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Molecular Simulation of the Absorbent Material of Diesel Cold-start Hydrocarbon Absorber

Author: HanWei
Tutor: DengYuanWang
School: Hunan University
Course: Power Machinery and Engineering
Keywords: Diesel Cold-Start Hydrocarbons Zeolites Molecular Simulation
CLC: TK421.5
Type: Master's thesis
Year: 2013
Downloads: 10
Quote: 0
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Abstract


It is expected that the world market for diesel engines will grow significantly inthe near future because of their superior thermal efficiency, durability, and reliabilityin comparison to the gasoline engines. However, the stringent legislation limits forthe amount of pollutants in exhaust gases pose some major challenges for the dieselengines. There will be lots of hydrocarbon emissions in cold-start period release intothe air without an efficient emission control system. Recently, a better solution istrapping hydrocarbons using adsorbent during cold-start and releasing them after thecatalyst has reached its light off temperature. Zeolites are often suggested ashydrocarbon trapping materials due to their hydrothermal stabilities and relativelyhigh adsorption capacities. Therefore, a better understanding of the adsorptionbehaviors of hydrocarbons on adsorbent would help trap the hydrocarbons emittedfrom diesel engines during cold-start period more efficiently.In this paper, we firstly analyze the source of hydrocarbons during cold-startperiod, and propose some appropriate measures to enhance the cold-start performanceof the diesel engine, and establish a simple prediction model of the diesel cold-starthydrocarbon emissions. Secondly, the adsorption behaviors of hydrocarbons in LTA、MFI、 BEA zeolites were studied using Grand Canonical Monte Carlo (GCMC)simulation. The adsorption isotherms and mass clouds are obtained for both purecomponent and binary mixtures under certain temperatures. Then, MFI zeolites withvarious Si/Al rations are investigated. We get some results as follows:1) The adsorption isotherms reveal that the average loading of ethylene andpropylene has the similar trend in LTA、MFI、BEA zeolites under the diesel cold-startcondition. Both of them increase with the increase of pressure and decreasesignificantly with the increase of temperature. We arrange the absorption efficiency asMFI>BEA>LTA, and the adsorption effect of propylene in these three kinds ofzeolites is better then ethylene.2) At298K, the adsorption amount of propylene decreased slightly in MFIzeolite that after modified by Na+, but at398K and498K, the adsorptive capacity ofpropylene increases slightly. For ethylene, the adsorptive capacity increases sharply.The binary mixtures show that propylene and ethylene are both increase in MFIzeolite that after modified by Na+, and the effect on ethylene is remarkable. 3) At298K, with the reduction of ratio of Si/Al, the adsorptive capacity ofpropylene decreases firstly and then increases, and reaches the minimum value atSi/Al=23. On the contrary, the adsorptive capacity of ethylene presents the trend ofgradually increasing, and reaches the maximum value at Si/Al=23. At398K, theadsorptive capacity of propylene reduces slightly along with the Si/Al ratio reduces,but the ethylene adsorptive capacity rises markedly. At498K, the adsorptive capacityof propylene seems to be always changing and fluctuating, and reaches the maximumvalue at Si/Al=23, and the ethylene adsorptive capacity presents the growth tendencyas before.

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CLC: > Industrial Technology > Energy and Power Engineering > Internal combustion engine > Diesel engine > Theory > Emission and purification
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