Assessment of On-Board and Laboratory Gas Measurement Systems for Future Heavy-Duty Emissions Regulations

Abstract

Road transport contributes significantly to air pollution in cities. Regulations across the globe continuously reduce the limits that vehicles need to respect during their lifetimes. Furthermore, more pollutants are being subject to control with new regulations and, most important, testing tends to be done under real-world conditions on the road. In this study, various portable systems were compared with laboratory-grade equipment with a wide range of emissions, focusing on the lower end, where the measurement uncertainty of the instruments is crucial for the determination of emission limits. The engines were diesel- and compressed natural gas (CNG)-fueled. The results were promising, with relatively small differences between portable emissions measurement systems (PEMSs), portable Fourier transform infrared (FTIR) and quantum cascade laser infrared (QCL-IR) spectrometers, and the respective laboratory-grade analyzers based on chemiluminescence detection (CLD), non-dispersive infrared (NDIR), and FTIR principles. The results also highlighted the need for strict technical regulations regarding accuracy and drift for low emission limits in future.

Measurement of Light-Duty Vehicle Exhaust Emissions with Light Absorption Spectrometers

“…For NH 3 , the humidity in the exhaust gas plays an important role, as it condensates on the tubing, sampling probes, and sampling lines of the instruments, where NH 3 can be adsorbed and later released (see Appendix A, Figure A2). The 10% difference is acceptable and in agreement with the literature [32,69]. Even though the calibration of the instruments can be much more accurate, the dynamic phenomena described previously play an important role.…”

“…A closer look at the data reveals that the two instruments at the tailpipe (FTIR and NDIR instruments) were within 5 g/km or 5%, further supporting that the remaining 5% differences from the dilution tunnel instrument were mainly due to uncertainties in the exhaust flow determination. Nevertheless, 5-10% differences in CO2 measurements are acceptable and of the same order of values in other studies with similar technologies [32,69,77,97,[109][110][111][112][113].…”

“…FTIR instruments' NO 2 measurement is affected by water vapor interference. Differences of 5-15% have also been reported for instruments measuring light-duty vehicle and heavyduty engine exhaust gas [69,77,[111][112][113]. Studies with light-duty vehicles found differences in instruments of around 10 mg/km for up to 80 mg/km emission levels [97,116] and a 5 mg/km difference for levels of around 15-45 mg/km [114,116].…”

“…QCLs can be designed to emit in the wavelength region from below 4 µm to more than 10 µm. QCLs for N 2 O detection have been studied by many researchers [63][64][65][66][67][68][69][70], but ICLs have also been researched [71]. QCLs for engine exhaust measurements have also been employed for many years [72,73].…”