RDE-based assessment of a factory bi-fuel CNG/gasoline light-duty vehicle

Abstract

On-road exhaust emissions of a Euro 5 factory bi-fuel CNG/gasoline light-duty vehicle equipped with the TWC were assessed considering the Real Driving Emissions (RDE) guidelines. The vehicle was equipped with a Portable Emission Measurement System (PEMS) that enabled the measurement of THC, CO, NOx, CO2, and CH4. With respect to the characteristics of the vehicle, the appropriate Worldwide Harmonized Light-Duty Vehicle Test Cycles (WLTC) were selected and based on the requirements of the RDE legislation a suitable route was conceived. In addition to the moderate RDE-based route, an extended RDE-based route was also determined. The vehicle was driven along each defined route twice, once with each individual fuel option and with a fully warm vehicle.RDE routes feature a multitude of new driving patterns that are significantly different to those encountered in the NEDC. However, as these driving patterns can greatly influence the cumulative emissions an insight in to local time trace phenomena is crucial to understand, reason and to possibly reduce the cumulative emissions. Original contributions of this paper comprise analyses of the RDE-LDV local time resolved driving emissions phenomena of a CNG-powered vehicle that are benchmarked against the ones measured under the use of gasoline in the same vehicle and under similar operating conditions to reason emission trends through driving patterns and powertrain parameters and exposing the strong cold-start independent interference of CO and N2O infrared absorption bands in the non-dispersive infrared (NDIR) analyzer. The paper provides experimental evidence on this interference, which significantly influences on the readings of CO emissions. The paper further provides hypotheses why CO and N2O interference is more pronounced when using CNG in LDVs and supports these hypotheses by PEMS tests.The study reveals that the vehicle's NOx real-world emission values of both conceived RDE-based routes when using both fuels are within Euro 5 and type-approval limits. Additionally, the THC and the NMHC emissions of both RDE-based routes using both fuels are within the Euro 5 limits indicating reasonable CH4 emissions. Notable increases above the type-approval and Euro 5 limits appeared in the CO emissions profile when using gasoline, while the CO2 emissions profile expectedly also exceeded the type-approval specifications.