Abstract
The tests were carried out with a Euro 2 emission level Volvo bus engine without a catalyst, with an oxidation catalyst and with a CRT particulate trap. The vegetable oil esters studied were rapeseed methyl ester (RME), soy bean oil methyl ester (SME) and used vegetable oil methyl ester (UVOME). RME and SME were tested as 30% blends in European grade diesel fuel and as neat esters. RME was also blended (30%) into reformulated diesel fuel. The test fuel matrix also included Canadian diesel fuel blended with 10% hydrated tall oil and an emulsion of reformulated diesel and some 15% ethanol.
Compared to hydrocarbon fuels, the bioesters reduced CO end HC emissions in most cases. Adding 30% ester in the European fuel did not affect the NOx emission significantly, whereas neat ester resulted in an increase of around 10% in the NOx emission. The effect of esters on the formaldehyde emission was not significant. The ethanol blend reduced NOx and PM emissions compared with the European grade fuel. Clear reductions in PM emissions were noted with bioesters. Using bioesters effectively reduced the black carbon portion of particulate matter. Significant PM reductions were achieved when combining bioester fuels and an oxidation catalyst. The PM emission level with the CRT catalyst/trap was too low to draw conclusions of the effect of fuel.
A reduction in PAH emissions was observed for the bus engine without the catalyst when esters replaced the European grade fuel. The PAH emission level with the aftertreatment devices was so low that no effect of fuel was seen.
Ames test showed that neat esters reduced the mutagenicity of particulate SOF compared to the European grade fuel in the tests with and without oxidation catalyst. The effects of the 30% ester blends and the ethanol blend were not significant. The oxidation catalyst reduced the mutagenicity of particulate SOF, except for reformulated fuel and its blend with RME, which had low levels regardless of the aftertreatment applied. The CRT particulate filter gave no significant benefits regarding the mutagenicity of particulate SOF compared to the tests without catalyst. This might be explained by the formation of nitro-PAH compounds.
Particle size distribution was studied with the bus engine without catalyst. RME resulted in lower mass of particulates in the main peak area (around 0.1 µm) than European grade or reformulated fuels. The number of particles below 56 nm was lower for RME than for the European grade fuel. However, the lowest number of particles in that range was observed for the reformulated fuel.