Particle emissions measurements on CNG vehicles focusing on Sub-23nm

Abstract

The current study investigates the nonvolatile particle number emissions of three bi-fuel passenger cars (Euro 6 b , 6 d-temp), which operate on compressed natural gas (CNG), as a primary fuel, and gasoline as a secondary one. The CNG fuel was injected into the engine using port fuel injection (PFI) while the gasoline fuel was either by PFI or by direct injection (GDI). A novel exhaust gas sampling and dilution system was employed for the determination of solid particle number (SPN) emissions at 10 nm (SPN >10nm) and 2.5 nm (SPN >2.5 nm). The vehicles were tested in the laboratory over different test cycles where the CNG solid particle number emissions greater than 23 nm (SPN >23nm) were an order of magnitude lower than GDI and PFI gasoline emissions. However, when the size threshold was lowered to 10 nm or 2.5 nm, emissions were similar for both fuels. Particularly, SPN >2.5 nm emissions of the Euro 6 b vehicle exceeded the Euro 6 emission standard for both fuels while the SPN >23nm emissions were between 40 and 2.8 times lower than the limit for CNG and gasoline, respectively. Particle size distributions show a significant number of particles reside below the regulated limit of 23 nm, even lower than 10 nm. The results have significant implications in setting a particle number limit for alternative fuel vehicles while indicating that the current size threshold (23 nm) is insufficient for particle emission testing.

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

“…The vehicles appeared as low SPN emitters only when SPN23 in 23 • C testing conditions in gaseous fuel operation modality was considered. In agreement with our results, in the literature, 23 • C test SPN23 emissions of CNG and LPG fuelled PFI vehicles over various test cycles are repeatedly shown to be below the direct injection vehicle SPN-limit of 6 × 10 11 1/km [10][11][12][13]45,51].…”

“…The CNG and LPG fueled vehicles are connected to low particle emissions when particulate matter (PM) mass or solid particle number (SPN) in a >23 nm size range (SPN23) is considered [9][10][11][12][13][14][15]. In fact, as most of the CNG and LPG fueled vehicles in European market apply port fuel injection or multiport fuel injection (PFI) [16], their particle emissions are not regulated in Europe.…”

“…In the European Union's regulation, PM mass and SPN23 limits are set only for vehicles applying direct fuel injection (DI) and, thus, in practice, are set for compression ignited diesel vehicles and spark ignited direct injection gasoline (GDI) vehicles [17]. Along with the regulation and the related advances in emission control, SPN for DI vehicles have decreased and gasoline PFI vehicles may nowadays appear as a high SPN23 emitters [18] In addition, notable particle number emissions in <23 nm size range (sub-23 nm) are detected for PFI vehicles [13,[18][19][20][21]. The CNG fueled vehicles' SPN in size range from 10 nm to 23 nm and even below 10 nm is shown exceed the emissions of the gasoline and diesel fueled vehicles [13,[22][23][24][25].…”

“…Along with the regulation and the related advances in emission control, SPN for DI vehicles have decreased and gasoline PFI vehicles may nowadays appear as a high SPN23 emitters [18] In addition, notable particle number emissions in <23 nm size range (sub-23 nm) are detected for PFI vehicles [13,[18][19][20][21]. The CNG fueled vehicles' SPN in size range from 10 nm to 23 nm and even below 10 nm is shown exceed the emissions of the gasoline and diesel fueled vehicles [13,[22][23][24][25].…”

“…As mentioned above, the low exhaust emissions of CNG and LPG fueled vehicles are often used to promote the fuels in transportation use. In practical terms, however, the light-duty CNG and LPG fueled vehicles sold in European market apply mostly gasoline as a second or reserve fuel and the emissions of the vehicles in gasoline operation modality may have a notable impact on the emission levels of the vehicles [10][11][12][13][14][15][16]45]. Thus, when it comes to estimation of bi-fuel vehicle particle emissions, also gasoline operation should be considered as gasoline SPN emissions are usually higher than the emissions in gaseous fuel operation.…”