Investigations of Changes of the 2-Stroke Scooters Nanoparticles in the Exhaust- and CVS-System 2013-24-0178
Nanoparticle emissions of two 2-stroke scooters were investigated along the exhaust and the CVS (Constant Volume Sampling) systems. Two configurations were tested: regular full-flow dilution configuration (denoted as “closed”) and also a modified sampling configuration (denoted as “open”).
The scooters represent two distinct modern technologies. One scooter had direct injection TSDI*) (Two-Stroke Direct Injection). The other had a carburettor. Depending on the technology, the scooters produce different kind of aerosols (state-of-oxidation and SOF content). Moreover, the scooters were operated with and without oxidation catalyst.
The tests were performed at two constant vehicular speeds (20 km/h and 40 km/h). The measuring procedures are those established during the previous research of the Swiss Scooter Network. The nanoparticulate emissions were measured using SMPS (Scanning Mobility Particle Sizer) and DC (Diffusion Charging) sensors.
The most important results are:
The changes of the particle size distributions (PSD) of the aerosol, along the exhaust and CVS systems, are influenced by the average gas temperature and particle count (PC) concentration, which result after the different dilution steps and cooling down in the connecting pipe.
The “open” variant of exhaust gas sampling has a dilution step, with unfiltered ambient air, directly after tailpipe. This stops agglomeration, decreases diffusion losses*) and increases nanoparticle (NP) concentration. There is also lower postoxidation of CO and HC. Some spontaneous condensates, due to the temperature drop, are postulated.
The “closed” variant exhibits stronger decrease of SMPS PCs, along the gas path, than in the open variant. This is due to the higher temperatures and concentrations in the closed system, which enable more intense agglomeration effects, thermophoresis- and diffusion losses.
The NP concentrations are always higher in the “open” variant.
The type of sampling: “open” or “closed”, as well as the sampling position in the exhaust installation, significantly influence the measured nanoparticle emissions.
The authors recommend NP tailpipe sampling with strong “atmospheric” dilution and the closed CVS system for gaseous emission components. That would be best suited solution for possible legislated measurement systems of the nanoaerosol from 2-stroke gasoline engines, with lost oil lubrication.