The ignition delay of n-heptane homogeneous charge compression ignition(HCCI) combustion under high levels of carbon dioxide addition was quantitatively measured at elevated pressure from low to intermediate temperatures in a rapid compression machine.The experiments were conducted in the compressed temperature range 613-750 K.Both the compression ratio and fuel/air equivalence ratio were varied to investigate their effects on the ignition delay of n-heptane.Carbon dioxide was subsequently added to study the influence of the carbon dioxide level on the ignition delay of n-heptane under low-temperature conditions.It was found that carbon dioxide had different effects on the two-stages of ignition delay of n-heptane under low-temperature conditions:the concentration of carbon dioxide had little effect on the first-stage ignition time;a certain concentration of carbon dioxide accelerated the first-stage ignition but had a significantly larger impact on the second-stage ignition delay,thus increasing the overall ignition delay time.The results also showed that the first-stage ignition delay of n-heptane is only a function of temperature under low-temperature conditions.The mass of n-heptane in the combustible mixture,the equivalence ratio,and the pressure at the top dead center had little effect on the first-stage ignition time of n-heptane.
Iodine-modified calcium-based rice husk ash sorbents （I2/CaO/RHA） were synthesized and characterized by X-ray diffraction, X-ray fluorescence, and N2 isotherm adsorption/desorption. Adsorption experiments of vapor-phase elemental mercury （Hg^0） were performed in a laboratory-scale fixed-bed reactor. I2/CaO/RHA performances on Hg^0 adsorption were compared with those of modified Cabased fly ash sorbents （I2/CaO/FA） and modified fly ash sorbents （I2/FA）. Effects of oxidant loading, supports, pore size distribution, iodine impregnation modes, and temperature were investigated as well to understand the mechanism in capturing Hg^0. The modified sorbents exhibited reasonable efficiency for Hg^0 removal under simulated flue gas. The surface area, pore size distribution, and iodine impregnation modes of the sorbents did not produce a strong effect on Hg^0 capture efficiency, while fair correlation was observed between Hg^0 uptake capacity and iodine concentration. Therefore, the content of 12 impregnated on the sorbents was identified as the most important factor influencing the capacity of these sorbents for Hg^0 uptake. Increasing temperature in the range of 80-140℃ caused a rise in Hg^0 removal. A reaction mechanism that may explain the experimental results was presumed based on the characterizations and adsorption study.
Pengfei Zhao,Xin Guoff,Chuguang Zheng State Key Laboratory of Coal Combustion,Huazhong University of Science and Technology,Wuhan 430074,China
