Effects of Varying Equivalence Ratios on the Combustion Efficiency Characteristic of a Dual-fuel Compression Ignition Engine by Changing Intake Pressures and Exhaust Gas Recirculation Rates

이정우,추상현,강재구,민경덕 한국자동차공학회 2024 International journal of automotive technology Vol.25 No.2

In general, a leaner mixture condition improves combustion effi ciency in compression ignition (CI) combustion using diesel. However, in the case of leaner air–fuel mixture conditions, it disturbs fl ame propagation in spark ignition combustionusing gasoline, i.e., low reactivity fuel, causing a decrease in combustion effi ciency. Since dual-fuel combustion in a CIengine typically involves the use of high- and low-reactivity fuels together, the diff ering reactivity conditions in the cylinderbecome as important as the local equivalence ratio in the cylinder. Thus, there is a need to verify the eff ect of a leaner mixturecondition on combustion effi ciency in dual-fuel CI combustion. For this reason, this study experimentally evaluates theeff ects of varying equivalence ratios on the combustion effi ciency of gasoline/diesel dual-fueled CI combustion in a 0.4-Lsingle-cylinder engine under low-speed (1500 rpm) and low-load (total LHV 570 J/str) conditions. To vary the equivalenceratios, intake pressures and exhaust gas recirculation (EGR) rates were, respectively, changed under the part-load condition. The results emphasize that as the equivalence ratio becomes leaner by increasing the intake pressure, combustion effi ciencyworsens due to the low reactivity properties and certain fl ame propagation modes of gasoline combustion. On the contrary,increasing the EGR rate did not signifi cantly infl uence combustion effi ciency, but it eff ectively helped reduce nitrogen oxide(NOx) emissions. Based on these results, it is concluded that optimizing dual-fuel CI combustion to suppress NOx emissionsis better achieved using EGR, rather than creating a leaner mixture condition.

Combustion characteristics of a methane engine with Air- and N₂-assisted direct injection

Song, Jingeun,Park, Sungwook Elsevier 2017 Fuel Vol.209 No.-

<P><B>Abstract</B></P> <P>Present study investigated effect of injecting assistance gases (air and N<SUB>2</SUB>) on the combustion characteristics of a single-cylinder methane spark ignition engine. Two gas injectors, namely direct injection (DI) and port fuel injection (PFI) injectors, were applied in this engine; the assistance gases were injected using the DI injector, and the methane was injected using the PFI injector. A one-dimensional simulation program, AMESim, was used to analyze the compositions of the in-cylinder gases. The assistance gas injection at 70 crank angle degree (CAD) before top dead center (BTDC) increased the combustion speed and the indicated mean effective pressure (IMEP) because the gas jet induced strong turbulent flow within the cylinder. Comparing the injection of air with the injection of N<SUB>2</SUB>, air injection yielded faster combustion even though the injection pressure and timing were the same. Simulation results showed that the combustion speeds of the air- and N<SUB>2</SUB>-assisted combustions were affected by the O<SUB>2</SUB> concentration. Because N<SUB>2</SUB> injection decreased the O<SUB>2</SUB> concentration whereas air injection increased it, the latter yielded faster combustion speed. The present work suggested three factors that increase IMEP: the fast combustion brought about by strong turbulence and high O<SUB>2</SUB> concentration, the high in-cylinder pressure brought about by assistance gas injection, and the high combustion efficiency brought about by lean combustion conditions. The air-assisted combustion conditions studied herein increased IMEP because the air injection during the compression stroke satisfied all of these factors. Air injection at 70 CAD BTDC increased the fuel conversion efficiency by about 3.5% compared to the normal combustion conditions without air injection. Thus, air-assisted combustion is an effective combustion strategy to increase engine efficiency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Air-assisted combustion yielded higher efficiency than N<SUB>2</SUB>-assisted combustion. </LI> <LI> 1D simulation code (AMESim) was used to analyze composition of in-cylinder gases. </LI> <LI> Combustion speed, O<SUB>2</SUB> concentration, and air–fuel ratio affected engine efficiency. </LI> <LI> Air-assisted combustion increased fuel conversion efficiency by about 3.5%. </LI> </UL> </P>

ANALYSIS OF VIBRATION ON AN ENGINE BLOCK CAUSED BY COMBUSTION IN A DIESEL ENGINE

Yoonwoo Lee,Seunghyun Lee,최회명,Kyoungdoug Min 한국자동차공학회 2019 International journal of automotive technology Vol.20 No.1

An accelerometer replaced an in-cylinder pressure sensor to detect the combustion status. The correlation between the vibration on an engine block caused by direct combustion as well as the combustion status was analyzed. The direct combustion vibration was determined. The direct combustion vibration on an engine block was blended with indirect combustion vibrations and other accessories. In addition, the combustion status was specified among several combustion status parameters, namely, RoHR, MPRR, and the peak pressure. There were two distinct vibrations in the motoring state. The frequency range of 2.5−8 kHz and 0−10oCA aTDC was assumed to be a crankshaft vibration. The other vibration, 1−3 kHz and 20−30oCA aTDC, was estimated as a slap motion of the piston. The combustion vibration frequency was 0.1−8 kHz after combustion. As an injector vibration (3−8 kHz) disrupted the search for combustion noise, a 0.1−2 kHz vibration range was appropriate for finding the correlation with the direct combustion state and the peak of the RoHR. As the peak of the RoHR was proportional to the combustion noise, the estimated peak of the RoHR can be used to control the diesel engine’s combustion noise. Estimation was possible in the transient and steady states.

가솔린 성층 연소의 분사 전략의 따른 화염 특성

박상재 ( Sangjae Park ),이상욱 ( Sanguk Lee ),배충식 ( Choongsik Bae ) 한국액체미립화학회 2018 한국액체미립화학회 학술강연회 논문집 Vol.2018 No.-

With high pressure gasoline direct injection, the Lean stratified combustion is a realizable solution to reduce loss in air exchange process of reciprocating internal combustion engine. However, due to the particle generation from the combustion process, the application of lean stratified combustion has been limited at commercialized vehicles. More gradient of stratification makes the combustion stable, but generates more locally rich mixture which could promote the soot generation. In other words, to accomplish stable combustion and low particle emission in stratified combustion, quite certain stratification between fuel cloud and surrounding air and well distributed fuel inside the cloud are required simultaneously. Therefore, in this study, by analyzing the spray and flame propagation of stratified combustion, the direction of injection strategies are suggested for cleaner gasoline stratified combustion. For the fuel injection process, an outwardly opening injector was applied to make hollow cone spray. The experiment was conducted under constant volume combustion chamber with elevated ambient pressure and temperature conditions. Higher ambient pressure make the atomization of spray enhanced, but the total area of spray was contracted. In addition, with higher temperature of surrounding air, the larger recirculation zones at inner and outer side of hollow cone, at relative upstream than lower case. The faster atomization and momentum dissipation was surly better to generate more homogeneous mixture. However, by overlapping of inner side recirculation zone, highly rich mixture was generated with elevated ambient temperature and pressure conditions. The locally rich mixture was observed as luminous flame in combustion process, with stationary position inside the hollow cone. On the other hand, low ambient pressure and temperature make the spray area larger, with retained momentum of spray. So that, the recirculation zone was smaller and more consistent than that of elevated temperature and pressure conditions. In combustion process, this consistent vortex generated locally rich mixture, and the larger area make the gradient of fuel ratio higher. As results of those, highly luminous flame was generated in the lower pressure and temperature condition, accompanying faster quenching of flame propagation. By summarizing these results, elevated pressure and temperature of surrounding air was better to reduce combustion loss and particle emission, but the overlapping of recirculation zone should be reduced to avoid the highly rich area inside the hollow cone. For engine application, more retarded injection would be better to reduce particulate emission and loss from combustion process.

Classification of diesel and gasoline dual-fuel combustion modes by the analysis of heat release rate shapes in a compression ignition engine

Lee, Jeongwoo,Chu, Sanghyun,Min, Kyoungdoug,Kim, Minjae,Jung, Hyunsung,Kim, Hyounghyoun,Chi, Yohan Elsevier 2017 Fuel Vol.209 No.-

<P><B>Abstract</B></P> <P>Reactivity controlled compression ignition (RCCI) is one of representative dual-fuel combustion concepts for low NOx, soot emissions and high thermal efficiency. Overall lean and highly premixed auto-ignition combustion make low combustion temperature and the reduction of heat transfer loss. Although premixed compression ignition (PCI) combustion using a single fuel, i.e., diesel, also shows low emissions and higher thermal efficiency, combustion characteristics of RCCI (dual-fuel PCI) are different from single-fuel PCI due to reactivity gradient from two different fuel characteristics as well as local equivalence ratio due to the fuel distribution. Therefore, it is necessary to know the influence of above two factors on the dual-fuel combustion characteristics for better understanding of dual-fuel combustion and its effective utilization. In this research, the characteristics of dual-fuel combustion are evaluated comparing to single-fuel combustion. Also, dual-fuel combustion modes are classified according to the analysis of heat release rate (HRR) shapes. Major factors in the classification of dual-fuel combustion modes are the degree of fuel reactivity gradient and the local equivalence ratio in the cylinder. Thus, the diesel injection timing, diesel and port injected gasoline fuel ratios and the overall equivalence ratio were selected as the main variables to characterize each dual-fuel combustion mode. The result emphasizes that the dual-fuel combustion could be classified as three types by HRR shapes, and it was mainly affected by reactivity gradient and overall equivalence ratio.</P>

Bioethanol and gasoline premixing effect on combustion and emission characteristics in biodiesel dual-fuel combustion engine

Park, S.H.,Yoon, S.H.,Lee, C.S. Applied Science Publishers 2014 APPLIED ENERGY Vol.135 No.-

The purpose of this study is to examine the effects of bioethanol and gasoline as a premixed injection source on the combustion performance and exhaust emissions characteristics of a dual-fuel combustion engine. The ignition source of dual-fuel combustion was biodiesel derived from soybean oil. The premixing ratio was calculated based on the total input energy and was varied from 0.2 through 0.8. Experiments were conducted using a single cylinder diesel engine with a re-entrant geometry type combustion chamber. Experimental results show that dual-fuel combustion has a higher maximum combustion pressure (P<SUB>max</SUB>), shorter ignition delay, significantly lower NO<SUB>x</SUB> and soot emission, but it has higher HC and CO emission when compared to single-fuel combustion. In a comparison of bioethanol and gasoline during dual-fuel combustion, biodiesel-bioethanol dual-fuel combustion showed lower P<SUB>max</SUB>, longer ignition delay, and higher IMEP than biodiesel-gasoline dual-fuel combustion. The increase in the premixing ratio for both dual-fuel combustion modes increased the ignition delay and IMEP, and decreased P<SUB>max</SUB>. With the increase in the premixing ratio, fuel consumption increased during biodiesel-gasoline dual-fuel combustion, but decreased during biodiesel-bioethanol dual-fuel combustion. NO<SUB>x</SUB> significantly decreased during biodiesel-bioethanol dual-fuel combustion; however, biodiesel-gasoline dual-fuel combustion had a limited effect on NO<SUB>x</SUB> reduction. HC and CO emissions were increased by bioethanol or gasoline premixing. The biodiesel-bioethanol dual-fuel combustion mode showed higher HC emission than the biodiesel-gasoline dual-fuel combustion mode, and the CO emission level was similar in both combustion modes.

Effect of air-fuel mixing quality on characteristics of conventional and low temperature diesel combustion

Han, S.,Kim, J.,Bae, C. Applied Science Publishers 2014 APPLIED ENERGY Vol.119 No.-

A comparative study on the effects of air-fuel mixing quality on combustion characteristics was carried out in both conventional and low temperature diesel combustion (LTC) regimes. The injection pressure and intake pressure were considered as variables as they are important factors which influence the air-fuel mixing process. The intake O<SUB>2</SUB> concentration was varied to realize different combustion regimes. Improved air-fuel mixing with a higher injection pressure enhanced the combustion process in both conventional combustion and LTC regimes, resulting in higher peaks of in-cylinder pressure and heat release rate. The combustion phase in the LTC regime was more influenced by injection pressure due to longer premixing time than that of conventional combustion. A higher injection pressure reduced CO and HC emissions over a wide range of intake O<SUB>2</SUB> concentrations. The reduction of CO and HC emissions in the conventional combustion regime was due to higher combustion temperature, while that in the LTC regime was due to decreased under-mixed fuel by improved air-fuel mixing. Soot emissions at a higher injection pressure were reduced, particularly, in the conventional combustion regime where the soot formation rate is high. The increase of intake pressure was also advantageous in reducing CO, HC and soot emissions due to improved air-fuel mixing as well as enrichment of absolute amount of oxygen, which lead to enhanced combustion process. A direct flame image was taken to observe the flame structure of two different combustion regimes to correlate with the exhaust emission results and combustion characteristics. High flame luminosity was observed around the periphery of the spray jet in the conventional combustion regime, which was a direct indication of soot formation and high temperature combustion; while low luminosity was observed around the piston bowl in the swirl direction in the LTC regime, which indicated a longer air-fuel mixing period and low temperature combustion.

야적 폐기물의 자연발화 기작 및 관리방안(I)

박진규 ( Jin-kyu Park ),김란희 ( Ran-hui Kim ),정민정 ( Min-jung Jung ),송상훈 ( Sang-hoon Song ),윤수철 ( Su-chul Yoon ),전덕우 ( Duk-woo Jun ),이남훈 ( Nam-hoon Lee ) 한국폐기물자원순환학회 2019 한국폐기물자원순환학회지 Vol.36 No.4

Spontaneous ignition of waste piles has been and continues to be a challenge in waste treatment. Spontaneous ignitions can pose a great threat to the safety of the surrounding environment and to human health. Thus, understanding the parameters that control spontaneous ignition is necessary to help predict and potentially mitigate these hazards. The objective of this study was to identify the mechanism of spontaneous ignition in waste piles. Two types of combustion can develop in waste piles: surface combustion, which is generally an occurrence of flaming combustion, and subsurface fires, which are generally occurrences of smoldering combustion. Smoldering combustion is a slow, low temperature, flameless form of combustion, and is self-sustained. Smoldering combustion can be continuously produced and it can change to flaming combustion if the air supply is not eliminated. Smoldering combustion also releases significant quantities of pollutants such as carbon monoxide. In order to extinguish these combustions effectively and cheaply, more parameters of the waste pile should be obtained, such as the temperature field and gas composition. Drilling holes at suspicious waste pile combustion areas can confirm whether these places are high-temperature areas or not. A carbon monoxide concentration of 1,000 ppmv can be utilized as an indicator of smoldering combustion. In addition, water in an amount ranging between 6.22 and 11.66 kg will be required at 25℃ to extinguish the heat produced by the flaming combustion of 1 kg of waste.

INFLUENCE OF INJECTION PARAMETERS ON THE TRANSITION FROM PCCI COMBUSTION TO DIFFUSION COMBUSTION IN A SMALL-BORE HSDI DIESEL ENGINE

T. FANG,R. E. COVERDILL,C.-F. F. LEE,R. A. WHITE 한국자동차공학회 2009 International journal of automotive technology Vol.10 No.3

In this paper, the influence of injection parameters on the transition from Premixed Charge Combustion Ignition (PCCI) combustion to conventional diesel combustion was investigated in an optically accessible High-Speed Direct-Injection (HSDI) diesel engine using multiple injection strategies. The heat release characteristics were analyzed using incylinder pressure for different operating conditions. The whole cycle combustion process was visualized with a high-speed video camera by simultaneously capturing the natural flame luminosity from both the bottom of the optical piston and the side window, showing the three dimensional combustion structure within the combustion chamber. Eight operating conditions were selected to address the influences of injection pressure, injection timing, and fuel quantity of the first injection on the development of second injection combustion. For some cases with early first injection timing and a small fuel quantity, no liquid fuel is found when luminous flame points appear, which shows that premixed combustion occurs for these cases. However, with the increase of first injection fuel quantity and retardation of the first injection timing, the combustion mode transitions from PCCI combustion to diffusion flame combustion, with liquid fuel being injected into the hot flame. The observed combustion phenomena are mainly determined by the ambient temperature and pressure at the start of the second injection event. The start-of-injection ambient conditions are greatly influenced by the first injection timing, fuel quantity, and injection pressure. Small fuel quantity and early injection timing of the first injection event and high injection pressure are preferable for low sooting combustion. In this paper, the influence of injection parameters on the transition from Premixed Charge Combustion Ignition (PCCI) combustion to conventional diesel combustion was investigated in an optically accessible High-Speed Direct-Injection (HSDI) diesel engine using multiple injection strategies. The heat release characteristics were analyzed using incylinder pressure for different operating conditions. The whole cycle combustion process was visualized with a high-speed video camera by simultaneously capturing the natural flame luminosity from both the bottom of the optical piston and the side window, showing the three dimensional combustion structure within the combustion chamber. Eight operating conditions were selected to address the influences of injection pressure, injection timing, and fuel quantity of the first injection on the development of second injection combustion. For some cases with early first injection timing and a small fuel quantity, no liquid fuel is found when luminous flame points appear, which shows that premixed combustion occurs for these cases. However, with the increase of first injection fuel quantity and retardation of the first injection timing, the combustion mode transitions from PCCI combustion to diffusion flame combustion, with liquid fuel being injected into the hot flame. The observed combustion phenomena are mainly determined by the ambient temperature and pressure at the start of the second injection event. The start-of-injection ambient conditions are greatly influenced by the first injection timing, fuel quantity, and injection pressure. Small fuel quantity and early injection timing of the first injection event and high injection pressure are preferable for low sooting combustion.

바이오매스와 폐기물 고형연료의 연소특성

구재회 ( Jae Hoi Gu ),오세천 ( Sea Cheon Oh ) 한국공업화학회 2012 공업화학 Vol.23 No.5

본 연구에서는 바이오매스의 에너지 활용성을 확인하기 위하여 실험실 연소로를 이용한 등온 및 비등온 연소특성 연구를 수행하였으며 바이오매스의 시료로는 목재펠렛, 볏짚 및 왕겨를 사용하였다. 바이오매스의 연소시 배출가스의 특성과 분진 및 잔류물을 분석하였으며 그 결과를 RDF의 연소실험 결과와 비교분석 하였다. 등온 연소특성 실험으로부터 볏짚이 다른 시료에 비하여 연소속도가 빨라 급격히 산소량이 감소되어 불완전연소율이 증가함을 확인하였으며 목재펠렛의 경우 다른 시료에 비하여 가장 낮은 NOx 배출농도를 나타내었다. 또한 비등온 연소특성 실험으로부터 모든 시료가 900 ℃의 연소온도에 도달하기 이전에 연소가 대부분 일어남을 확인할 수 있었으며 NOx의 경우 CO가 배출되는 범위와 유사한 온도범위에서 배출되는 반면에 SO2의 경우보다 고온에서 배출됨을 확인할 수 있었다. To verify the utilization of biomass as energy, the combustion characteristic has been studied by an experimental combustion furnace under an isothermal and non-isothermal combustion. The wood pellet, rice straw and rice husk were used as biomass samples in this work. The characteristics of emission gases, dusts and residues from biomass combustion have been analyzed and compared with those of reuse derived fuel (RDF). From isothermal combustion experiments, it was found that the incomplete combustion of rice straw was greater that that of rice husk, wood pellet and RDF. This is due to the fact that the combustion reaction rate of the rice straw was faster than that of other samples, and the oxygen concentration in rice straw combustion was rapidly decreasing. It was also found that NOx concentration of emission gas from wood pellet combustion was the lowest. From non-isothermal combustion experiments, it was found that all samples were burned before 900 ℃, Also, the temperature range of NOx emission was similar to that of CO emission, on the other hand, SO2 was emitted at a higher temperature than that of CO emission.