Baumann, P., Schroeder, M., Kurz, H., Maier, T. et al., "Investigation of the Influencing Parameters Using Optimized Exhaust Emissions Measurement Systems with Different Modern Plug-in Hybrid Electrical Vehicles," SAE Technical Paper 2015-01-1069, 2015, doi:10.4271/2015-01-1069.
The variety of increasingly complex powertrains including Plug-In Hybrid Electric Vehicles (PHEVs) is associated with a number of challenges to measure exhaust gas emissions: Although the conventional constant volume sampling (CVS) and exhaust gas measurement systems remain a high precision emission measurement concept new questions occur that need to be answered, such as mass transport, catalyst cooling during ICE-off and emission measurement accuracy.Mass transport of exhaust emissions from the transfer tube into the dilution tunnel during engine-off complicates phase assignment. This includes the investigation of the physical processes that are diffusion on basis of concentration differences, extraction due to the CVS underpressure and convection because of density diversities.Catalyst cooling will be investigated using a temperature sensor positioned at the oxy catalyst of a Diesel-PHEV. This involves analyzing the catalyst temperature change during engine-off phases and evaluating the emission of pollutants after the engine restarts during a driving cycle.Emission measurement accuracy is influenced since PHEV are partially operated with the electric motor during a driving cycle, or switched off while idling. Therefore concentrations of gaseous components in the diluted exhaust batches are decreasing, which causes an increase in analysis error. In order to reduce measurement errors an alternative measurement procedure “During Test Top Off” (DTTO) has been developed: with this procedure the batches are only filled when the combustion engine is operated - or near the end of a driving cycle to sample enough batch volume for an accurate analyzer reading. The results will show if this alternative procedure can improve measurement errors and thus complies with the error limits of the European emission regulations.