Investigation on the hydrocarbon adsorption performance enhancement of the ZSM-5 zeolite with different Si/Al ratio in the cold start process of the gasoline engine

Abstract

In response to the issue of hydrocarbon emissions during the cold start process of gasoline engines, a hydrocarbon catcher coated with ZSM-5 zeolite was manufactured. The post-treatment system of the prototype vehicle was modified to install the hydrocarbon catcher, and cold start experiments on the vehicle under World Light-vehicle Test Cycle (WLTC) conditions were conducted. The experimental results showed that the hydrocarbon emissions in the low-speed stage of WLTC were much higher than those in other stages. In the early stages of cold start, the hydrocarbon catcher can reduce hydrocarbon emissions by up to 61 %. The analysis results of engine emissions showed that the content of various hydrocarbon components during cold start was: 60.1 % butene, 13.6 % acetylene, 11.3 % propylene, 7.3 % ethylene, 7.1 % acetaldehyde, and 0.6 % other components. Further molecular simulation studies were conducted on zeolite of different types and Si/Al ratios. The results showed that the adsorption of hydrocarbons on pure Si-MFI and -FER zeolites were less affected by H2O and CO2, making them ideal hydrocarbon capture materials. Al substitution introduced compensating cations into zeolite, which increased the adsorption capacity of H2O, CO2, and C2H4O with polar functional groups. Reducing the degree of Si/Al substitution is beneficial for hydrocarbon adsorption.