Abstract
Abstract. Existing ultra-fast response engine exhaust emissions analyzers have been adapted for on-board vehicle use combined with GPS data. We present, for the first time, how high spatio-temporal resolution data products allow transient features associated with internal combustion engines to be examined in detail during on-road driving. Such data are both useful to examine the circumstances leading to high emissions, and reveals the accurate position of urban air quality “hot spots” as deposited by the candidate vehicle, useful for source attribution and dispersion modelling. The fast response time of the analyzers, which results in 100 Hz data, makes accurate time-alignment with the vehicle's engine control unit (ECU) signals possible. This enables correlation with transient air fuel ratio, engine speed, load, and other engine parameters, which helps to explain the causes of the emissions “spikes” that portable emissions measurement systems (PEMS) and conventional slow response analyzers would miss or smooth out due to mixing within their sampling systems. The data presented is from NO and NOx analyzers, but other fast analyzers (e.g. total hydrocarbons (THC), CO and CO2) can be used similarly. The high levels of NOx pollution associated with accelerating on entry ramps to motorways, driving over speed bumps, accelerating away from traffic lights, are explored in detail. The time-aligned ultra-fast analyzers offer unique insight allowing more accurate quantification and better interpretation of engine and driver activity and the associated emissions impact on local air quality.
Highlights
Urban air quality is of current concern in many of the world’s cities (Mayer, 1999; Chan and Yao, 2008), with a particular focus on the health effects of particulate and NOx emissions (Samet et al, 2000; Kampa and Castanas, 2008), and governments are facing punitive fines for breaching agreed air quality limits (Secretary of State for Transport, 2016)
Portable emissions measurement systems (PEMS) have been developed by a number of manufacturers to comply with the latest EU emissions regulations (EU Commission, Article 2016/427, 2016) but their response times are of the order of 1 s, with a further “delay time” owing to the transit time of sample gas from its source to the analyzer
Mass air flow (MAF) data have been used when available from the engine control unit (ECU), and where MAF data are not available from the ECU it has been calculated using intake air temperature, engine speed, manifold pressure, the dimensions of the engine, air / fuel ratio, and an estimation of volumetric efficiency based on empirical calculations
Summary
Urban air quality is of current concern in many of the world’s cities (Mayer, 1999; Chan and Yao, 2008), with a particular focus on the health effects of particulate and NOx emissions (Samet et al, 2000; Kampa and Castanas, 2008), and governments are facing punitive fines for breaching agreed air quality limits (Secretary of State for Transport, 2016). Portable emissions measurement systems (PEMS) have been developed by a number of manufacturers to comply with the latest EU emissions regulations (EU Commission, Article 2016/427, 2016) but their response times are of the order of 1 s, with a further “delay time” owing to the transit time of sample gas from its source to the analyzer Their response times are further compromised by the additional pipe volumes required to support the exhaust mass flow measurement system such that the resulting response time makes the emissions data difficult to align accurately with ECU and spatially accurate GPS data. The technique which will be discussed in this paper is the instrumentation of ultra-fast gas analyzers for tailpipe sampling and the identification of urban road features conducive to producing high emissions for multiple vehicles This data could be used by city councils or planning authorities to improve current road layouts or influence future developments to improve urban air quality
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