Particle Number Emissions of Gasoline, Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) Fueled Vehicles at Different Ambient Temperatures

Compressed natural gas (CNG) and liquefied petroleum gas (LPG) are included in the group of promoted transport fuel alternatives for traditional fossil fuels in Europe. Both CNG and LPG fueled vehicles are believed to have low particle number and mass emissions. Here, we studied the solid particle number (SPN) emissions >4 nm, >10 nm and >23 nm of bi-fuel vehicles applying CNG, LPG and gasoline fuels in laboratory at 23 degrees C and sub-zero (-7 degrees C) ambient temperature conditions. The SPN23 emissions in CNG or LPG operation modality at 23 degrees C were below the regulated SPN23 limit of diesel and gasoline direct injection vehicles 6 x 10(11) 1/km. Nevertheless, the limit was exceeded at sub-zero temperatures, when sub-23 nm particles were included, or when gasoline was used as a fuel. The key message of this study is that gas-fueled vehicles produced particles mainly <23 nm and the current methodology might not be appropriate. However, only in a few cases absolute SPN >10 nm emission levels exceeded 6 x 10(11) 1/km when >23 nm levels were below 6 x 10(11) 1/km. Setting a limit of 1 x 10(11) 1/km for >10 nm particles would also limit most of the >4 nm SPN levels below 6 x 10(11) 1/km.