| It is an effective measure to relieve the energy shortage condition and reduce the environmental pollution that the diesel engine fueled with oxygenated fuels. Polyoxymethylene Dimthyl Ethers(PODE) is a new coal-based fuel, which synthesis from methanol and dimethyl ether or other coal base methanol-ether fuels. The PODE have a broad future due to the higher cetane number and oxygen content.In this research, 5%, 10% and 15%(by volume) PODE with 3~8 polymerization degree were separately blended with diesel fuel, marked as P5, P10 and P15. The mutual solubility and stability of blended fuels were studied and physico-chemical properties had been analyzed.The volatility, oxidation characteristic and thermal parameter calculation of fuel samples with different PODE3~8 ratios were studied by using thermogravimetric analyzer under O2 atmosphere. Results showed that compared with diesel fuel, initial mass loss temperatures and initial combustion temperatures were decreased with the increasing PODE3~8 ratio. The thermal stability decreased and the composite combustion index increased with the increase of blending ratios. Additionally, the activation energies of P5, P10 and P15 fuels which was calculated by Coast-Redfern method were decreased.The combustion and emissions characteristics of the diesel engine with these four test fuels also had been investigated. At the rated condition, the ignition delay period shortened, the peak heat release rate in premixed combustion section decreased, the highest cylinder pressure and the peak heat release rate in diffusion combustion section increased as the blending ratio increased. As compared with diesel fuel, brake specific fuel consumptions of the three blended fuels were increased by 0.8%, 3.2% and 8.5%, but the effective thermal efficiency were increased 2.8%, 4.2% and 3.1%, respectively. CO emissions were decreased by 11.8%, 14.0% and 18.8%, HC emissions were decreased by 19.2%, 26.8% and 21.7%, and smoke emissions were decreased by 25.2%, 30.8% and 32.1%, while the NOx emissions had changed little when engine fueled with these three blended fuels.The micro-orifice uniform desposition impactor was used to study the size distribution characteristics of the exhaust particles of diesel engine. The mass fraction of soluble organic fraction(SOF) in PM and the characteristics of soot oxidation were analyzed with thermo-gravimetric analyzer(TGA), while the influence of PODE3~8 fuel on the SOF components of PM samples has also been analyzed with gas chromatography-mass spectrometer(GC-MS). The mass concentration of each particle size of P10 fuel has decreased when compared with diesel; The exhaust particle size distribution generally shifted to the direction of small particle size when the diesel engine fueled with P10 fuel, and the proportion of particle in accumulation mode in total exhaust particle have been increased slightly. As compared with diesel, the mass fractions of SOF in PM of P10 fuel increased by 7%, the initial combustion temperatures and the mass loss rate peak temperatures were reduced by 44℃ and 46℃. For P10 fuel the mass fractions of alkanes and polycyclic aromatic hydrocarbons(PAHs)(such as fluoranthene and pyrene) in SOF had been significantly reduced to 31.7% and 3.7%, but the organic acid esters had been increased to 45.5%. |
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