The recent particle number limits for a spark ignition engine combined with the real driving emissions (RDE) compliance have motivated the need for a better understanding of the effect of the gasoline fuel composition on the particle emissions. More particularly, the fundamental role of high boiling point components and heavy aromatics on particle emissions was highlighted in several literature works. In addition, works driven by the European Renewable Energy Directive are underway in order to explore the feasibility of an increased amount of sustainable Biofuels in Gasoline. Already widely distributed, ethanol is a clear candidate to such an increase.
In this context, the present work aims to understand the effect of ethanol addition and aromatics composition on particulate emissions.
Vehicle tests were performed over the Worldwide Harmonized Light Vehicles Test Cycle (WLTC) using a Euro 6c model without a Gasoline Particulate Filter (GPF) and a Euro 6d-Temp one equipped with a GPF. Both are Gasoline Direct Injection vehicles. Particulate emissions measurements were performed using E10 Euro VI reference fuel and nine different fuel blends containing between 10% and 40% of ethanol and 17% to 35% of aromatic hydrocarbons by volume.
Results confirm the positive effect of Ethanol addition on particle number with aromatic dilution. On the contrary, by adding ethanol and by maintaining the same fraction of aromatics through a simultaneous addition of both components, no significant difference in particle numbers was observed.
The Smoke Point (SP) is a standard fuel property that represents the sooting tendency in diffusion flame. SP was successfully measured in this study on all the investigated fuels and was compared to particle numbers from vehicle test measurements.
The Honda Particulate Matter Index (PMI) proposed by Aikawa et. al and other fuel indices were also evaluated in terms of agreement with vehicle test bed results.
For the cases with aromatic content variations, the high sensitivity of PMI index to hydrocarbons content leads to a good agreement with vehicle test results. However, for mixtures with simultaneous addition of aromatics and ethanol, the PMI indices do not exhibit a good correlation with vehicle test measurements. Measured SP exhibit the best correlation with particle numbers and concentrations results when compared to the fuel indices.