• 한국자동차공학회논문집
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• 제14권6호
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• pp.73-81
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• 2006

A commercial diesel engine was converted into a dedicated natural gas engine to reduce the exhaust emissions in a retrofit of a diesel-fueled vehicle. The cylinder head and piston were remodeled into engine parts suited for a spark ignition engine using natural gas. The remodeling of the combustion chamber changed the compression ratio from 21.5 to 10.5. A multi-point port injection(MPI) system for a dedicated natural gas engine was also adopted to increase the engine power and torque through improved volumetric efficiency, to allow a rapid engine response to changes in throttle position, and to control the precise equivalence ratio during cold-start and engine warm-up. The performance and exhaust emissions of the retrofitted natural gas engine after remodeling a diesel engine are investigated. The emissions of the retrofitted natural gas engine were low enough to satisfy the limits for a transitional low emission vehicle(TLEV) in Korea. We concluded that a diesel engine can be effectively converted into a dedicated natural gas engine without any deterioration in engine performance or exhaust emissions.

• 한국환경과학회지
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• 제14권1호
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• pp.15-22
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• 2005

Natural gas possesses several characteristics that make it desirable as an engine fuel; 1)lower production cost, 2)abundant commodity and 3)cleaner energy source than gasoline. Due to the physics characteristics of natural gas, the volumetric efficiency and flame speed of a natural gas engine are lower than those of a gasoline engine, which results in a power loss of $10-20{\%}$ when compared to a normal gasoline engine. This paper describes the results of a research to improve the performance of a natural gas engine through the modification and controls of compression ratio, air/fuel ratio, spark advance and supercharging and method of measuring flame propagation velocity. It emphasizes how to improve the power characteristics of a natural gas engine. Combustion characteristics are also studied using an ion probe. The ion probe is applied to measure flame speed of gasoline and methane fuels to confirm the performance improvement of natural gas engine combustion characteristics.

• 한국기계가공학회지
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• 제8권3호
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• pp.13-20
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• 2009

Development of a dynamic engine model is essential to predict and analyze of dynamic characteristics from a natural gas engine. Reducing the harmful exhaust emissions can be accomplished by a precise air-fuel ratio control. In this paper, the dynamic engine model was proposed and included mixture formation and intake process because the dynamic characteristics can be affected by the mixture components such as an air and a gaseous fuel. The air mass flow, the partial pressure ratio, and the gas constant are changed by variations of the components in the mixture formation and intake process. The dynamic engine model is applied to the natural gas engine for validation test. Experimental results show that the dynamic engine model is effective to predict the dynamic characteristics of the natural gas engine.

• 대한기계학회논문집
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• 제16권1호
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• pp.175-179
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• 1992

본 연구에서는 LPG 기관을 천연가스 이용기관으로 변경하고자 할 때 발생하는 출력 감소를 보안하기 우하여, 공기연료 혼합비 조절, 점화시기조절, 과급효과 방법에 의한 출력향상 효과를 파악하였다.

• 연구논문집
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• 통권23호
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• pp.121-126
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• 1993

In general, natural gas engine converted from gasoline engine has disadvantage of power decrease. In order to increase power output in natural gas engine, the improvement of in-cylinder flow motion has been believed as the most effective method. In this study, the geometry of combustion chamber in 4 valve DOHC natural gas engine is modified, and in-cylinder flow patterns are analyized. Also engine performance is evaluated according to the modification of in-cylinder flow motion.

• 한국가스학회지
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• 제17권6호
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• pp.20-26
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• 2013

본 연구에서는 기존 상용 12리터급 경유엔진을 베이스로, 천연가스 연료공급시스템을 추가함으로써 천연가스-경유연료를 동시에 사용하는 혼소엔진을 개발하였다. 전체적인 제어는 기존의 경유엔진 ECU를 이용하고, 추가적인 혼소 ECU를 제작하여 경유와 천연가스 연료가 최적으로 공급되도록 시스템을 구성하였다. 천연가스 연료는 MPI 방식으로 흡기메니홀드에 어뎁터를 이용하여 설치하였다. 혼소엔진의 실험결과, 경유엔진과 동등한 토크와 출력성능을 얻었으며, 배출가스 기준 또한 만족하였다. 전체적인 천연가스 연료 대체율은 70%이고, 주 사용영역에서는 약 76%의 대체율을 보였으며, 이로 인한 연료비용 절감효과는 전체 37% 및 주 사용영역에서는 40%를 얻었다.

• 한국기계가공학회지
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• 제8권2호
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• pp.83-89
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• 2009

An air-fuel ratio control is essential in reducing hazardous exhaust emissions from a compressed natural gas(CNG) engine, and can be accomplished by accurate control of gas injection flow. In this study, theoretical research was conducted on injection characteristics of a solenoid gas injector, and injection experiments for calibration and analysis were performed. Various factors for gas injection flow such as injection pressure, gas temperature, and supply voltage are studied. A dynamic flow equation of the natural gas was proposed on the basis of flow dynamics theories and results of the injection experiment. The verification of the dynamic flow equation of the solenoid injector was carried out with a large CNG-engine applied to an urban bus. Air-fuel ratio control experiments were conducted in both steady and transient state. Results of injection experiments for the solenoid injector and the CNG-engine was proved the control method proposed herein to be effective.

• 한국자동차공학회논문집
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• 제3권3호
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• pp.90-96
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• 1995

In general, natural gas engine converted from gasoline engine has disadvantage of power decrease. In order to increase power output in natural gas engine, the improvement of in-cylinder flow motion has been believed as the most effective method. In this study, the geometry of combustion chamber in 4 valve DOHC natural gas engine is modified, and in-cylinder flow patterns is analyized. Also engine performance is evaluated according to the modification of in-cylinder flow motion.

• 한국자동차공학회논문집
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• 제3권3호
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• pp.9-18
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• 1995

The substitution of conventional fuel oil by alternative fuels is of immense interest due to liquid oil shortage and requirements of emission control standard. Among the alternative fuels, natural gas may be the most rational fuel, because of its widespread resource and clean est burning. Meanwhile, engine simulation is of great importance in engine development. Hence a zero-dimensional combustion model was developed for dual-fuel system. Natural gas was injected directly into the cylinder and small amount of distillate was used to provide the ignition kernel for natural gas burning. The intake air and exhaust gas flow was modeled by filling and emptying method. Although the single zone approach has an inherent limitation, the model showed promise as a predictive tool for engine performance. Its simulation was also made to see how the engine performance was influenced by the fuel injection timings and amount of each fuel.

• 한국자동차공학회논문집
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• 제5권5호
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• pp.67-72
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• 1997

The purpose of this study os to investigate how the natural gas in fuel blend influences the polutant emission of diesel engine. Four stroke cycle single cylinder engine is used for this experiment and four kind of fuel blends were made. Fuel blends show four different torque ratios between diesel oil and natural gas, which are 4 : 0. 3 : 1, 2 : 2 and 1 : 3. The constituents of exhaust gases of engine are analyzed for every fuel blend. The experimental results say that the mixing of natural gas into diesel fuel is an very effective way to reduce the amount of soot in the exhaust gas.