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Diesel Cold Start into Congested Real World
Traffic: Comparison of Diesel and B100 for Ozone Forming Potentia
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比较柴油和B100对臭氧形成潜在作用的大小。
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
Transport related hydrocarbon emissions have three major health and environmental impacts: ozone forming potential(OFP), toxicity and greenhouse effect.
Ozone is an irritant gas that affects eyes, nose and lungs and reduces the lung function and triggers asthma attacks.
For the control of ground ozone concentrations in urban areas, the EU has set up the environmental law that requires 30 individual OFP precursor VOCs and NMHC (non-methane Hydrocarbons) to be measured.
Although there is no requirement to measure
ozone precursor emissions from passenger car exhaust, one of the principle reasons for the development of NOx and UHC vehicle emissions regulations is to control the formation of ozone and other component of photochemical smog
The interest in the VOC emission measurement is increasing as it is an important indicator for the OFP
The VOC emissions are affected by the driving mode and pattern, engine types and fuels etc. Li et al. investigated VOC and OFP for SI engine vehicles in real world driving
The work showed that for a warmed up catalyst there were low level pulses of VOCs at every lean excursion during transients at road junctions
However, the worst problem was under cold
start where emissions were very high during
the cold start period and that once the TWC was ho(gt;400°C) there was little increase emissions of VOCs,relative to the cold start levels.
The problem of VOC emissions during cold start in real world driving was also part of the general problem of all emissions being higher during cold start, coupled with cold start being longer in real world driving [4, 5]. The cold start effect on VOC emissions was also investigated by Lea-Langton et al  for a PerkinsPhaser TCIC DI diesel engine on a dynamometer.
They showed that VOC emissions were dominated by the cold start emissions and that the oxidation catalyst light off time was a
key parameter in determining these cold start emissions.
Windeatt et al.  have carried out preliminary work on cold start emissions for diesel fuels using the same real world test cycle as in the present work.
This showed a much smaller cold start influence on emissions than for spark ignition
engines and also showed that after the first minute of cold start the gaseous emissions for the warm engine were dominated by transient events associated with junctions.
Apart from cold start influence, the introduction of biofuel is another important factor affecting VOC emissions and OFP.
As the share of biofuels in transport is set to increase in the EU, the effect of biofuels on VOC emissions and OFP has an ever increasing importance.
The EU has legislated for all diesel sold in Europe to contain biofuels with a proportion of 2% in 2005, inc