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The diesel particulate filter (DPF) with the trapping has become an effective and broadly used measure. However, the trapped particulates adhering to the carrier channel easily block the exhaust channel, and then consequently affect the power performance and fuel economy of the diesel engine. Catalytic technology can effectively reduce the temperature for soot combustion by coating the active catalytic material on the channel wall of DPF. The molybdenum catalyst shows excellent catalytic performance in many research fields. The high catalytic activity of molybdenum catalysts is mainly related to the mobility of the active species in the reaction condition, or by the surface migration or by the melting of molybdenum catalyst, so this mobility could improve the contact between reactants and catalyst. Thus, according to that idea, in a loose contact situation between soot and catalyst, the migration of the active component across the soot surface could play an important role in the oxidation reaction during trap regeneration. In order to thoroughly study the surface activity structure phase of the supported molybdenum catalyst and its' function mechanism on soot oxidation, nano-scale MoO3/TiO2 catalysts for soot oxidation were prepared by loading different amounts (5%, 10%, 20% and 40%) of MoO3 on the TiO2 particles through an impregnation method. The structures and physico-chemical properties for those catalysts were characterized using BET, Fourier transform infrared spectra (FT-IR), X-Ray diffraction (XRD) and a Scanning electron microscope (SEM). Printex-U carbon black has been often used in the research field of catalytic oxidation of diesel soot. The practical engine soot and Printex-U carbon black have more characteristics in common such as components and structures. Besides, the reproducibility of the test seemed satisfactory, too. Printex-U carbon black was chosen to replace the practical engine soot. The catalytic activity of molybdenum catalysts for soot oxidation was evaluated using a TG/DTA analyzer. Based on the Starink method, the catalytic oxidation process of soot was quantitatively analyzed. The results showed that, for the limitation of dispersion threshold value, the structure of active MoO3 was amorphous or micro crystalline at the low molybdenum loading. When the MoO3 loading rate was more than 10%, the significant MoO3 orthorhombic crystals appeared on the catalyst surface. The light sheet and octahedral crystal structure with close texture appeared in the MoO3 catalyst surface. The functional groups Mo=O were stable in all samples, and its content increased with the increase in molybdenum loading rate. Under a loose contact state, MoO3 characterized with low melting point, still showed good catalytic effect. With the increase in MoO3 loading rate, TG and DTG curve moved to the low temperature area, the characteristic temperatures of soot oxidation were decreased, and the catalytic activity of catalyst was increased. Conversely, the specific surface area and pore volume of the molybdenum catalyst were decreased. However, the catalytic activity was not limited by the specific surface area and threshold effect, and it was closely bound up with the content of the active component MoO3. Among all samples, the catalyst loaded by 40% MoO3 exhibited the highest catalytic activity for soot oxidation. The ignition temperature, the temperature of weight loss peak and the burnout temperature of soot oxidation were reduced about 84.4, 122.6 and 122.7? respectively, as compared with the non-catalyzed particulates. The order of the activation energy for soot oxidation worked out by the Starink method was soot < Mo:Ti (mass ratio 5:95) < Mo:Ti (mass ratio 10:90) < Mo:Ti (mass ratio 20:80) < Mo:Ti (mass ratio 40:60). Thereby, with the increase in the MoO3 loading rate, the catalytic activity of MoO3/TiO2 catalyst was increased. [ABSTRACT FROM AUTHOR]

In order to achieve the target of emission purification within the aspect of combustion optimizing in a cylinder, as well as the partial replacement of fossil fuels, a study on the combustion process of dimethyl carbonate (DMC)-diesel fuel blend was carried off. A fuel blend D10 (10% DMC and 90% diesel by volume) was chosen as the test fuel. The experiments were conducted on a single-cylinder research engine originated from a Daimler Benz OM646 2.2 litre common rail direct injection four-cylinder in-line diesel engine. As for the research engine, the indicated mean effective pressure pmi was adopted as the baseline for assessment of engine performance. A given load at 1900 r/min was chosen as the engine operating mode. According to the first law of thermodynamics, the heat release rate can be presented in real-time by the IndiCom software. The exact position in the crank angle of the center of heat release (COHR, 50% of the total heat release) can be figured out by interpolation. It was a key parameter to describe the combustion process of the engine. Through a fuel injection strategy characterized by an adjustable first pre-injection phase but constant phase intervals between the three injections and adjustable main injection duration but fixed durations of first pre-injection and second pre-injection, the accurate COHR target at a steady working mode can be implemented. Therefore five modes with an even interval of COHR, under the same engine speed and pmi, were inspected. As for D10 fuel, to compensate for its energy density falling, the rail pressure of D10 was 3 MPa higher than that of a diesel. While using D10 fuel, two schemes were considered. One was to keep the injection parameters of fuel system unchanged. The other was to slightly adjust the injection parameters, thus the COHR can be precisely accorded with the original diesel engine. When multiple injection strategy was adjusted to achieve the exact COHR which was delayed in constant step, the features of the combustion process of a diesel engine were analyzed. The ignition for each operating mode occurred between the second pilot injection and the main injection. For every two adjacent modes varying with COHR, the crank angle intervals of the fuel injection timings as well as center of heat release and the location of heat release peak were almost identical. With the increase of COHR, the duration in crank angle taken from injection timing to ignition became shorter, while the duration in the crank angle taken from ignition to the center of the heat release became longer. As compared with the location of a peak pressure in-cylinder, the COHR would be moved backward far away. As for D10 fuel, because the easy vaporization of dimethyl carbonate promoting the mixing of fuel and air and combustion, both crank angle intervals, from the ignition to 10% of heat release and from ignition to 90% of heat release, were shorter, which indicated that the added dimethyl carbonate could help to promote the combustion process. These analyses of combustion features based on COHR will provide a fundamental guidance for the application of dimethyl carbonate/diesel blends, multiple injections regulating the combustion process, and emission control theory. [ABSTRACT FROM AUTHOR]

Biodiesel, as a renewable alternative fuel, is easily crystallized at low temperature, which limits the application of engines fueled with biodiesel. Biodiesel is mainly composed of methyl palmitate (C16:0), methyl stearate (C18:0) and methyl oleate (C18:1). The properties of fuel are closely related to the properties of its compositions, and the fuel properties will change with different mole fraction ratios of some composition. So, it is very important to research the thermal parameters of different compositions. Differential scanning calorimetry (DSC) is a thermo analytical technique by which the difference in the amount of heat required to increase the temperature of a sample and reference is measured as a function of temperature. The result of a DSC experiment is a curve of heat flux related to temperature or time. Through this curve, it is easy to determine transition temperatures and enthalpies, which makes DSC a valuable tool in producing phase diagrams for various chemical systems. Based on the differential scanning calorimeter, thermal parameters of the three methyl esters have been analyzed. The melting point and fusion enthalpy of saturated fatty acid esters (C16:0 and C18:0) are much higher than the ones of unsaturated fatty acid ester (C18:1), the melting points of C16:0, C18:0 and C18:1 are 301.57, 310.92 and 255.01 K, respectively. The binary solution of fatty acid methyl esters has also been scanned, where each curve exhibits two distinct exothermic peaks. These phenomena can be explained in that the high melting point saturated ester precipitated first and the low melting point unsaturated ester precipitated later. Moreover, the crystallization temperature of these solutions is lower than the melting point temperature of the pure saturated fatty acid esters, which precipitated earliest in the solution. It is also clear that the solution crystallization temperature rises accordingly, because the increase of the mass fraction of saturated fatty acid esters. Supposing that biodiesel is a solution combined with different fatty acid methyl esters, the saturated fatty acid esters C16:0 and C18:0 are treated as solutes and the unsaturated fatty acid ester C18:1 is played as solvent, thus the thermodynamic model for calculating the crystallization temperature of the solution has been established. While predicting the crystallization temperature, the solution of fatty acid esters has been dealt with further as an ideal solution; because it just looks at liquid composition as the ideal solution and solid phase composition as not mutually soluble, the model has been simplified. The crystallization temperature of the four different kinds of biodiesel has been calculated by this simplified model, and also has acquired effective verification as compared with the experimental data. [ABSTRACT FROM AUTHOR]

In order to conduct research on the in-cylinder spray and combustion of an electrically controlled high pressure common-rail diesel engine, taking one high pressure common-rail diesel engine as the research object, a multifunctional dynamic visual experimental device was designed, which was used to collect in-cylinder dynamic combustion process images. On this basis, the intake port of the diesel engine was improved, and the fresh air was replaced by industrial purity nitrogen, so that the real-time dynamic multiple spray images were collected under single cylinder misfiring conditions. The study illustrated that the multiple injections-pre- injection, main injection, and post injection-can be clearly observed, including at the injection time, spray cone angle, and in the atomization situation. The pre-injection occurred at the -25° crankshaft angle, and the duration was about 5° crank angle. At this stage, the quantity of fuel injection was less, and the atomization was not obvious. The main injection occurred at the -10° crankshaft angle, and the duration was about 10° crankshaft angle. There was a large amount of fuel ejected from the nozzle, and the penetration force was strong. The spray cone angle and a significant oil beam could clearly be observed, which expanded to the bottom of the piston "ω" crown in line. The post injection occurred at the 8° crankshaft angle, the injection duration was shorter, and the amount of fuel injection was less, however, the atomization effect was obvious because of the higher temperature of the cylinder at this stage. In addition, when the diesel engine ignited, the flame center formation and flame propagation process could be captured in real time under different working conditions. The fuel spray was not fully discrete and mixed with air partly at the initial in-cylinder ignition time, which was the so-called pre-mixing ignition and occurred at -15°- -4° crankshaft angle. Near the TDC, the flame quickly spread and filled the combustion chamber fully along with the air flowing. Compared with the in-cylinder combustion image under rated conditions, the ignition time under idling conditions was delayed about 5° crankshaft angle, the flame occupied area was smaller, and there was lower brightness. The study provided a lot of in-cylinder information and experimental measurement means for research on the in-cylinder spray and combustion of an electronically controlled common-rail diesel engine, and the spray and combustion simulation results could also be verified by these experiments. [ABSTRACT FROM AUTHOR]