Particulate Matter (PM) Emissions of Euro 5 and Euro 6 Vehicles Using Systems with Evaporation Tube or Catalytic Stripper and 23 nm or 10 nm Counters

Particle number (PN) emission limits were introduced in the European Union’s regulations for light-duty and heavy duty vehicles in the years 2011-2014. Since then, PN measurements have become a common practice in the automotive sector. Many studies showed that the current methodology, which counts particles >23 nm, misses a large fraction of particles for some engine technologies, such as port fuel injection vehicles or vehicles fueled with compressed natural gas (CNG). However, data for the latest technology vehicles are lacking. For this reason, we measured PN emissions >23 nm and >10 nm of >30 CNG, gasoline and diesel-fueled vehicles. Two systems were measuring in parallel from the full dilution tunnel; one with an evaporation tube and the other with a catalytic stripper. The PN emission levels spanned over three orders of magnitude depending on whether there was a particulate filter installed or not. The differences between the two systems (>23 nm) were on average 6%, indicating that a catalytic stripper could justifiably be permitted in future PN regulations. The ratio of 10-23 nm particles to >23 nm particles ranged from negligible up to many times higher. In many cases, sub-23 nm particles were emitted during cold start. During some high speed events, solid sub-23 nm particles were measured, but they were attributed to release of solid particles from the silicone adaptors. All particulate matter (PM) mass emissions were lower than 4.5 mg/km and <2 mg/km for vehicles equipped with particulate filters. There was no apparent correlation between PM mass and PN >23 nm or >10 nm.