Diesel Cold Start into Congested Real World Traffic: Comparison of Diesel, B50, B100 for Gaseous Emissions 2013-01-2528

A cold start Euro 3 1.8 litre Diesel vehicle with an oxidation catalyst was used to investigate real world exhaust emissions over a driving cycle that included urban cold start congested traffic driving conditions. The aim was to identity those aspects of cold start real world driving responsible for higher emissions than in test cycles. Higher real world emissions may contribute to the problem of air quality in urban areas, which has not improved in quality in proportion to the reduced in vehicle exhaust emissions. Diesel, B50 and B100 fuel were compared to determine if real world driving effects were worse for B50 and B100 fuels due to their lower volatility and higher viscosity. The biofuel was WRME, derived from waste rape seed cooking oil. A multifunctional additive package was added to the biofuel at 800ppm to control fuel injector deposit formation. Gaseous emissions were monitored using an on-board heated Temet FTIR exhaust emission analyzer. The catalyst front and rear temperatures were monitored and this showed a cold start period to catalyst light off that was considerably longer than would occur on the NEDC. This was due to the time from cold start to the occurrence of a significant acceleration and 30 km per hour velocity, with hot exhaust gases, was much longer than the 11s in the NEDC. CO and UHC emissions were high throughout this cold start period. The results show that CO, THC and NOx emissions exceeded the EURO 3 exhaust emission legislation in real world driving, due to the longer cold start and the presence of more stop/start actions than in the test cycles. The average B50 and B100 CO emissions were 20% higher than diesel. The THC emissions were 32% higher than diesel for B50 and 360% higher for B100. Cold starts catalyst light off were similar for the three fuels and hence the higher THC and CO emissions indicate worse atomization and mixing in the fuel spray that resulted in higher engine out emissions with B50 and B100. Mean NOx emissions were 23% higher for B50 and 38% higher for B100 compared with diesel. All fuels produced NOx emissions that were much higher than the legislated value, which was mainly due to the presence of more stop/start events followed by hard accelerations. This was due to the proportionality between NOx and power and acceleration rates. Most of this increase was due to NO as NO₂ emissions were similar for all three fuels. Diesel had significantly higher emissions of N₂O than B50 or B100. CO and THC emissions were much higher than for the legislated cycle as most of this work was carried out with a cold start and the oxidation catalyst was not active for most of the journey.