A fuel matrix consisting of twelve gasolines was tested in presence of Exhaust Gas Recirculation (EGR). The fuels have different percentages of aromatics (20÷35% vol.), olefins (5÷15% vol.) and oxygen (0÷2% wgt). Four different oxygenated compounds (MTBE, ETBE, TAME, DIPE) were chosen as additives.
Tests were carried out on a MPI premixed spark ignition engine at steady operating conditions (2000 rpm, 2 bar BMEP, 13.5% EGR) and stoichiometric air/fuel ratio. Regulated and unregulated pollutants were measured upstream the catalytic converter. Cyclic variation of Indicated Mean Effective Pressure (IMEP) in presence of EGR was also evaluated.
The adoption of EGR increases PAH and aldehydes emissions, and decreases benzene emissions of unoxygenated fuels. Conversion efficiencies of CO and of total HC are lowered by EGR. An increase of aromatics content in an unoxygenated fuel leads to higher engine out NOx emission. This effect is reduced if MTBE is added. In presence of EGR, the addition of oxygenated compounds as MTBE, ETBE, TAME, DIPE reduces 1-3 butadiene emission but it can increase aldehydes.