Effects of the ZSM-5 zeolites on hydrocarbon emission control of gasoline engine under cold start

The feasibility of ZSM-5 zeolite for controlling hydrocarbon (HC) emissions during cold start period of gasoline engine was studied by temperature programmed desorption (TPD) experiment and molecular simulation (MS). Acetylene, 1-butene, propylene, ethylene, acetaldehyde and benzene molecules were selected as representative HCs based on the HC emission components of gasoline engine cold start experiment. TPD experiment was carried on commercial ZSM-5, and desorption intensity curve of ZSM-5 zeolite for main cold start hydrocarbons was obtained. TPD results indicated that ZSM-5 zeolite can retain most of the hydrocarbons after 472 K, and the overall desorption intensity on ZSM-5 zeolite is acetaldehyde>1-butene > acetylene. Then adsorption and diffusion properties of the six main cold start hydrocarbon components on Na-ZSM-5 zeolite with different Si/Al ratio were studied by grand canonical Monte Carlo (GCMC) method and canonical ensemble Molecular Dynamics (MD) method. The results showed that the adsorption and diffusion of single-component hydrocarbons on ZSM-5 zeolite were affected by the number of exchange cations of zeolite, environment temperature, diameter of HC molecules and covalent bond types of HC molecules, and the adsorption capacity and diffusion coefficient were also affected by the competitive effect between the HC components. In competitive adsorption, molecules with large diameters such as acetaldehyde, 1-butene and benzene occupied the main adsorption sites of zeolite, so the adsorption capacity of these three HC molecules was large, while the adsorption capacity of smaller molecules such as ethylene, acetylene and propylene were small.