Effects of short chain aromatics in gasoline on GDI engine combustion and emissions

Aromatics are parts of the main components in gasoline which play important roles in affecting engine performances. Short carbon chain aromatics (C-8/C8-) takes more part of aromatics in gasoline. In this paper, the effects of toluene, ortho-xylene and ethylbenzene on engine combustion, emission and thermal efficiency are experimentally investigated. Gasoline and three quinary gasoline model fuels containing each of these three aromatics, with diisobutylene, cyclohexane, isooctane, n-heptane being the other four components, are used to support this research. Results show that all the aromatics favor engine combustion and particulate emission while aggravate THC and CO emissions. Toluene, ethylbenzene and ortho-xylene do not obviously affect NOx emission under lower engine speed. However, ethylbenzene and ortho-xylene elevate engine NOx emission much more than toluene does under higher engine speed conditions. Alkenes and alkanes take the vast majority of VOC emission, followed by aromatics and aldehydes. Yet, alkenes take the most responsibility on OFP followed by aldehyde, and then aromatics, alkanes. Ethylene is the major composition of alkenes while formaldehyde contributes the most to aldehydes emission. In compare, toluene would propel alkenes and aldehydes in VOC emissions more than ethylbenzene and ortho-xylene do, however, it greatly alleviates particulate emission. Toluene tends to improve thermal efficiency under low engine speed conditions while ortho-xylene and ethylbenzene improve it under higher engine speed conditions. Results from this paper indicates that short chain aromatics affect engine combustion and emission a lot. So, varying short chain aromatics in gasoline fuel is of great importance in adjusting fuel properties.