The equivalence ratio φ and temperature T are well known to have a significant effect on the quality of particulate formation, such as the soot volume fraction, particle diameter and number density. The purpose of this work is to clarify the φ-T dependence of soot formation for various kinds of fuels, including paraffinic hydrocarbon, aromatic hydrocarbon and oxygenated hydrocarbon, and to discuss a possibility for smokeless diesel combustion considering particulate size and number density. The sooting φ-T map, showing the tendency to generate soot particles as a function of φ-T and T, was made using a detailed soot kinetic model. The computational results show that oxygenated fuel reactions lead to a lower soot yield, smaller particle diameter, lower number density and narrower sooting φ-T region than those of aliphatic and aromatic fuels, due to the notable reduction in production of both acetylene and polycyclic aromatic hydrocarbons (PAHs). Furthermore, this lower sooting tendency is emphasized as the fuel oxygen content increases. It was also found that the leaner mixture side of the soot formation peninsula on the φ-T map, rather than the lower temperature side, should be utilized to suppress the formation of PAHs and ultra-fine particles together with a large reduction in particulate mass.
The use of a phase adjuster (PA) has been proposed to improve the cooling effect of a loop-tube-type thermoacoustic cooling system. A PA is a device for increasing the particle velocity of sound by narrowing a part of the loop tube. In this experiment, we present a discussion of the efficiency of heat-to-sound energy conversion in a loop-tube-type thermoacoustic prime mover, particularly emphasizing on the inner diameter change of PA. It is found that the sound pressure is higher for larger inner diameter; the particle velocity is higher for larger inner diameter and the phase difference between the sound pressure and the particle velocity is bigger for larger inner diameter. It is also found that sound intensity is different according to the inner diameter, and that it is higher for larger inner diameter. Results obtained confirm that PA improves the efficiency of heat-to-sound energy conversion in the loop-tube-type thermoacoustic prime mover, and that the efficiency depends on the inner diameter of PA.
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