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가변 밸브 timing과 duration이 가솔린 엔진 연비 특성에 미치는 영향
김재헌(Jaeheun Kim),배충식(Choongsik Bae),최명식(Myungsik Choi) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11
An experiment was conducted to study the effects of valve events on the engine performance. A prototype gasoline direct injection engine was used to realize the independent control of four valve event parameters, namely intake valve opening (IVO), intake valve closing (IVC), exhaust valve opening (EVO), and exhaust valve closing (EVC). The EVO timing contributed to the optimization of the blowdown during the end of the exhaust stroke and the exhaust pumping work. The retardation of IVC timing allowed the engine to operate with wider throttle angle at fixed load condition, which reduced the pumping work significantly. The valve overlap was controlled with IVO and EVC. The pumping work decreased when the valve overlap position laid at the vicinity of top dead center (TDC) with sufficient valve overlap duration. The IVC and EVO played a dominant role in optimizing the fuel consumption characteristics compared to IVO and EVC. The IVC and EVO should be optimized in prior to the optimization of IVO and EVC.
소형 리니어 엔진에서 LPG와 수소 연료에 따른 운전 특성 비교
김재헌(Jaeheun Kim),배충식(Choongsik Bae),김강출(Gangchul Kim) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
A prototype of small-sized, spark ignition free piston engine combined with a linear alternator was designed and built, which is used to produce electric power for portable usage. Engine performance including indicated mean effective pressure and piston velocity were compared for hydrogen and liquefied petroleum gas. The total lower heating value of two fuels per unit time was maintained equal to compare the combustion and operation characteristics of each fuel. Effects of alternator load to the engine performance were observed. The combustion characteristics such as heat release rate, cycle-tocycle variation and the power output of two fuels were studied. Hydrogen resulted in stable operation due to its faster flame speed and wider flammability range, while LPG showed higher cycle-to-cycle variation and misfire in some cycles. Under the same alternator load, hydrogen resulted in better power output than LPG, because hydrogen had more energy released from the fuel than LPG, which is modified from the accumulated heat release analysis. As the load increased, operation with LPG showed higher possibility of engine operation failure due to misfire, which is mainly caused by the inappropriate combustion condition accompanied by the piston motion. Meanwhile, hydrogen showed a large operation range with various load conditions.
Late Intake Valve Closing (LIVC) 전략이 DME 압축착화 엔진 연소에 미치는 영향
김재헌(Jaeheun Kim),배충식(Choongsik Bae) 한국자동차공학회 2012 한국자동차공학회 부문종합 학술대회 Vol.2012 No.5
The effective compression ratio reduction by means of late intake valve closing (LIVC) strategy was applied in a DME compression ignition engine to investigate its potential effects on the engine performance and emissions. The single injection timing of the DME was varied through the beginning of the compression to the end of compression stroke. The DME was injected directly into the cylinder with an injection pressure of 60 MPa. Two different intake valve closing (IVC) conditions were investigated, namely base IVC timing of 28 deg ABDC (after bottom dead center) and LIVC timing of 43.9 deg ABDC. The IMEP characteristics with respect to the injection timing at two different IVC timings showed a similar trend with only a phase shift towards the advanced injection timing. The reduction in the compression ratio had resulted in lower compression pressure and temperature than those of base IVC timing, so the ignition delay was increased and the overall heat release rate was retarded to the later crank angle. The combustion duration was also lengthened for the LIVC timing due to the reduced magnitude of heat release rate and reduced in-cylinder temperature. The NOx emission was reduced by 10% due to the reduced in-cylinder combustion temperature. The prolonged ignition delay which enhanced the mixture homogeneity was also considered to contribute on the reduction of NOx emission. It showed potentials that the NOx emissions can be reduced while maintaining the engine power output through LIVC strategy. The HC and CO was low at the injection timing where the NOx emission was the maximum due to the high temperature atmosphere for the oxidation of HC and CO. The soot formation was low due to the intrinsic characteristics of DME, and the effect of IVC timing on soot variation was not clearly observed. The maximum pressure rise rate was lower for the LIVC timing condition. Prolonged combustion period and reduced magnitude of heat release rate caused a slower pressure rise. However, the absolute value of the maximum pressure rise rate was still high due to the single injection, and it needs to be further improved.
프로판을 이용한 소형 리니어 엔진의 효율 및 운전 특성
김재헌(Jaeheun Kim),박정서(Jungseo Park),배충식(Choongsik Bae) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
The operating characteristics and efficiency of a small-sized linear engine fueled with propane for generating electricity was investigated. The bore and stroke of the engine was 20 ㎜ and 19 ㎜, respectively, resulting in total displacement of 12 ㏄ with 2 cylinders. Spark ignition system was adopted, and the mixture of propane and air was supplied to the combustion chamber. The pressure and the equivalence ratio of the mixture were varied to investigate the operating speed and combustion characteristics. Displacement sensor was used to measure the displacement of the piston and the velocity data was further derived. Pressure data inside the combustion chamber was measured with pressure transducer to study the combustion. Under the idling condition, the variation of the operation frequency was not obvious as the variation of the mixture conditions, and the operating frequency maintained around the value of 50 ㎐. The combustion of each cycle showed instability according to the variation of the IMEP(Indicated Mean Effective Pressure), and eventually resulted in large cyclic variation. The main reason of the instability was due to the uneven amount of mixture trapped in the cylinder during the scavenging process. Also, low overall fuel conversion efficiency of the engine was observed due to the low scavenging efficiency of the 2-stroke engine and certain amount of short-circuited fuel.
2행정 리니어 엔진에서 스파크 타이밍과 당량비에 따른 피스톤 운동의 변화
김재헌(Jaeheun Kim),장진영(Jinyoung Jang),박정서(Jungseo Park),배충식(Choongsik Bae) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
A small-bore 2-stroke linear engine has been designed to generate electricity linked with a linear alternator. In order to precisely control the operating frequency of the piston, the velocity of the piston accelerated by the combustion pressure was studied. The experiment was designed to investigate how some parameters ? mainly spark timing (ST) delay and air/fuel equivalence ratio - influence the combustion. In this study, one side of the engine cylinder was used for the combustion and the other cylinder was used to accelerate the piston to the designated compressing velocity, to exactly examine the influence of the 2 parameters to the velocity change of the piston. The size of the piston diameter is 10 mm and the maximum available stroke is 19 mm. Dynamic parameters such as displacement, velocity, and acceleration data were acquired, and pressure data had also been analyzed to see the maximum peak pressure of the combustion. The indicated mean effective pressure (IMEP) was calculated to find out under which conditions the maximum work was done. The maximum IMEP was found as the spark timing delay increased, and the velocity increase had a similar increasing trend in response with IMEP.
LAS (Laser absorption scattering) 기법을 통해 다단 분사 전략이 디젤 분무 혼합기 형성 및 연소에 미치는 영향 분석
김재헌(Jaeheun Kim),Keiya Nishida 한국연소학회 2019 KOSCOSYMPOSIUM논문집 Vol.2019 No.5
The split injection strategy was investigated in a constant volume chamber under evaporating, but non-reacting condition. Laser absorption scattering (LAS) technique was used to acquire the mixture concentration measurement, using a diesel surrogate fuel consists of n-tridecane and 1-methylnaphthalene. The effects of split ratio and dwell time between two injection events were investigated. Three split ratios, namely 3:7, 5:5, and 7:3 were selected. The split ratio of 7:3 was the best among three conditions in terms of mixture formation process. The spray from the second injection of the split ratio of 7:3 showed adequate vapor penetration, so that the fuel could be positioned within the fuel lean region formed from the first injection. The intensity of the diffusion flame was also lower with the split ratio of 7:3, due to the greater portion of the premixed combustion occurred during the first injection.