Emissions from a vehicle fitted to operate on either petrol or compressed natural gas

The purpose of this work was to evaluate the physical and chemical properties of emission products from a six-cylinder sedan car under a variety of operating conditions, before and after it has been converted to compressed natural gas (CNG) fuel. The specific focus of the measurements was on emission levels and characteristics of ultra fine particles and the emission levels together with the emissions of gaseous pollutants for a range of operating conditions before and up to 3 months after the vehicle was converted are presented and discussed in the paper. The investigations showed that converting a petrol operating vehicle to CNG has the potential of reducing some of the emissions and thus risks, while it does not appear to have an impact on others. In particular there was no statistically significant change in the emission of particles for the vehicle operating on petrol, before the conversion, compared to the emissions for the vehicle operating on CNG, after the conversion. There was a significant lowering of emissions of total polycyclic aromatic hydrocarbons and formaldehyde when the vehicle was operated on CNG, and a reduction of global warming potential was also observed when the vehicle was run on CNG, but the later gain is only at high vehicle speeds/loads, and would thus have to be considered in view of traffic and transport models for the region (in these models vehicle speed is an important parameter).