Phenomenology of EGR in a Light Duty Diesel Engine Fuelled with Hydrogenated Vegetable Oil (HVO), Used Vegetable Oil Methyl Ester (UVOME) and Their Blends

HVO contains paraffin only and UVOME is methyl ester with long chain alkyl while mineral diesel is complex compound and contains lots of aromatic and Naphthenic. This paper compares the effects of EGR on the two different types of biodiesels blends compared to diesel. The combustion performance and emissions of biodiesel blends of UVOME and HVO were investigated in a turbocharged direct injection V6 diesel engine with EGR swept from 0% to the calibration setting for diesel. The EGR sweep tests with increment of 5% were conducted at the engine speed of 1500 RPM for the load of between 72 Nm to 143 Nm, using sulfur-free diesel blended with UVOME and HVO at 30% and 60% by volume respectively. As the EGR rate was increased, the brake specific fuel consumption (BSFC) for each fuel was reduced at lower load but increased at higher load. The BSFC of mineral diesel was lower than UVOME blends and similar to the HVO blends. NOx emissions were reduced with increasing EGR percentage for all fuels tested at all engine loads while the emission levels were similar except HVO60 which produced less NOx with low EGR rate. The smoke emissions were affected by EGR in different extensions. At low EGR rate (≺15%), the smoke emission of each fuel was maintained and sometimes even a little decreased. At medium EGR rate (between 15% and 35%), the smoke emission was increased dramatically as EGR rate increased. At high EGR rate (≻35%), the smoke emission of HVO blends kept increasing as EGR rate increased while the increase rate of other fuels slowed down and decreased at last.