| The agricultural and forestry wastes are rich in China,but they haven't been used effectively,causing environmental problems.The incomplete combustion of gasoline and diesel of motor vehicle also is an important source of PM 2.5.A large number of studies have shown that adding oxygenated liquid fuel could reduce PM2.5 emissions significantly.Contributed to the oxygen it contained,biomass is an ideal material for the production oxygenated liquid fuel.Biomass Fast pyrolysis technology could continuously convert biomass bio-oil efficiently.However,the problem that using bio-oil in internal combustion engines stably still exists,solving this problem could promote the production of biomass-based oxygenated liquid fuel with the processing of agriculture and forestry wastes.In this paper,to deal with the problem,with the idea of fuel design,the connection between the molecular structure and combustion reactivity of the bio-oil compounds has been analyzed firstly.Then to meet the requirement of diesel fuel,a high-oxygen-content and high-combustionactivity polyol ethers fuel has been directionally designed.The hydrogenation/etherification production pathways of hydrogenated bio-oil to polyol ethers has been verified.Furthermore,the spray and oxidation characteristics of polyol ethers under compression combustion conditions have been studied,and the key factors that influence the low-temperature kinetics has been found.Finally,the combustion and emission characteristics of polyol ethers in a small-scale diesel engine have been checked.The compression combustion activities of bio-oil main components under compression conditions has been tested by a CFR engine,based on the strongest to weakest combustion activity,the sequence was as follows: furan derivatives > polyols > aromatics > short-chain esters.It has been found that the position of oxygen and the length of molecule influenced the combustion activities mostly.The miscibility of polyols in diesel was poor,couldn't meet the demand of diesel engine.Finally,the combustion and emission behaviors of blending 10% vol.ethanediol in diesel was similar to 10% vol.ethanol and ethyl acetate blending,achieving the reduction of soot and CO emissions.However,it still needs further upgradation to add the carbon-chain length of the biooil components to get stable and efficient oxygenated diesel additives.Based on the results,the research idea that transfer the oxygen in the branched chain to the main chain has been proposed to increase the compression combustion activities of upgraded bio-oil.Based on the fuel design idea and the national standards of diesel,selected with parameters as spray characteristics,combustion behaviors,oxygen content,transportation safety,low-temperature flowability,polyol ethers fuel with cetane number > 60 and oxygen content between 25% ~ 40% has been chosen as the goal of hydrogenated bio-oil upgradation.Based on the results from fuel design,the reaction pathway from hydrogenated bio-oil model compound ethanediol to polyol ethers model compound TPGME has been put forward.It has been found that the reaction pathway was favored in alkane environment by quantum chemistry calculation.Under this condition,a series of zeolite catalysts with basic sites has been prepared and tested,showing that K-ZSM-5 catalyst had the best performance.The experimental results also revealed that propylene glycol had two different competition mechanism,basic sites and catalyst channel sites.The reaction pathways used the natural oxygen in biomass,could reduce the usage of biomass raw materials.To get 1 ton polyol ethers,only 6,9 ton biomass was needed.The spray and compression ignition characteristics of TPGME have been systematically investigated in a constant volume incendiary.The difference of spray cone angle between TPGME and diesel could be neglected,and the spray liquid length of TPGME was 20% shorter than diesel.Under constant volume combustion chamber and compression combustion conditions,the combustion activity of TPGME was better than diesel model compound n-heptane.The ignition delay time of TPGME was 6ms shorter than n-heptane at 540 oC.Blending 20% vol.polyols into TPGME would decrease the overall activity of TPGME,but it still kept the low temperature heat release phenomenon.The combustion process of TPGME was controlled by diffusion process and chemical kinetics process,while the combustion process of TPGME was controlled by diffusion process.13 kinds of intermediate products have been collected and analyzed,revealing that the low temperature combustion mechanism of TPGME showed similar reaction pathways as traditional hydrocarbon liquid fuels,but the involvement of oxygen atom also introduce new reaction pathways for TPGME.Based on the low temperature combustion mechanism of traditional hydrocarbon liquid fuel,two key factors involved in the low temperature combustion kinetics have been sorted out,one was the number of carbon that could load peroxyl radicals,another one was that once peroxyl radicals was loaded,the number of carbon that could support the hydrogen transfer reactions.With these two factors,the linkage between molecular structure and combustion activity has been established.Using the linkage,the phenomenon that the low temperature oxidation activity of TPGME was higher n-heptane and that why hydrogenated bio-oil model compounds don't have low temperature phenomena could be explained.Finally,the combustion and emission characteristics of TPGME in diesel engine has been checked systematically.When diesel was blended with TPGME,the in-cylinder pressure could be increased around 5%,the NO emission could be decreased around 10%,the effective fuel consumption could be increased around 20% ~ 100%,the CO emission could be decreased around 15%~40% based on the blending ratio of TPGME.Within normal power scope,nearly 100% soot reduction could be achieved.Under same blending ratio,the combustion and emission behaviors of blending TPGME was better than ethanol.By characterization methods,such as SEM?TEM?EDS?XPS,it has indicated that the introduction of oxygen in TPGME made the oxygen content in soot from TPGME was higher than diesel soot and decrease the graphitization degree of TPGME soot. |
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