycles discussed in this paper, while energy efficiency and economics of commercial liquefaction processes has been summarized. Discussion also has been made about how to select the most appropriate set of drivers for compressors used in the liquefaction plant.

• Journal of the Korean Institute of Gas
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• v.17 no.3
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• pp.27-32
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• 2013

Natural gas liquefaction process which is operated under cryogenic condition spends large amount of energy. Most of energy in the natural gas liquefaction process is consumed by compressors. Therefore, minimizing energy consumption of compressors is an important issue in process design and operation. Among various natural gas liquefaction processes, propane pre-cooled mixed refrigerant (C3MR) process consists of mixed refrigerant system and pure refrigerant system. In this study, to find the optimal design of pure refrigerant system, pure refrigerant cycle is simulated on different number of pressure levels and the necessary energy of each design is compared. After that, the driver selection model is applied to analyse each processes, which has different number of equipments, in terms of cost. As the result, the design using many equipments spends lower energy. Using this result, this study suggests standard of process design selection by the cost term.

• Journal of ILASS-Korea
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• v.28 no.2
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• pp.55-61
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• 2023

Natural gas is a high-octane fuel that is effective in controlling knocking combustion. In addition, as a low-carbon fuel with a high hydrogen-carbon ratio, it emits less carbon dioxide and almost no particulate matter compared to conventional fossil fuels. Stoichiometric combustion engines equipped with a three-way catalyst are useful in various fields such as transportation and power generation because of their excellent exhaust emission reduction performance. However, stoichiometric combustion engines have a disadvantage of lower thermal efficiency compared to lean combustion engines. In this study, a combination of high compression ratio and Atkinson cycle was implemented in a 11 liter, 6-cylinder, spark-ignition engine to improve the thermal efficiency of the stoichiometric engine. As a result, pumping and friction losses were reduced and the operating range was extended with optimized Atkinson camshaft. Based on the exhaust gas limit temperature of 730℃, the maximum load and thermal efficiency were improved to BMEP 0.66 MPa and BTE 35.7% respectively.