The emissions from vehicles in real world driving are of current concern, as they are often higher than on legislated test cycles and this may explain why air quality in cities has not improved in proportion to the reduction in automotive emissions. This has led to the Real Driving Emissions (RDE) legislation in Europe. RDE involves journeys of about 90km with roughly equal proportion of urban, rural and motorway driving. However, air quality exceedances occur in cities with urban congested traffic driving as the main source of the emissions that deteriorate the air quality. Thus the emissions measured on RDE journeys may not be relevant to air quality in cities. A Temet FTIR and Horiba exhaust mass flow measurement system was used for the mass emissions measurements in a Euro 4 SI vehicle. A 5km urban journey on a very congested road was undertaken 29 times at various times so that different traffic congestion was encountered. Each journey was split into ten sections in order that the location and traffic conditions of the highest emissions could be determined. It was found that low speed stop-start traffic has much higher emissions than for freely moving traffic and most of the higher emissions on the longer 5km journeys occurred in relatively short sections of slow moving stop/start traffic. The journey used passed a roadside air quality monitor that exceeded the EU NO2 and PM standards on an annual basis and it was located by the most congested part of the route, where the traffic emissions are shown in this work to be at their highest.
The tailpipe exhaust emissions were measured under real world urban driving conditions by using a EURO4 emissions compliant SI car equipped with an on-board heated FTIR for speciated gaseous emission measurements, a differential GPS for travel profiles, thermocouples for temperatures, and a MAX fuel meter for transient fuel consumption. Emissions species were measured at 0.5 Hz. The tests were designed to enable cold start to occur into congested traffic, typical of the situation of people living alongside congested roads into a large city. The cold start was monitored through temperature measurements of the TWC front and rear face temperatures and lubricating oil temperatures. The emissions are presented to the end of the cold start, defined when the downstream TWC face temperature is hotter than the front face which occurred at ~350-400 o C. Journeys at various times of the day were conducted to investigate traffic flow impacts on the cold start. The test route had traffic and pedestrian crossing lights, several major road junctions and a busy shopping area. The time aligned vehicle moving parameters with pollutant emission data and fuel consumption enabled the micro-analysis of correlations between these parameters. The average cold start emissions, fuel consumption and temperature data are presented for the journeys into different levels of congestion (based on the mean speed of the cold start journey). The mean complete journey speed during was shown to reasonably correlate the emissions, which increased as mean speed reduced. The cold start congested traffic portion was separately analysed to show the much higher emissions for equivalence mean speeds. Engine vehicle specific power (VSP) output was calculated and used together with the fuel flow to determine the instantaneous and average thermal efficiency. Three way catalysts (TWC) light off was approximately 200 seconds, much longer than for the NEDC test cycle. Currently urban air quality monitoring does not include cold start into congested traffic from vehicles at houses along the road, but does have procedures where cold start occur at large car parks.
The tailpipe exhaust emissions were measured using a EURO4 emissions compliant SI car equipped with on-board measurement systems such as a FTIR system for gaseous emission, a differential GPS for velocity, altitude and position, thermal couples for temperatures, and a MAX fuel meter for transient fuel consumption. Various nitrogen species emissions (NO, NO2, NOx, NH3, HCN and N2O) were measured at 0.5 Hz. The tests were designed and employed using two real world driving cycles/routes representing a typical urban road network located in a densely populated area and main crowded road. Journeys at various times of the day were conducted to investigate traffic conditions impacts such as traffic and pedestrian lights, road congestion, grade and turning on emissions, engine thermal efficiency and fuel consumption. The time aligned vehicle moving parameters with Nitrogen pollutant emission data and fuel consumption enabled the micro-analysis of correlations between these parameters. The average data for journeys such as thermal efficiency, emissions and fuel consumption were determined. Traffic events and vehicle transient movements' impact on emissions were studied. Engine power output has been calculated by using vehicle specific power (VSP). The analysis result of tailpipe emissions and their relation to real world driving profile improved understanding of urban area nitrogen compound emissions, which will be useful for controlling of urban air quality.
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