Effect of Fuel Ethanol Content on Exhaust Emissions of a Flexible Fuel Vehicle

Abstract

The European Union is aiming at increasing the market share of biofuels in order to improve the security of supply of transport fuel and to reduce CO2 emissions. The target is to reach a 10% of fuels from renewable sources on energy basis in the transport sector by 2020 and biofuels represent one of the most important options. Bioethanol and biodiesel represent the only biofuels currently available on the market in big quantities and technologically mature. Bioethanol is probably the most broadly employed alternative fuel in the world (mainly in Brazil, USA and Sweden). An experimental program was carried out at the JRC to investigate the emissions of a flexible fuel vehicle using different ethanol/gasoline blends. In this report we will focus on the effect of fuel ethanol content on exhaust emissions from a Flexible Fuel vehicle and on some issues related to the use of bioethanol as transport fuel. The test vehicle was a passenger car currently marketed in Europe and one of the most popular models belonging to the flexible fuel vehicle category. Emission tests were carried out both following the European certification procedure (NEDC cycle) and using a US driving cycle (US 06). Regulated and unregulated emissions were measured. Three different fuels have been tested: a standard commercial summer gasoline marketed in Italy used as base fuel and two gasoline/ethanol blends, which have been obtained by splash blending ethanol in the standard gasoline. The two gasoline/ethanol blends contained respectively 10% ethanol (E10) and 85% ethanol (E85). In general the repeatability of emission measurements was not very good; only with E85 the measured emission levels were very repeatable. The poor repeatability might be linked to the very sophisticated engine management system which modifies the engine settings depending on the ethanol content of the fuel. Nevertheless sound conclusions can be drawn for the NEDC cycle while for the US 06 this is more difficult due to the limited number of tests performed. The results have shown that over the European NEDC cycle the vehicle complies with the Euro 4 emission standards with all the fuel with the only exception of CO with fuel E10. In some cases the CO value measured with fuel E10 resulted to be slightly higher than the limit (1 g/km). CO and HC emissions measured over the NEDC cycle with fuel E10 resulted to be higher than with the other two fuels. On the contrary, E85 was the least emitting fuel as far as these emissions are concerned. The influence of fuel composition was instead almost negligible for NOx emissions. A statically significant increase of NOx emissions was noticed only in the case of E85 and only over the extra-urban part of the NEDC cycle. CO2 emissions were reduced by about 4-6% with fuel E85 both over the NEDC and over the US06 cycle. Similar trends have been found in a recent, major Canadian study, with the only exception that CO emissions were slightly reduced with E10 – a finding that may be explained by the different test cycles. While particulate emissions measured over the NEDC cycle were very low, the PM levels turned out to be quite high over the US 06 cycle. In this case the emissions were comparable to those of a Euro 3 diesel car. This might be due to the very aggressive driving pattern of the US 06 cycle which contains very hard accelerations. In these conditions the engine is likely to work in open loop and with a very rich mixture. The most significant effect of ethanol in the fuel was observed for emissions of carbonylic compounds. This effect increased with increasing ethanol concentration. In particular for acetaldehyde E85 resulted in a more than twenty fold increase in emissions. This represents the main concern associated with the use of flexible fuel vehicles. Comparably with HC emissions, from the speciation of VOCs emissions the fuel E10 resulted to be the most emitting fuel while E85 the least emitting one. E85 resulted in a reduction of 57% of the sum of the speciated VOCs compared to standard gasoline, but with an enrichment of C2 compounds. Emissions of toxic compounds such as benzene and 1,3- butadiene also decreased when E85 was used instead of standard gasoline. Contributions from ethene and propene prevailed regarding the potential of ozone formation.