The exhaust emissions produced by the combustion of methyl ester of rapeseed oil (biofuel) have been compared with the ones obtained using a commercial diesel fuel. The tests have been carried out on a Direct Injection Turbocharged (DITC) diesel engine according respectively to the ECE 15, to a non standard STOP and GO test cycle and to the European 13 MODE test procedure. Similar engines running at the same injection timing have been adopted in performing the transient and the steady tests. PAH emissions have been measured on transient cycles.
The effects of injection timing and of Exhaust Gas Recirculation (EGR) on the emission in steady state tests has been evaluated too. In particular an exhaust oxydating catalyst has been employed in presence of EGR.
The tests carried out indicate that, at the same injection timing, methyl ester promotes a rise in NOx emission, a decrease in HC and CO as well as a strong reduction of smoke. Particulate matter produced by methyl ester in transient cycles is higher than that obtained with diesel fuel. Anyway a general trend to the PAH reduction has been recognized.
Finally experiments have shown that NOx, HC and CO emission of biofuel may be reduced, with low effects on particulate, by the adoption of EGR in presence of an exhaust oxydating catalyst.