Feasibility of compression ignition for hydrogen fueled engine with neat hydrogen-air pre-mixture by using high compression

Lee, K.J.,Kim, Y.R.,Byun, C.H.,Lee, J.T. Pergamon Press ; Elsevier Science Ltd 2013 International journal of hydrogen energy Vol.38 No.1

Compression ignition of hydrogen engines with a homogeneous pre-mixture is a promising method to enhance the thermal efficiency as well as to reduce unique NO<SUB>x</SUB> exhausted from the engine due to spatial reaction of the mixture. However, hydrogen gas has a relatively high self-ignition temperature. Therefore, compression ignition for a neat hydrogen-air pre-mixture is considered impossible to achieve without additives. Research on this has not yet been attempted for this reason. In order to initiate the development of a compression ignition engine operated under a neat hydrogen-air pre-mixture and room temperature conditions, this paper evaluates the feasibility of compression ignition by using a high compression ratio and analyzes the characteristics such as abnormal combustion and operation region. It is found that the neat hydrogen-air pre-mixture is self-ignited at a high compression ratio without any assisting method in room temperature, thus refuting the preconception that compression ignition of hydrogen engine is impossible. A compression ratio of at least around ε = 32 is required to self-ignite the engine under cold start and decreases to ε = 26 with an increased equivalence ratio under firing conditions. The minimum equivalence ratio for compression ignition is in the region of φ = 0.11-0.22 of an ultra lean mixture for all operating conditions. The operation region at each compression ratio is extremely narrow (around φ = 0.04-0.06) due to knocking and backfire resulting from the high compression ratio.

DRASTIC IMPROVEMENT OF THERMAL EFFICIENCY BY RAPID PISTON-MOVEMENT NEAR TDC

Y. MORIYOSHI,M. SANO,K. MORIKAWA,M. KANEKO 한국자동차공학회 2006 International journal of automotive technology Vol.7 No.3

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve high thermal efficiency, comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism were studied to avoid knocking with high compression ratio. Because reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to large heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adapted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving high thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in numerical simulations. Livengood-Wu integral, which is widely used to judge knocking occurrence, was calculated to verify the effect for the new concept. As a result, this concept can be operated at compression ratio of fourteen using a regular gasoline. A new single cylinder engine with compression ratio of twelve and TGV (Tumble Generation Valve) to enhance the turbulence and combustion speed was designed and built for proving its performance. The test results verified the predictions. Thermal efficiency was improve over 10% with compression ratio of twelve compared to an original engine with compression ratio of ten when strong turbulence was generated using TGV, leading to a fast combustion speed and reduced heat loss.

DRASTIC IMPROVEMENT OF THERMAL EFFICIENCY BY RAPID PISTON-MOVEMENT NEAR TDC

Moriyoshi, Y.,Sano, M.,Morikawa, K.,Kaneko, M. The Korean Society of Automotive Engineers 2006 International journal of automotive technology Vol.7 No.3

A new combustion method of high compression ratio SI engine was studied and proposed in order to achieve high thermal efficiency, comparable to that of CI engine. Compression ratio of SI engine is generally restricted by the knocking phenomena. A combustion chamber profile and a cranking mechanism were studied to avoid knocking with high compression ratio. Because reducing the end-gas temperature will suppress knocking, a combustion chamber was considered to have a wide surface at the end-gas region. However, wide surface will lead to large heat loss, which may cancel the gain of higher compression ratio operation. Thereby, a special cranking mechanism was adapted which allowed the piston to move rapidly near TDC. Numerical simulations were performed to optimize the cranking mechanism for achieving high thermal efficiency. An elliptic gear system and a leaf-shape gear system were employed in numerical simulations. Livengood-Wu integral, which is widely used to judge knocking occurrence, was calculated to verify the effect for the new concept. As a result, this concept can be operated at compression ratio of fourteen using a regular gasoline. A new single cylinder engine with compression ratio of twelve and TGV(Tumble Generation Valve) to enhance the turbulence and combustion speed was designed and built for proving its performance. The test results verified the predictions. Thermal efficiency was improve over 10% with compression ratio of twelve compared to an original engine with compression ratio of ten when strong turbulence was generated using TGV, leading to a fast combustion speed and reduced heat loss.

냉시동시 압축착화 조건의 상관관계에 관한 수소 HCCI 기관의 실험적 연구

이광주,이종구,안병호,이종태 한국수소및신에너지학회 2012 한국수소 및 신에너지학회논문집 Vol.23 No.6

It was found that the pure hydrogen-air pre-mixture was self-ignited at a high compression ratio without any assisting method in room temperature, thus refuting the preconception that compression ignition of hydrogen engine was impossible. Therefore, in order to analyze the correlation of compression ignition condition at cold start with hydrogen HCCI engine clearly, the possibility of compression igniting compression ratio is investigated with the change of equivalence ratio and engine speed, experimentally. As the results, it is confirmed that the possibility of compression-igniting compression ratio at cold start was decreased by increasing equivalence ratio due to decreasing auto-ignition temperature. In addition, it is grasped that the possibility of compression-igniting compression ratio at cold start is decreased around 14.9% by increasing engine speed at same supply energy.

초고강도 콘크리트(130MPa)에 대한 실험적 연구

조춘환 한국건설안전학회 2023 한국건설안전학회 논문집 Vol.6 No.1

High-rise, large-scale, and diversification of buildings are possible, and the reduction of concrete cross-sections reduces the weight of the structure, thereby increasing or decreasing the height of the floor, securing a large number of floors at the same height, securing a large effective space, and reducing the amount of materials, rebar, and concrete used for designating the foundation floor. In terms of site construction and quality, a low water binder ratio can reduce the occurrence of dry shrinkage and minimize bleeding on the concrete surface. It has the advantage of securing self-fulfilling properties by improving fluidity by using high-performance sensitizers, making it easier to construct the site, and shortening the mold removal period by expressing early strength of concrete. In particular, with the rapid development of concrete-related construction technology in recent years, the application of ultra-high-strength concrete with a design standard strength of 100 MPa or higher is expanding in high-rise buildings. However, although high-rise buildings with more than 120 stories have recently been ordered or scheduled in Korea, the research results of developing ultra-high-strength concrete with more than 130 MPa class considering field applicability and testing and evaluating the actual applicability in the field are insufficient. In this study, in order to confirm the applicability of ultra-high-strength concrete in the field, a preliminary experiment for the member of a reduced simulation was conducted to find the optimal mixing ratio studied through various indoor basic experiments. After that, 130 MPa-class ultra-high-strength concrete was produced in a ready-mixed concrete factory in a mock member similar to the life size, and the flow characteristics, strength characteristics, and hydration heat of concrete were experimentally studied through on-site pump pressing. 건축물의 초고층화, 대형화, 다양화가 가능하고 콘크리트 단면의 축소로 구조물 자중이 경감되어 보와 슬래브 두께를 얇게 함으로 층 고를 증감하거나 같은 높이에서 많은 층수를 축조할 수 있고 넓은 유효공간이 확보되며, 기초 저면 지정에 사용된 자재 및 철근과 콘크 리트 양을 절감하는 효과를 기할 수 있다. 현장시공 및 품질측면에서는 낮은 물결합재비 배합으로 건조수축 발생 저감 효과와 콘크리트 표면의 블리딩 최소화 효과를 얻을 수 있으며, 고성능감수제 사용에 의한 유동성 증진으로 자체 충전성이 확보되어 현장시공이 용이해지 며, 콘크리트의 조기 강도 발현으로 거푸집 탈형 기간을 단축시킬 수 있는 장점이 있다. 특히 근래에 들어 콘크리트와 관련한 건축기술의 비약적인 발전에 따라 초고층 건축물에서는 설계기준강도 100MPa급 이상의 초고강도콘크리트의 적용이 확대되고 있다. 그러나 최근 국내 에서도 120층 이상의 초고층 건축물들이 발주 또는 발주 예정되어 있으나, 현장 적용성이 고려된 130MPa급 이상의 초고강도 콘크리트를 개발하여 현장에서 실제 적용 가능성 여부를 실험, 평가한 연구실적은 미흡하다. 본 연구에서는 초고강도콘크리트의 현장적용 가능성을 확인하기 위하여 여러 가지 방법의 실내기초 실험으로 연구되어진 최적의 배합비를 찾아서 축소모의부재 예비실험을 실시하였다. 그 후 실물크기와 유사한 모의부재에 130MPa급 초고강도콘크리트를 레미콘 공장에서 생산하여 현장 펌프압송 타설을 통해 콘크리트의 유동특 성, 강도특성, 수화열에 관하여 실험 연구하였다.

고강도 후크형 강섬유로 보강된 콘크리트의 압축 및 휨 성능

왕기 ( Qi-wang ),김동휘 ( Dong-hwi Kim ),윤현도 ( Hyun-do Yun ),장석준 ( Seok-joon Jang ),김선우 ( Sun-woo Kim ) 한국구조물진단유지관리공학회 2021 한국구조물진단유지관리공학회 논문집 Vol.25 No.6

이 논문은 고강도 후크형 강섬유 보강량과 형상비에 따른 콘크리트의 압축 및 휨 성능에 미치는 영향에 대하여 다룬다. 이를 위하여 총 10개 콘크리트 배합이 계획되었다. 설계기준강도 30 MPa인 콘크리트에 형상비(l/d)가 64, 67, 80인 강섬유를 0.25%, 0.50%, 0.75% 혼입하여 강섬유 보강콘크리트가 제조되었다. 형상비 64, 67, 80인 강섬유의 인장강도는 각각 2,000, 2,400, 2,100 MPa이다. 시험 결과로부터 고강도 후 크형 강섬유의 혼입량은 콘크리트의 압축 및 휨 성능에 영향을 미치는 것으로 나타났다. 강섬유 혼입량이 증가함에 따라 푸아송비 및 압축인성은 향상되었으나 콘크리트의 압축강도 및 탄성계수에 큰 변화를 보이지 않았다. 강섬유 보강 콘크리트의 균열발생후 휨거동의 특성을 나타내는 잔여 휨강도 및 노치에서 시작된 균열면에서 에너지 소산능력은 강섬유의 혼입률 및 형상비에 따라 크게 좌우되었다. 특히 MC2010에서 정의된 사용 및 극한 상태한계에서의 잔여 휨강도는 강섬유 혼입량과 형상비가 증가함에 따라 증가되었다. This paper investigates the effect of high strength hooked-end steel fiber content and aspect ratio on the compressive and flexural performance of concrete. A total of ten mixtures were prepared and tested. Concretes with specific compressive strength of 30 MPa were reinforced with three different aspect ratios (l/d) of steel fibers 64, 67, and 80 and three different percentages of steel fibers 0.25, 0.50, and 0.75% by volume of concrete. Tensile strengths of steel fibers with l/d of 64, 67, and 80 are 2,000, 2,400, and 2,100 MPa, respectively. The compressive and flexural properties of plain and steel fiber-reinforced concrete (SFRC) mixtures were evaluated and compared. The experimental results indicated that the incorporation of high-strength hooked-end steel fibers had significant effects on the compressive and flexural performance of concrete. With the increase of steel fiber content, compressive performances, such as Poisson's ratio and toughness, of concrete were improved. The steel fibers with the least l/d of 67 resulted in a larger enhancement of compressive performances. The residual flexural strength, that is, post-cracking flexural resistance and toughness, of concrete is mainly depended on the dosage and aspect ratio of steel fibers. The residual flexural strength at serviceability (SLS) and ultimate limit state (ULS) defined in fib Model Code 2010 (MC2010) is increased as the fiber content and aspect ratio increase.

Numerical and Experimental Study on Knock Sources in Spark Ignition Engine with Electromagnetic Valve Train

Xu Jiangtao,Feng Yong,Chang Siqin,Guo Tongjun 한국자동차공학회 2020 International journal of automotive technology Vol.21 No.6

As one of the most common engine types in nowadays, the thermal efficiency of spark-Ignition (SI) engine is limited due to the lower compression ratio. Various technical solutions have been proposed to suppress knock and improve compression ratio of SI engines. In this paper, an new technical solution based on electromagnetic valve train (EMVT) was proposed to suppress knock of spark ignition engines, so that high compression ratio (HCR) engine (13:5) was obtained. Moreover, experimental and numerical analyses were carried out to optimize the proposed EMVT strategy. The result showed that the proposed EMVT strategies could well suppress the engine knock by reducing end-gas temperature and pressure and improving the spark-flame rate, resulting in significantly enhanced power, economic, and emission characteristics of SI engines. This study provides theoretical basis and technical approach for the development of internal combustion engines with high efficiency and high compression ratio.

고압축비 전기점화 엔진에서 저발열량 합성가스 연료의 연소 및 배기 특성

이준순(Junsun Lee),박현욱(Hyunwook Park),잠스랑 나랑후(Narankhuu Jamsran),오승묵(Seungmook Oh),김창업(Changup Kim),이용규(Yonggyu Lee),강건용(Kernyong Kang) 한국자동차공학회 2022 한국 자동차공학회논문집 Vol.30 No.4

Syngas with a high-octane number can be used as fuel for spark ignition engines with a high compression ratio to improve thermal efficiency. Furthermore, the use of syngas is advantageous in terms of lean combustion due to its low ignition energy, and improvement in thermal efficiency can be expected. The simulated syngas was composed of hydrogen(H₂), carbon monoxide(CO), and carbon dioxide(CO₂). In this study, the characteristics of combustion and exhaust emissions based on the composition of syngas and load conditions were investigated. The in-line, six-cylinder compression ignition engine, with a compression ratio of 17.1, was modified to become a single-cylinder spark ignition engine. The coefficient of the variation of indicated mean effective pressure(COV<SUB>IMEP</SUB>) was limited within 5 % at 1800 rpm for full and part load conditions. The maximum load was obtained under a stoichiometric air-fuel ratio(AFR) condition, while high efficiency could be achieved at the lean operating condition. The maximum load increased with a higher H₂ and CO composition of syngas. Moreover, the lean operating condition was expanded, and the highest efficiency operating condition was moved to a relatively leaner operating region. In the case of 15 % H₂, 15 % CO, and 70 % CO₂, stable engine operation was ensured under full and part load conditions with low calorific value syngas. However, the lean operation region was reduced, and there was a deterioration in the engine’s gross indicated thermal efficiency(ITE<SUB>g</SUB>).

Effects of train nose and blockage ratio on the formation process of the entry compression wave in a high-speed railway tunnel

Rohit Sankaran Iyer,Dong Hyeon Kim(김동현),Tae Ho Kim(김태호),Heuy Dong Kim(김희동) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

Entry compression wave is generated in a high-speed railway tunnel due to the train nose ingression at a very high velocity. Due to piston effect there is a sudden rise in pressure inside the tunnel which leads to the formation of the very first or the initial of the successive waves. Ulteriorly, this upsurges into a multitude of wave phenomena due to the reflection and collision of waves on the tunnel wall, thereby, creating a complex sequence of compression waves. Study undertaken here is about the formation process of entry compression wave as a high-speed train enters. A computational investigation on the effect of train nose and blockage ratio has been conducted using dynamic mesh technique. The train is moved using a CG_Motion UDF and the stationary mesh is updated using remeshing and smoothing techniques. The formation process of the entry compression wave has been studied in detail using multiple pressure monitors set on the tunnel wall and the results are comprehended using the pressure plots and contours obtained post the simulations. The post processed contour and vector images gives us a detailed insight on to the flow physics inside the tunnel with the change in above said parameters.

The Influence of Axial Compression Ratio on Seismic Behavior of SRUHSC Frame under Cyclic Loading

Dali Yao,Yingchao Ma,Jinqing Jia 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2

In this paper, the seismic behavior of Steel Reinforced Ultra-High Strength Concrete (SRUHSC) frames is experimentally studied under cyclic loading. Three one story-one span frames are carried out, and the main parameter is axial compression ratio. The major purpose is to investigate the seismic behavior of frames with the increasing of axial compression ratio, meanwhile, analysis the hysteresis curve, skeleton curve, stiffness degradation, energy dissipation and residual displacements. The test results reveal that the seismic response of the frame is closely related to the failure process and failure mode of the columns, which indicates that as the axial compression ratio increases, the failure process of the entire structure and the weakening of the beam end are accelerated. Meanwhile, a change of the failure mode is also observed, accompanied by corresponding changes in the strength, stiffness andenergy dissipation capacity, and the seismic behavior of frame structure decreases.