Diesel Cold Start into Congested Real World Traffic: Comparison of Diesel and B100 for Ozone Forming Potential

EU environmental law requires 30 ozone precursor volatile organic compounds (VOCs) to be measured for urban air quality control. In this study, 28 ozone precursor VOCs were measured at a rate of 0.5 Hz by an in-vehicle FTIR emission measurement system along with other VOCs. The vehicle used was a Euro 3 emission compliant diesel van. The test vehicle was started from a cold ambient temperature soak and driven under real world urban driving conditions. Diesel and B100 (100% Biodiesel) were compared using the same repeat journeys. The VOC emissions and OFP (ozone formation potential) were investigated as a function of engine warm up and ambient temperatures during cold start. The exhaust temperatures were measured along with the exhaust emissions. The temperature and duration of light off of the catalyst for VOC were monitored and showed a cold start period to catalyst light off that was considerably longer than would occur on the NEDC (New European Driving Cycle). The results showed that compounds that formed ozone were significantly higher in diesel exhausts and were higher than equivalent compounds in SI vehicles under cold start in real world urban driving. For B100 aldehyde emissions were higher than for diesel and this is a strong ozone forming gas. However, other VOCs that form ozone were lower than diesel. The higher VOCs with diesel compared to SI engines was mainly due to the oxidation catalyst not being active for much of the journey, whereas in SI engines VOC emissions were only significant during the cold start period. The results will also be shown to be dominated by transient events at junctions and by the cold start period