Time Alignment For Real Time Measurement

Time Alignment Time Alignment is an important factor in the calculation of mass emissions from vehicles operating under transient conditions from raw exhaust measurements Key parameters include :- speed of response of the exhaust flow measurement speed of response of the exhaust analysers corrections for water content differences between exhaust flow rate and measured concentrations (exhaust flow is usually wet base, analysers can be wet or dry base) Analyser interferences can be an issue Ambient corrections to be considered (Nox correction, altitude)

HORIBA study on time alignment EXSA-240 flow configuration Response Time EXSA-240 Nox/O2 analyser Speed of response

Nox is the main issue (EPA-505)

Other gases are not so sensitive - CO2

CO

HC - NDIR

OBS Time Alignment OBS has freely adjustable time delays. Current setting is Td + T50 A check utility will be included to measure Td T50 and T90 in the future software for the OBS-2000 series

OBS Mass Calculations

Standard Mass Calculation Mass Emissions Mass = Exhaust_Flow * Concentration * Density Where Exhaust flow = litres @20 deg C / 101.3 kPa Concentration = ppm/10e6 Density = standard densities (CFR) in g/litre @20 deg C/101.3 kPa Mass is calculated in 10 Hz basis and integrated OBS-1000 does NOT correct the Nox mass for the Nox engine air humidity (Nox correction factor)