Comparison of Exhaust Emissions and Particulate Size Distribution for Diesel, Biodiesel and Cooking Oil from a Heavy Duty DI Diesel Engine

Rape oil, as used in fresh cooking oil (FCO), and the methyl ester derived from waste cooking oil (WCOB100) were tested as 100% biofuels (B100) on a heavy duty DI diesel engine under steady state conditions. The exhaust emissions were measured and compared to those for conventional low sulphur (<50ppm) diesel fuel. The engine used was a 6 cylinder, turbocharged, intercooled Perkins Euro2 Phaser Engine, fitted with an oxidation catalyst. The engine out gaseous emissions results for WCOB100 showed a large decrease in CO and HC emissions, but a small increase in NOx emissions compared to diesel. However, for FCO the CO and HC increased relative to WCOB100 and CO was higher than for diesel, indicating deterioration in fuel/air mixing. The particulate matter (PM) emissions for WCOB100 were similar to those for diesel at the 23kw condition, but greatly reduced at 47kw. The FCO produced higher engine out PM at both power conditions due to a higher volatile organic fraction (VOF). FCO was found to have the highest number of nuclei mode particles from the engine, but the greatest reduction across the oxidation catalyst. After the oxidation catalyst both FCO and WCOB100 had lower nuclei mode particle number emissions than diesel in the smallest size ranges measured. This was due to a high proportion of liquid aerosol particles, that were removed by oxidation at the catalyst and the effect of the oxygenates in the FCO and WCOB100 fuels that was to reduce the carbon particulate emissions from the engine.