Earticle

A gas forklift is often fueled by LPG or gasoline that emit toxic exhaust emissions, smoke, fumes and odors. These emissions become quite serious when forklifts are operated in confined areas. It is bad for the forklift operators as well as other workers who are inhaling the fumes. With cleaner burning natural gas, forklift operators and fellow workers are exposed to considerably less emissions. This study aims to develop the fuel system for the CNG-converted forklifts which is composed of hardwares and control algorithm for LPG forklift engine. The engine torque, power and emission in LPG fuel mode are measured to evaluate the difference of CNG engine performance. Based on the results, it is transparent that CNG-converted forklift is an very effective way to reduce the amount of CO, NMHC and NOX in the exhaust gas, which proves the developed control system is effective for CNG forklift engine.

CNG 차량의 경우 압력센서를 이용하여 CNG의 양을 계측하고 있다. 그러나 주변 환경 조건에 따라 정확한 양을 파악하는데 어려움이 있어 운전자에게 불안감을 조성하게 된다. 본 연구는 CNG 연료 시스템에서 CNG의 양을 정밀하게 측정하기 위한 기초 연구로써 CNG 연료량 검출 시스템을 모사하여 측정방법을 제시하고자 한다. 실험은 Type-3의 CNG 탱크에 초음파 센서를 적용한 연료량 검출 모사장치 구현하였다. 그리고 내부의 압력은 압축공기를 이용하여 100 bar 에서 0 bar 까지 5 bar 단위로 저감시키면서 초음파 센서의 수신 신호를 검증하였다. 그 결과 탱크 내 압력이 감소함에 따라 초음 파 센서의 출력 신호가 감쇠하는 것을 알 수 있었고, 다소 차이는 있었지만 선형성을 띄고 있는 것을 확인할 수 있었다.

The amount of CNG was measured using a pressure sensor in the case of CNG vehicles. However, the current measurement method causes anxiety to the driver because it is difficult to measure the detailed amount of CNG according to various environmental conditions. This study was performed to measure the amount of CNG in CNG fuel system, and presented the method of measurement by simulating the detection system of CNG. In this experiment, a detection simulator with an ultrasonic sensor in CNG tank of Type-3 was designed, and the reception signal of the ultrasonic sensor was verified by reducing the pressure from 100 bars to 0 bars (increment=5 bars) using compressed air. As a result, the output signal voltage of the ultrasonic sensor decreased as the pressure in the tank decreased, and the it was verified that the shape of the graph was linearity.

본 연구는 기체연료레벨 값에 대한 정밀도를 측정하기 위하여 초음파의 음향매칭에 관한 실험적인 분석을 수행한 것이다. 연구 모델은 송신과 수신에너지를 결정시키는 세라믹 어세이 (Ceramic Assay)의 구성요소에 의하여 설계되었다. 실험 장치로는 12V-DC 전원공급장치, Control T1 Board, 오실로스코프 (DSO1072B), 초음파 프로브 그리고 패턴테이블 (Pattern T)able이 사용되었다. 불감지영역에 대한 분석결과 최대피크지점인 2.9V의 시작점을 기준으로 D (0.180m) < E (0.184m) < B (0.204m) < A (0.234m) < F (0.244m) < C (0.247m) 모델 순으로 점차적으로 불감지폭이 증가되는 특성을 확인할 수 있었다. 실험결과로부터 매칭레이어 (Matching Layer)의 치수가 Ø21*3+2t로 설계된 모델에서 가장 우수한 지향 성 에너지를 생성할 수 있었다.

This work conducted the experimental analysis on ultrasonic acoustic matching in order to measure the accuracy of gaseous fuel level values. The experimental devices were used as 12V-DC supply, control T1 board, oscilloscope (DS01072B), ultrasonic probe and pattern table. The research models were designed by ceramic assay which can determine the transmitting and receiving energies. The result of the ringing area could verify the increased characteristics in the order of D (0.180m) < E (0.184m) < B (0.204m) < A (0.234m) < F (0.244m) < C (0.247m) models based on initial 2.9V of the maximum peak voltage. From the experimental results, the model designed by Ø21*3+2t of the matching layer was notable in that the most outstanding directivity energy could be created.

본 연구는 송·수신 초음파 센서를 이용하여 CNG 탱크에서의 정밀한 연료량을 측정하기 위한 기초 연구로써 탱크 내부 압력 및 초음파 센서의 접촉면 변경에 따른 수신감도를 분석하였다. 실험은 탱크와 센서의 접촉면을 점, 선, 면의 3가지 타입으로 변경하고 탱크 내부의 압력을 0 bar 부터 5 bar까지 1 bar 간격으로 충전하면서 측정을 진행하였다. 실험결과 탱크 내부의 압력이 증가함에 따라 초음파 센서의 수신신호 값이 감소하는 경향을 확인할 수 있었다. 또한 탱크와 센서의 접촉 면적이 증가할수록 수신 신호 값은 증가하지만, 노이즈 또한 증가하는 것을 확인 할 수 있었다. 이와 같은 실험 결과 초음파 의 투과 특성을 이용하여 탱크내부의 기체 연료량을 측정할 수 있을 것으로 판단되며, 센서의 접촉면 변경을 통해 정밀성을 향상시킬 수 있을 것으로 판단된다.

This paper is studied, as basic research for measuring the accurate fuel amount of the CNG tank by using the transmit-receive ultrasonic sensor, the receiving sensitivity according to changed the pressure inside the tank and the contact surface of the ultrasonic sensor is analyzed. Measurement was carried out while changing the contact surface of the tank and the sensor to three shapes of Point, Line, and Surface and charging the pressure in the tank at an interval of 1 bar from 0 bar to 5 bar. Experiment results, as the pressure in the tank increased the tendency of the received signal value of the ultrasonic sensor to decrease was confirmed. As the contact area between the tank and the sensor increased, the value of the received signal increased, but the noise also increased. The results of experiment, it is judged that accuracy can be improved by changing the contact surface of the sensor.

The safety at this study is investigated by flow or stress analyses due to configuration or installation direction of fuel tank in the existing CNG bus. In case of the lower ceiling with sharp type, the equivalent stress due to the explosion of fuel tank is less than the type of flat or arc. it becomes safer on passenger. In case of the installation direction of fuel tank in the existing CNG bus, the stress applied on the lower ceiling at transverse direction becomes less than at longitudinal direction. It is more stable on the safety of passenger. The harm on the explosion accident can be prevented by use of the analysis result at this study.

In order to satisfy the strengthening automobile exhaust gas regulation and CO2 regulation, the development of eco-friendly vehicles is actively progressing. To cope with these regulations, research on alternative fuel vehicles is being actively conducted. Alternative fuels are one of the best ways to reduce dependence on fossil fuels and respond to emissions and CO2 regulations. Natural gas, one of many alternative fuels, contains methane (CH4) as a main component and has abundant reserves, so it is attracting attention as a fuel that can provide stable long-term supply by replacing fossil fuels. In addition, natural gas has a high octane number, so there is room for improvement in combustion characteristics when used in SI engines, and it has the advantage of reducing harmful emissions and carbon dioxide (CO2) compared to conventional fossil fuels. When using a low-pressure injector in a turbo engine, it is difficult to secure the flow rate of fuel because the pressure difference between the injector and the manifold is small. Therefore, it is necessary to develop a high-pressure injector to improve this. Natural gas is a gaseous fuel and should be developed in consideration of compressible flow, Although the use of a CNG high-pressure injector is required, it is difficult to stabilize the flow due to the Mach disk and shock wave interference caused by compressible flow. If the flow is not stabilized, it is difficult to precisely control the flow. Therefore, it is necessary to develop an injector in consideration of flow characteristics. In this paper, the flow analysis according to the shape change of the injector was conducted to improve the fuel flow rate injected from the 800 kPa high pressure CNG injector.

According to industrialization and urbanization the number of increasing cars is attributable to an explosive increase of the vehicle emissions. In this study, in consideration of the population and local transportation characteristics of South Chungcheong Province the environmental and economic cost-benefit analyses are performed to evaluate whether the CNG bus conversion gives what kind of effects. Based on the analysis result the expansion and distribution plan of CNG bus is proposed for South Chungcheong Province, and the local supply policy model is also proposed considering the acquisition and management of the economic situation of CNG charging infrastructure and the small transportation companies.

본 연구는 축산분뇨 중 마분(馬糞)을 이용한 에너지생산을 위한 설비시설도입의 경제성과 이로 인한 연관 산업 파급효과를 리온티에프 역 행렬분석으로 검증하였다. 본 연구는 다음과 같은 점에서 기존연구와 구별된다. 우선, 국내에서 한 번도 다루어지지 않은 말의 분뇨를 이용한 전기와 수송연료생산에 관하여 다루었다. 둘째, 마분 에너지 화를 위한 설비시설에 대한 투자로 인한 산업파급효과뿐만 아니라 이에 대한 비용과 편익분석을 통해 사업성(경제성)분석을 동시에 하였다. 셋째, 공학적, 생화학적 공정뿐만 아니라, 경제적 분석을 학제적으로 접근하였다. 연구의 결과 마분의 에너지 화는 생산·부가가치·고용유발효과를 발생시키고 경제성이 있는 것으로 나타났다. 본 연구의 파급효과와 경제성분성은 넓게는 신재생에너지 정책을 추진하는 산업통상자원부를 비롯한 관련부처의 정책입안에 기초자료로 사용될 수 있고, 좁게는 말 산업 육성법에 따라 말 산업육성정책을 추진하는 각 지자체와 한국마사회, 농림축산식품부 등의 사업추진과정에서 말 분뇨처리정책, 일반 말 사육농가의 축산분뇨처리의 수익성검토에 이용될 수 있 수 있다 하겠다.

This study tried to see whether horse manure energization using anaerobic digesting technology can make economic spillover to employment and linkage industry. The result showed that adopting energy producing technology from horse manure can make economic spillover to backward and downstream industries supplying process equipment and service. And also find that horse manure energization substitutes crude oil import for foil fuel electric generation. Furthermore research shows the feasibility of commercialization of the individual and cooperate level and also prove that it can obtain CERs(Carbon Emission Right). This study is distinctive from precedent studies in three aspect, First study deals with horse manure which is has rare statistic data and never been dealt with in Korea. Second, Using Interdisciplinary research approach to agriculture, Engineering, Economic, Third, Applying input-output table to estimate spillover effect at the same time Benefit Cost Analysis for commercialization feasibility.

Compressed natural gas has various advantages as an automotive fuel compared to that of gasoline and diesel. Natural gas is economical, has better knock resistance, a wider range of flammable air fuel ratio, as well as lower carbon monoxide, carbon dioxide and hydrocarbon emissions.In CFD calculation, the comparison with optical data shows a good agreement in terms of jet penetration and overall evolution for all the cases examined here. From these results, CFD proves to be a useful tool to optimize injection against environmentalparameters and nozzle configuration in order to increase efficiency and reduce the emissions in a CNG-fuelled DI engine.

There are two types of fuel supply method in CNG vehicles. One is premixed ignition and the other is gas-jet ignition. In premixed ignition, the fuel is introduced with intake air so that homogeneous air-fuel mixture may form. The ignitability of this method depends on the global equivalence ratio. In gas-jet ignition, CNG is introduced directly into the engine combustion chamber. The overall mixture is stratified by retarded fuel injection. In this study, a visualization technique was employed to obtain fundamental properties regarding overall mixture formation and combustion characteristics of direct injected CNG fuel inside a constant volume chamber and engine. For gas-jet visualization, Schlieren high speed imaging is used with the effects of ambient pressure and impingement wall on mixture formation being investigated.

A CNG/diesel dual-fuel engine uses CNG as the main fuel and injects a small amount of diesel as an ignition priming. This study proposed the modification of the existing diesel engine into a dual-fuel engine that injects diesel with a high pressure by common rail direct injection (CRDI) and by injecting CNG at the intake port for premixing. And experiment was progressed for understanding about effect of CNG mixing ratio. The CNG/diesel dual-fuel engine showed equally satisfactory coordinate torque and power regardless of CNG mixing ratio. The PM emission was low at any CNG mixing ratio because of very small diesel pilot injection. In case of NOx and HC, high CNG mixing ratio showed low NOx and HC emissions at low speed. At medium & high speed, low CNG mixing ratio showed low NOx and HC emissions. Therefore, it would be optimized by controlling CNG mixing ratio.

2012년 7월부터 우리나라 천연가스 열량에 대한 기준이 기존의 표준열량제에서 열량범위제로 변경되면서 가정이나 산업체로 공급되는 가스 열량 변화가 가스기기 성능에 미치는 영향을 규명하고자 하는 노력이 이루어지고 있다. 특히 천연가스를 주 연료로 사용하는 열병합 발전용 엔진의 경우 이러한 열량 변화에 의해 엔진 성능 전반에 걸쳐 영향이 있을 것으로 예상된다. 따라서 이번 연구에서는 열량범위제를 고려한 CNG 열량 변화가 디젤-CNG 혼소엔진의 효율 및 연소특성에 미치는 영향에 대해 조사하였다. CNG 모사 연료의 발열량은 $10,400kcal/Nm^3$에서 $9,400kcal/Nm^3$까지 질소 가스를 CNG에 희석하는 방식으로 변경을 하였다. 우선 디젤연료의 분사시기와 혼소율을 80%로 고정한 조건에서 가스연료의 발열량 변화가 엔진 효율 및 출력 변화에 미치는 영향을 살펴보았으며, 열방출율 및 연소압력 등의 변화를 측정하였다. 실험 결과로부터 가스 열량이 낮아질수록 엔진 출력과 효율이 모두 감소함을 알 수 있었으며, 점화지연시간과 연소기간은 가스 열량 감소에 관계없이 일정하게 유지되는 반면 최대연소압력은 낮아짐을 볼 수 있었다.

In this study, a dual fuel engine fueled with natural gas and diesel was tested to investigate the effects of heating value variation of CNG fuel. CNG substitution rate which is defined as the ratio of CNG and diesel supplied in a heating value basis was fixed at 80%. The higher heating value was varied from $10,400kcal/Nm^3$ to $9,400kcal/Nm^3$ by mixing nitrogen gas with pure CNG and diesel fuel was injected at a fixed injection timing. The engine test results showed that thermal efficiency and power output were decreased as the heating value of mixed CNG fuel was decreased. And the peak cylinder pressure was also decreased but the ignition delay time and the combustion duration and timing were almost same.

전 세계적인 천연가스 저열량화 추세에 따라 우리나라 천연가스 열량 기준이 기존의 표준 열량제에서 보다 유연한 열량범위제로 개선되었다. 이 같은 변화는 가정이나 산업체 전반에 걸쳐 가스기기 성능에 직접적인 영향을 미치기 때문에 이를 규명하고자 하는 연구가 필요하다. 특히 열병합 발전용 엔진으로 사용되는 디젤-CNG 혼소엔진의 경우 도시가스를 주 연료로 사용하기 때문에 발열량 변화는 발전 사업자의 수익성 확보와 연관되는 중요한 사안이다. 따라서 본 연구에서는 열량범위제 내에서 허용하는 CNG 발열량 변화가 디젤-CNG 혼소엔진의 배기특성에 주는 영향에 대해 조사하였다. 도시가스 발열량 변화를 모사하기 위해 열량 범위 상한선인 $10,400kcal/Nm^3$의 CNG 연료에 질소를 희석시켜 발열량을 $10,400kcal/Nm^3$에서 $9,400kcal/Nm^3$까지 변경하였다. 혼소율 80% 조건에서 디젤 연료 분사 시기는 16 CAD BTDC, 분사압력은 110 MPa로 고정하고 엔진회전수 및 토크는 1800 rpm/500 Nm으로 설정하여 시험을 수행하였다. 엔진시험 결과 발열량이 감소할수록 불완전연소가 증가하여 THC, $CH_4$ 및 CO 배출량은 증가하는 반면 NOx 배출량은 감소함을 확인하였다. 그리고 이 같은 결과를 바탕으로 배기 특성 변화에 대해 대응할 수 있는 방안에 대해 고찰하였다.

In this paper, purpose of study is emissions characteristics according to effects of heating value variations of CNG fuel in a dual-fuel engine fueled by diesel and natural gas. For heating value variation of CNG fuel, nitrogen gas was mixed with pure CNG fuel. So the higher heating value was changed from $10,400kcal/Nm^3$ to $9,400kcal/Nm^3$. Under one condition of CNG substitution rate was fixed at 80%, diesel fuel was injected at a fixed injection timing of 16 CAD BTDC and fuel pressure was also fixed at 110 MPa. The condition of tested engine was 1800 rpm and 500Nm. Emissions were sampled in exhaust pipe was located at downstream turbocharger. As a result, emissions characteristics were checked in heating value variations of CNG fuel with mixed nitrogen gas THC, $CH_4$ and CO emissions decreased and NOx and $CO_2$ increased.

There are about 38,977 CNG cars and 247 natural gas vehicle charging stations in operation in order to improve the urban air environment. With the introduction of natural gas vehicles, the atmospheric environment, which was the main cause of air pollution in the metropolitan area, was remarkably improved. However, unlike these positive effects, CNG bus accidents, which occurred more than 10 times since 2005, have caused concern among the majority of citizens using public transportation. It is necessary to make a judgment on the feasibility and future direction of CNG pressure vessel safety management that can safeguard the safety of CNG pressure vessel at the time of starting. In this study, we investigates production and use of CNG vessel, the current status of safety management of CNG bus transportation companies & charging stations and then proposes measures to prevent accident recurrence and safety management based on the actual situation investigation and analysis.

In this study, feedback logic using dual O₂ sensor values were developed to increase the purification capability of a three-way catalyst (TWC) in a compressed natural gas (CNG) engine. A heavy-duty inline 6-cylinder engine was used and the CNG was supplied to the engine through a mixer. This study consists of two main parts, namely, the proportional integral (PI) control with a front O₂ sensor and the feedback control with dual O₂ sensors. In the PI control experiment, effects of various parameters, such as P gain, I gain, and lean delay, on the TWC capability were identified. Based on the results of the PI control experiment, the feedback logic using dual O₂ sensor values were developed. In both cases, the nitrogen oxides (NO_X) emissions were nearly zero. However, the carbon monoxide (CO) emissions were reduced significant in the feedback logic with dual O₂ sensors than in the PI control with the front O₂ sensor.

국내 CNG Bi-fuel Kit를 개조한 차량들은 대부분 Diaphragm 감압방식을 적용한 기계식 레귤레이터를 장착하여 운행 중에 있다. 하지만 Diaphragm의 재질 특성 및 기계식 압력제어 방식의 특성 상 다양한 문제점들이 발생되고 있으며, 이를 개선하기 위한 연구들이 진행되고 있다. 본 연구에서는 CNG 차량용 레귤레이터의 압력제어방식에 따른 성능특성 확인 및 비교 분석 진행을 통해 개선방안을 도출하고자 하였다. 실험 결과에 따르면 Diaphragm을 적용한 감압방식이 Piston을 적용한 방식보다 일반적인 성능에서 유리하였으나 주변 온도환경 변화에 따른 변동 폭이 큰 것을 확인하였다. 또한 전자식 압력제어를 통해 레귤레이터의 일반적인 성능을 향상시킬 수 있음을 확인하였다.

The domestic vehicles remodeling the "CNG Bi-fuel Kit" are mostly in operation with installing the mechanical regulator applying the Diaphragm. However, due to the material characteristics of Diaphragm and characteristics of mechanical pressure control method, various problems are happening. This study tries to deduce the improvement plan through the checking of performance characteristics according to the pressure control method of CNG regulator and progress of comparative analysis. According to the test result, the decompression method applying the Diaphragm has advantage compared to the method applying the Piston. Furthermore, it was confirmed that through the electronic pressure control, it is possible to improve the general performance of the regulator.