Study on ignition and combustion of gas jet and liquid spray fuels

Study on Ignition and Combustion of Gas-Jet and Liquid-Spray Fuels September 2009 Nguyen Ngoc Dung Content CHAPTER INTRODUCTION 1.1 Background introduction 1.2 Alternative fuels 1.2.1 Hydrogen 1.2.2 Natural gas 1.2.3 Biodiesel fuel 1.2.4 Gas-to-liquid fuel 10 1.3 Objectives and approaches 11 1.4 The structure of this thesis 13 References 13 CHAPTER METHODOLOGY FOR THE RESEARCH OF IGNITION AND COMBUSTION BY CONSTANT-VOLUME VESSEL UNDER DIESEL-ENGINE CONDITIONS 18 2.1 Introduction 18 2.2 Experimental setup and procedure 2.3.1 Constant-volume combustion vessel 2.3.2 Optical diagnostics 2.3.3 Experimental procedure 18 18 20 21 2.3 Determination of ignition delay 2.3.1 Ignition delay for gaseous fuel jets 2.3.2 Ignition delay for liquid fuel sprays 23 23 24 2.4 Combustion analysis 25 2.5 Experimental conditions 27 2.6 Conclusion 28 References 28 i CHAPTER SPONTANEOUS IGNITION AND COMBUSTION OF GASEOUS FUEL JETS UNDER DIESEL COMBUSTION CONDITIONS 30 3.1 Introduction 30 3.2 Experimental 33 3.3 Results and discussion 3.3.1 Penetration of hydrogen and natural gas jets 3.3.2 Effects of temperature 3.3.3 Effects of nozzle-hole diameter 3.3.4 Effects of injection pressure 3.3.5 Effects of ambient pressure 3.3.6 Effects of oxygen mole fraction 33 34 35 40 43 46 48 3.4 Conclusion 51 References 52 CHAPTER FUNDAMENTAL STUDY ON IGNITION AND COMBUSTION OF BIODIESEL FUEL FROM WASTE COOKING OIL 55 4.1 Introduction 55 4.2 Experimental 57 4.3 Results and discussion 4.3.1 Development of biodiesel fuel sprays 4.3.2 Effects of t emperature at an ambient pressure of MPa 4.3.3 Effects of temperature at an ambient pressure of MPa 58 59 61 66 4.4 Conclusion 68 References 69 CHAPTER IGNITION AND COMBUSTION OF GAS-TO-LIQUID FUELS 72 5.1 Introduction 72 5.2 Experimental 74 ii 5.3 Two-stage ignition determination 76 5.4 Results and discussion 5.4.1 Spray penetration and flame development of GTL fuels at base condition 5.4.2 Effects of temperature at MPa 5.4.3 Effects of temperature at MPa 5.4.4 Effects of injection pressure 5.4.5 Effects of oxygen mole fraction 5.4.6 Effects of nozzle-hole diameter 77 78 80 86 91 97 105 5.5 Conclusion 107 References 109 CHAPTER CONCLUSIONS 113 6.1 Gaseous fuel jets 113 6.2 Biodiesel fuel from waste cooking oil 114 6.3 Gas-to-liquid fuels 115 6.4 Recommendation for future work 116 ACKNOWLEDGMENTS 117 LIST OF PUBLICATIONS 118 iii CHAPTER Introduction 1.1 Background introduction Crude oil, gas and coal, known as fossil fuels, have played a crucial role in the world economy and world energy market Currently, modern industrial economies rely critically on fossil fuels to supply energy for transportation and to produce electricity for industrial and household purposes [1] The growth in energy demand or the increase in fossil fuel consumption is stimulated by many factors; predominant among them are the world population growth, economic growth, and the industrialization of developing countries or the continuous industrialization in developed countries [2] The Energy Information Administration (EIA-2009) has projected that energy consumption will increase at an average 1.1 percent per annum The world marketed energy consumption is projected to grow 44 percent over the 2006 to 2030 period Total world energy use rises from 472 quadrillion Btu in 2006 to 552 quadrillion Btu in 2015 and then to 678 quadrillion Btu 2030, in which total energy demand in the non-Organization for Economic Cooperation and Development (non-OECD) countries increases by 73 percent, compared with an increase of 15 percent in the OECD countries In terms of global consumption, liquids are expected to remain the most important energy source World consumption of liquids and other petroleum is expected to grow from 85 million barrels per day in 2006 to 91 million barrels per day in 2015 and 107 million barrels per day in 2030 [3] Fossil fuels possess many useful properties such as high energy density, safety and ease of use compared to others energy sources These advantages have made fossil fuel popular during last century In 2006, burning fossil fuels satisfied about 86 percent of world energy consumption Unfortunately, fossil fuels are non-renewable, and the limited resources are currently being depleted Shafiee and Topal [1] have computed and derived depletion times for fossil fuels reserves, and report that crude oil, coal and natural gas are likely going to be depleted in 35, 107 and 37 years, respectively The burning of fossil fuels produces harmful pollutants, which are destroying the environment and harming people‘s life The most dangerous product is the emission of carbon dioxide (CO2) Carbon dioxide is one of the greenhouse gases that enhances radioactive forcing and contributes to global warming, causing the average surface temperature of the Earth to rise World carbon dioxide emissions are predicted to rise from 29 billion metric tons in 2006 to 33.1 billion metric ton in 2015 and 40.4 billion metric tons in 2030-an increase of 39 percent over this projection period, according to the IEA [3] In addition, about 700 million tons of carbon monoxide, 150 million tons of nitrogen oxides, 200 million tons of solid particles, and 200 million tons of sulphur dioxides are released annually in the atmosphere [4] The majority of these substances are produced by the transport sector In the last three decades, the world has been confronted with energy crises due to the decrease in fossil resources, with the increase in environment constraints, and with the increasing prices of oil Lowering of world CO2 emissions to reduce the risk of climate change requires a major restructuring of the energy system This situation brings as a consequence the search of alternatives and renewable fuels, which have to be not only sustainable, but also techno-economically competitive Gaseous fuels of hydrogen, natural gas and bio-fuels like ethanol, vegetable oil, biomass, biogas, synthetic fuels, biodiesel, etc are starting to be of high interest to the developed countries [4] Liquid oils from petroleum are the main energy source for internal combustion engines Recently, the reduction of nitrogen oxides (NOx) and particulate matter (PM) in the exhaust of diesel engines to meet the upcoming automobile emission regulations have become the main directives for engine manufactures For this purpose, engine makers have introduced various techniques such as new modes of combustion [5,6], the high-pressure common-rail injection system with electronic controlled [7-9], the exhaust gas recirculation system (EGR) [10,11] and the aftertreatment system [12,13] for modern diesel engines because they satisfy the increasingly more stringent emission regulations Additionally, in order to provide engine manufacturers with phenomenological models to guide their designs, many researchers have started to develop methods to investigate diesel combustion mechanisms with a focus on the processes that lead to the production of soot and nitrogen oxides As a result, a wide range of engine modifications have being developed and implemented to achieve higher engine fuel efficiency and larger emissions reductions In direct-injection (DI) diesel engines, combustion sequence starts from the injection of fuel toward the end of the compression stroke in a small volume of high-pressure, hightemperature gases at which point the injected fuel autoignites and combusts in the expansion stroke The combustion process is usually composed of a premixed combustion phase, followed by a diffusion-combustion phase During premixed combustion, the levels of mixing are high and the local air-fuel ratio of the mixture range from above 14.5:1, the stoichiometric value, to beyond the limit of flammability in the outer boundary of the spray [14,15] The efficiency of the combustion process is strongly dependent upon, firstly, the charge-air, its temperature, pressure, motion and contents, secondly, the combustible fuel, its type, injection, atomization, evaporation, and thirdly, their states and interaction, leading to the auto-ignition and combustion of the charge [14], [16] Equivalence ratio () is used to present a measure of the relative amount of fuel and air The fuel-air mixture is defined rich if  >1 and contrarily it is called lean if  < The fuel-air mixing process during combustion produces soot particles in the highly rich regions of each fuel spray, and a high temperature during premixed-combustion contributes to the formation of NOx emissions For liquid diesel fuels, the injection spray consists of a cold, liquid phase core surrounded by a mixture that contains fuel droplets and vaporized fuel In order to burn, injected fuel must be in a vapor state The injected fuel is immediately atomized, vaporized and mixed with hot air at the time just after injection A high injection pressure and small nozzle-hole size normally provide smaller fuel droplets and faster fuel evaporation In high-temperature and high-pressure environments, first autoignition of the fuel occurs in the regions where the fuel-air equivalence ratio is appropriate Ignition delay or the process of autoignition is the most important fundamental parameter in the control of the combustion process in compression-ignition engines Combined with spray evaporation, the spatial and temporal evolution of the autoignition process determine the duration of the ignition delay period, a key parameter for engine design [17] Generally, ignition delay is determined as the time (or crank angle) between the start of injection and the rapid increase of premixed combustion The start of injection is determined by detection through the needle-lifts sensor The start of combustion is more difficult to determine precisely The best method is to identify the change in slope of the heat-release rate graph, determined from cylinder pressure data Both physical delay and chemical delay take place during ignition delay period Physical delay is associated with atomization, vaporization, and mixing, while chemical delay or the induction period process depends on factors including temperature, pressure, fuel properties and oxygen mole fraction These processes are affected by engine design, operating variables and fuel characteristics If ignition delay is too short or there is no ignition delay, the injected fuel will burn at the injector and there will not be enough oxygen around the injector resulting in incomplete combustion with high HC and soot emissions If ignition delay is too long, the accumulated fuel available for simultaneous explosion is large and thus it is causes rapid combustion with high pressure and temperature, contributing to an increase NOx emissions [18] and combustion noise The ignition characteristics of a fuel are very important in determining diesel engine operating characteristics such as fuel conversion efficiency, smoothness of operation, misfire, smoke emission, noise and ease of starting because they affect ignition delay Cetane number is often used to rate the ignition quality of a given fuel relative to a reference fuel Cetane number depends on the chemical composition of a fuel Fuels containing higher n-paraffinic hydrocarbons often have a higher the cetane number, while fuels containing high iso-paraffins are known to usually have lower cetane numbers The low cetane number fuels have a long ignition delay which causes a very rapid burning rate once combustion occurs with a high rate of pressure rise, a high peak pressure and a characteristic sharp knocking sound For high cetane number fuels, ignition delay is often short and the ignition occurs during injection Heat release-rate is controlled by injection rate and fuel-air mixing, and results in smoother combustion and smoother engine operation [14,15,18] The autoignition of air/fuel mixtures can be modeled by a detailed kinetic mechanism as a sequence of elementary chemical reactions In the case of diesel fuel, however, the number of intermediate species and possible reactions is very large and becomes prohibitive in terms of computing resources required Halstead et al [19] have published a simplified model that regroups all possible species under a limited number of generic species and reactions Recently, the constant-volume combustion vessel has become popular facility for diesel engine research The data obtained in this facility is useful for model development and validation because of the well-defined boundary conditions and the wide range of conditions employed Naber et al [20] performed experiments on effects of gas density and vaporization on penetration and dispersion of diesel sprays Siebers [21] performed a study of liquid-phase penetration length in diesel sprays The visualization of diesel spray penetration, cool-flame, ignition, high-temperature combustion, and soot formation using high-speed imaging are presented by Pickett et al [22] The work described in this thesis presents the study of ignition delay and combustion characteristics for several alternative fuels by using the constant-volume combustion vessel Prior to the main discussion, the following part of this chapter presents a background for the alternative fuels in this study 1.2 Alternative fuels This part focuses on analyzing potential, prospects and combustion characteristics of several alternative diesel fuels The fuels described in this part include hydrogen (H2), natural gas (NG), biodiesel fuel (BDF) and gas-to-liquid (GTL) fuel 1.2.1 Hydrogen Hydrogen offers tremendous advantages as a clean energy carrier In the coming decades, hydrogen and fuel cells will assume a greater role in meeting the world‘s energy consumption needs Hydrogen, like electricity, is an energy carrier, and can be produced directly from all primary energy sources, enabling energy feedstock diversity for the transportation sector These alternative energy sources include wind, solar power, and biomass (plant material), which are all renewable fuel resources Hydrogen derived from renewable energy sources has the potential to provide an inexhaustible supply of energy to fuel our cars, homes and industry without generating pollution Recently, electricity produced from nuclear fission, or fusion, has also been mentioned with increasing frequency as a possible source of H2 production through electrolysis of water or thermo chemical cycles A major benefit of increased H2 usage for power generation and transportation is that all of these sources minimize our dependence on non-renewable fossil fuels and diversify our energy supply for utilization in end-use energy sectors Alternatively, H2 can be produced through coal gasification, or by ―steam reforming‖ of NG, both of which are non-renewable fossil fuels but are abundantly available throughout the world Combining the latter technologies with carbon capture and storage would provide a significant increase in sources of clean burning H2 while at the same time eliminating greenhouse gas emissions The literature on hydrogen fueled internal combustion engines is surprisingly extensive and papers have been published continuously from the 1930‘s up to the present [23] One of the most important features of hydrogen engine operation is that it is associated with less undesirable exhaust emissions than compared to engines operating on other fuels Hydrogen has very high flame propagation rates within the engine cylinder in comparison to other fuels [24] This permits stable lean mixture operation and control in hydrogenfueled engines The operation on lean mixtures, in combination with the fast heat-release rates near top dead center associated with the very rapid burning of hydrogen–air mixtures results in high-output efficiency values The wide flammability limits of hydrogen in air 5.4.6 Effects of nozzle-hole diameter Together with injection pressure, nozzle-hole diameter is one of the significant and fundamental parameters in designing a combustion system in direct-injection diesel engines At constant of pj, a smaller dN provides smaller fuel droplets Injected fuel with smaller droplet easily evaporates and mixes with air To study effects of dN on the ignition and the combustion for GTL fuel (GTL1), experiments were conducted at the base condition: pj = 80 MPa, pi = MPa, rO2 = 21%, Ti from 600 to 1200 K, and with the range of values for dN = 0.14, 0.18, 0.22 and 0.25mm Fuel quantity was controlled constant for different of dN by adjusting injection duration Figure 5-21 shows Arrhenius ignition delay for GTL1 and gas-oil with different dN values The observation result indicates that the two fuels exhibit similar ignition delay trends:  decreases as dN increases More specifically, the ignition-delay values did not significantly change with the various dN values of 0.18, 0.22 and 0.25 mm However, the ignition-delay values at dN = 0.14 mm are shorter than those of standard dN of 0.22mm The smaller fuel droplets make the injected fuel to easily evaporate and mix with the hot air in the combustion chamber, and thus the ignition-delay values of the tested fuels are shortened The ignition-delay values of GTL1 are shorter than those of gas-oil at the same conditions of dN and Ti Figure 5-22 shows the change in heat-release rate curves for GTL1 and gas-oil at Ti = 750 K with changing in dN As shown this figure, both fuels, with different values of dN, exhibit a correspondence of dq/dt The typical progress of dq/dt is observed for both fuels: premixed combustion occurs after ignition delay, and then diffusive combustion follows For GTL1, a larger dN related to a higher rate of injection and larger fuel droplets shows a higher dq/dt rate For the results of gas-oil, the highest peak dq/dt is observed with dN = 0.22 mm In addition, the observation results indicate that a smaller dN gives a lower level and smaller slope increase dq/dt In comparison between GTL1 and gas-oil, GTL1 exhibits a lower dq/dt at every condition of dN This obtained result suggests that the NOx emissions may possibly decrease when using a smaller dN 105 Figure 5-21 Effects of dN on  for GTL1 and gas-oil at pi = MPa 106 Figure 5-22 Effects of dN on dq/dt for GTL1 and gas-oil at pi = MPa 5.5 Conclusion Ignition delay and combustion characteristics of GTL fuels have been fundamentally studied in a constant-volume combustion vessel under direct-injection diesel combustion conditions The research was conducted in a large range of ambient temperature and ambient pressure, which related to wide engine operation range from cold-start to warm-up conditions The obtained results provided useful information of spray penetration, mixture formation, the ignition and the combustion for several synthetic GTL fuels with different distillation properties The results of neat GTL fuels, blend GTL fuel were also compared to those of standard gas-oil Based on the final result, the conclusions of this study can be summarized as follows: All tested fuels exhibit similar ignition delay trends The observation identified that ignition delay increases as temperature, pressure, oxygen mole fraction decrease At all test conditions, the neat GTL fuels exhibit much shorter ignition delay than the blend GTL fuel and standard gas-oil Shorter ignition delay of GTL fuels is cause by high cetane number and low T90 temperature 107 In comparison among GTL fuels, ignition delay trends of GTL2 and GTL3 show slightly different compared to those of GTL1 at different temperatures The change of ignition delay trend is caused by changing properties of GTL fuels such as distillation temperature, viscosity, cetane number GTL fuels promote the combustion at low temperature and pressure conditions This result implies that GTL engines may easily operate at cold-start conditions Injection pressures did not much affect the ignition and the combustion for synthetic fuels and standard gas-oil High injection pressure exhibited higher heat-release rate, longer sprays penetration, longer liquid dense phase and somewhat shorter combustion duration Oxygen mole-fraction caused substantial changes in ignition and the combustion for all the tested fuels A decrease in oxygen mole fraction caused an increase in ignition delay At the same ambient temperature and ambient pressure, the variation of oxygen mole fraction caused a larger change in ignition delay values for synthetic fuels than for BGTL and gas-oil Low oxygen mole fraction exhibited slower combustion rate with smaller slope increase and lower peak heat-release rate Two–stage combustion with cool flame effect is observed at the condition of ambient pressure MPa and oxygen mole fraction 10% The combustion results of synthetic fuels with varying oxygen mole fraction suggested that EGR system is suitable for application in diesel engines fueled by synthetic fuels to get further NOx reduction The engine fueled by GTL fuels may produce better fuel conversion efficiency at higher EGR ratio owing to high ignitability of the synthetic fuels Nozzle-hole diameter exhibits small effect to ignition delay and heat-release rate Shorter ignition delay and lower lever heat-release rate increase can be obtained by using smaller nozzle-hole diameter 10 The blended GTL fuel has a reasonable ignition delay compared to standard gas-oil and the neat GTL fuel under variation of injection pressures and oxygen mole-fractions 108 The use of BGTL fuel in conventional diesel could improve combustion efficiency, thus improve engine performance, and reduce exhaust gas emissions 11 GTL fuels are observed to give smoother combustion with lower initial peak of heatrelease rate and easily to combust at low entire temperatures This result suggests GTL fuels may produce higher combustion efficiency and much emissions reduction in coldstart operation condition in diesel engines Furthermore, this result also implies that GTL fuels may possibly suitable apply for low temperature combustion system in an attempt to reduce NOx and particulate emissions 12 Liquid phase of GTL spray is observed slightly shorter than gas-oil The shorter liquid phase suggests that GTL fuel is easy to evaporate and to mix with air, forming a more combustible charge during autoignition period A lower T90 temperature of GTL fuel suggests that it has less heavy distillation and easy to evaporate In comparison between GTL1 and GTL3, GTL3 spray is also observed with shorter liquid phase than GTL1 spray The reason can be explained by much lower T90 and much lower viscosity of GTL3 fuel compared to GTL1 13 At all test conditions, the synthetics fuel flames have lower light intensity compared to those of gas-oil The lower light intensity may possibly be considered as a measure of soot concentration References [1] L Shi, Y Cui, K Deng, H Peng, Y Chen, Study of low emission homogeneous charge compression ignition (HCCI) engine using combined internal and external exhaust gas recirculation (EGR), Energy 31 (2006) 2665-2676 [2] D 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Miyasato, A Oshinuga, G Barton, et al., Achievement of Low Emissions by Engine Modification to Utilize Gas-to-Liquid and Advanced Emission Controls on a Class Truck, The 2005 SAE Powertran & Fluid Systems Conference & Exhibition SAE Paper No 2005-01-3766 (2005) 111 [30] I Sakata, K Kitano, N Uchida, M Umemoto, A Imai, N Okabe, et al., Development of FTD Fueled Vehicle, JSAE Paper No 20085189 (2008) [31] L Xinling, H Zhen, Emission reduction potential of using gas-to-liquid and dimethyl ether fuels on a turbocharged diesel engine, Science of The Total Environment 407 (2009) 2234-2244 [32] Rosli Abu Bakar, A.R Ismail, Semin, Fuel Injection Pressure Effect on Performance of Direct Injection Diesel Engines Based on Experiment , American J of Applied Sciences (2008) 197-202 112 CHAPTER Conclusions Alternative fuels of hydrogen, natural gas, biodiesel fuel and gas-to-liquid fuel were fundamentally studied the ignition and the combustion by using constant-volume combustion vessel This chamber was able to simulate both current and anticipated incylinder conditions of automotive diesel engines, while at the same time allowing good optical access to the diesel spray The sprays (jets) penetration and flames development with time data were obtained from high-speed shadowgraph images The effects of fuel evaporation, breakup and air entrainment at the initial stage of spray penetration were studied practically Spray autoignition and combustion characteristics were investigated using high-speed shadowgraph image, in-cylinder pressure, and heat-release rate 6.1 Gaseous fuel jets Every gaseous fuel exhibited the similar ignition delay trend Ignition delay increases as an temperature decreases Among these fuels, hydrogen exhibited much shorter than NG and CH4 at the same of Ti, and could be ignited at a lower temperature, Ti = 780 K Shorter ignition delay of H2 could be attained by means of controlling the mixture formation with lowering injection pressure, enlarging nozzle-hole diameter, increasing ambient pressure and increasing oxygen mole-fraction In contrast, methane showed the longest  over the whole range of Ti and suffered from misfiring at a higher Ti of 910 K For natural gas, ignition delay indicated shorter than CH4 due to a small amount of C4H10 with good ignitability Ignition delay of NG exhibited slightly different when dN and pj vary but drastically changed when pi and rO2 decrease The main advantage of applying H2 and NG as a fuel for internal combustion engine is the potential to reduce engine emissions with NOx being the only major concern The compression-ignited version of hydrogen and natural gas engines require TDC temperatures 113 in excess of 900 K and 1100 K, respectively, to achieve a short ignition delay 1-2 ms The obtained results indicated that TDC temperature of hydrogen and NG gas could be reduced by increasing ambient pressure without increasing the ignition delay and combustion rate An increasing ambient pressure could be achieved by increasing engine compression ratio On the other hand, the results of this study indicated that it could be used lower oxygen mole fraction with not significantly increasing the ignition delay and reducing combustion rate at high temperature (hydrogen) In other word, the use of low oxygen mole fraction could increase TDC temperature An increase TDC temperature and a reduction in oxygen mole fraction could be attained through use of high-level in-cylinder EGR To obtain temperatures over 900 K at TDC, the trapped gas temperature at intake-valve closing would have to be increased by at least 11.25% over current diesel engines (900K /800 K = 1.125, where 800 K is a typical DI diesel engine with equivalence ratio around 16 at TDC temperatures) In conclusion, DI compression-ignition H2 engine may operate well at a high compression ratio (over 20) and high level in-cylinder EGR ratio At high compression ratio and high EGR ratio, enlarging nozzle-hole diameter and increasing injection pressure may possibly reduce ignition delay and TDC temperature However, the modified of dN and pj settings are greatly effects combustion rate In addition, high compression ratio is recommended to apply for DI compression-ignition NG engine The application of high EGR level can help improve TDC temperature, however, it slightly affects combustion rate 6.2 Biodiesel fuel from waste cooking oil Biodiesel is one of the most attractive renewable diesel fuels to resolve ongoing concerns about environmental issues and sustainable energy due to its carbon-neutral characteristic The experimental results show a great effect of temperature and pressure on the ignition and combustion processes for the tested BDF fuels from waste cooking oil It is shown that (i) the fresh BDF exhibits a longer ignition delay than the gas-oil, (ii) a small amount of isopropyl alcohol as an additive in BDF promotes the ignition, (iii) the oxidized BDF with acid value changed from 0.1 of the fresh one to 0.22 (KOHmg/g) shortens ignition delay 114 almost same as standard gas-oil, and (iv) the blend BDF with twenty percent in volume to gas-oil results in a reasonable ignition delay Additionally, the results at pressure MPa, which simulate condition of PCCI (premixed charge compression ignition) engine operations in future engine trends, present a two-stage ignition and low-temperature combustion characteristics for both BDF and gas-oil Ignition delay trend and combustion characteristics of biodiesel fuels from waste cooking oil and its blend are similar to those of standard gas-oil These obtained results imply that BDF can apply on diesel engine possibly without any problem However, the longer ignition delay of BDF at low temperature possibly causes difficult operation at cold start, especially at cold weather To solve this problem, the using of additive BDF may suitable because it promotes the ignition In addition, blend BDF fuel is suggested to apply for diesel engine because they can partially replace diesel fuel, reduce engine exhaust gas emissions, but not much affect the ignition and the combustion characteristics compare to standard gas-oil 6.3 Gas-to-liquid fuels Gas-to-liquid fuel exhibits potential as one of the most clean alternative diesel fuel Ignition delay trend of GTL fuels was observed significantly dependence on distillation characteristics Gas-to-liquid fuels with high cetane number exhibited much shorter  and smoother combustion process than that of gas-oil at the same temperature and pressure All tested GTL fuels generally exhibited the similar trend of ignition delay  and combustion characteristics with the variation of injection pressures and oxygen mole fractions The different pj did not significantly affect the ignition of the tested fuels; however, the results of heat-release rate result were observed increase for the higher pj Otherwise, the different oxygen mole-fractions exhibited a significant change in the ignition and the combustion Ignition delay increases as oxygen mole-fraction in combustion vessel decreases; and two-stage ignition with cool flame effects could be observed at ambient pressure MPa and oxygen mole-fraction 10 percent Blended GTL fuel exhibited a reasonable short ignition delay compared to standard gas-oil and the neat 115 GTL fuel under variation of injection pressures and oxygen mole-fractions In addition, the observation result recognized that synthetics GTL fuels have slightly shorter spray penetration length and lower light intensity flames compared to those of gas-oil Furthermore, the blend of GTL to gas-oil helped improve ignition quality and combustion efficiency of this fuel These obtained results may contribute for finding the optimal condition of design and operation in diesel engines fuelled by GTL fuels 6.4 Recommendation for future work The constant-volume combustion vessel in this research was specially designed to study the ignition and the combustion characteristics for various alternative fuels This research have been investigated fundamental data of hydrogen, natural gas, biodiesel fuel from waste cooking oil and several GTL fuel with different distillation properties The continuous works are suggested as follows: - Ignition-delay values of H2 jets are much scatter than NG at low temperatures The reasons may be caused by an injector leak It is suggested to perform more experiments at low temperatures by using high-speed camera - The variation of ignition-delay value for BDF fuels suggested that biodiesel produced from different sources possibly generate different ignition characteristics Biodiesel fuels from palm oil, jatropha curcas oil, soybean oil, rapeseed oil, and coconut oil are very popular The study of the ignition and the combustion for these fuels are suggested - Ignition delay and combustion characteristics of several alternative fuels have been performed in this research However, it is suggested to study formation of soot and NOx for these fuels because those emissions are major problem of diesel engine - Synthetic GTL fuel performed shorter ignition delay and smoother combustion than those of gas-oil Dimethyl ether (DME), another promising synthetic fuel to replace diesel fuel is also suggested for future investigation 116 Acknowledgments I would like to thank Graduate School of Energy Science, Kyoto University, who gave me the opportunity for doing my research I would like to express my sincerest gratitude to Prof Masahiro Shioji for his support, constant guidance, encouragement, and enthusiasm during the course of this study I would like to thank all staffs, Prof Takuji Ishiyama, Assoc Prof Hiroshi Kawanabe, technicians, assistants and students of Combustion and Power Engineering Laboratory for their supporting and helping throughout my studying time I am very grateful to Mr Morishima, Mr Fujita and Mr Ishida for their valuable time helping me in experiment Special thank to thank to Showa Shell Sekiyu K.K for supplying GTL fuels and to Department of Environment of Kyoto City for BDF fuels I would like to thank for Research Fellowships of AUN/SEED-Net, JICA I am deeply grateful to all JICA staffs at Osaka Branch, who always take care and support me during my studying time My grandmothers, parents, sisters, brothers, friends are always a constant source of endearment, support, and encouragement I should thank every one of them Above all, I thank Christ, the almighty, for his help, care, and protection Nguyen Ngoc Dung 117 List of publications Journal papers Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Study on Ignition Delay and Combustion Characteristics of Gaseous Fuel Jets, Journal of Engineering for Gas Turbines and Power, (2009) (In press) Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Ignition and Combustion Characteristics of FAME from Waste Edible Oil, Fuel (2009), (Accepted) Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Ignition and Combustion Characteristics of Gas-to-Liquid Fuel for Different Ambient Pressures, Energy&Fuels (2009), (Accepted) Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Gas-to-Liquid Sprays for Different Ambient and Injection Conditions, Journal of Engineering for Gas Turbines and Power, (2009), (Accepted) Conference papers Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Ignition and Combustion Characteristics of Gas-to-Liquid Diesel Fuels at Different Ambient Pressures, APAC15, Hanoi, Vietnam, 2009 (October) (Accepted) Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Ignition and Combustion Characteristics of FAME from Waste Edible Oil, The 1st Asian University Network/ Southeast Asia Engineering Education Development Network Regional Workshop on New and Renewable Energy, Bandung, Indonesia, pp 57-64, (2009) Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Ignition Delay and Combustion Characteristics of FAME from Waste Edible Oil, The International Workshop on Automotive Technology, Engine and Alternative Fuels, HCMUT, Vietnam, pp 32-37, (2008) 118 Nguyen Ngoc Dung, Hiroaki Ishida and Masahiro Shioji, Ignition and Combustion Characteristics of FAME from Edible Oil, The 5th International Conference on “Combustion, Incineration/Pyrolysis and Emission Control (i-CIPEC 2008)”, Chiang Mai, Thailand, CD-ROM, (2008) Nguyen Ngoc Dung, Akihito Fujita and Masahiro Shioji, Ignition and Combustion Characteristics of Alternative Diesel Fuels, The 7th JSME-KSME Thermal and Fluid Engineering Conference, Japan, CD-ROM (2008) Iman K R., Tirto P B., Tatang H S., Wiranto A., Nguyen N D, Rey S.,Tran Q T., Ogawa H., The Study of Combustion of Jatropha Curcas Linn.Oil (Crude; Degummed; Fatty Acid Methyl Ester) as a Fuel on a Direct Injection Diesel Engine (DI), The 7th Comodia, Japan, pp 787-792 (2008) Dung Ngoc Nguyen, Akihito Fujita and Masahiro Shioji, Ignition and Combustion Characteristics of Unsteady Hydrogen Jets, The 17th World Hydrogen Energy Conference, Australia, CD-ROM (2008) Akihito Fujita, Nguyen Ngoc Dung, Masahiro Shioji, Study on Ignition and Combustion Characteristics of Alternative Fuel Sprays, JSME Annual Congress, (2008) Nguyen Ngoc Dung, Tsuyoshi Morishima, Akihito Fujita, Sung-Sub Kee, Masahiro Shioji, Study on Ignition and Combustion Characteristics of Gaseous Fuel Jets, JSAE Annual Congress , (2007) 10 Tsuyoshi Morishima, Nguyen Ngoc Dung, Akihito Fujita, Sung-Sub Kee, Masahiro Shioji, Study on Ignition and Combustion Characteristics of Unsteady Gas Jets, JSME Annual Congress, (2007) 119 ... various gasjet and liquid- spray fuels under simulated diesel combustion conditions, in terms of:  Jets and sprays penetration and dispersion with time  Vapor phase penetration and mixture formation... results: ignition delay definition for gaseous fuel and ignition delay definition for liquid fuels 2.3.1 Ignition delay for gaseous fuel jets The definition of ignition delay these gaseous fuels. .. ignition was reported to be negligible [2], [10] 2.3 Determination of ignition delay Both liquid and gaseous fuels were fundamentally studied ignition and combustion Two definitions of ignition