Determination of Euro 6 LPG passenger car emission factors through laboratory and on-road tests: Effect on nation-wide emissions assessment for Italy

Abstract

Five Euro 6 LPG (liquefied petroleum gas) bi-fuel passenger cars well representative of the Italian circulating fleet were tested in laboratory (in repeatable conditions on a chassis dynamometer) and on road (in real traffic conditions using a portable emissions measurement system). The regulated and unregulated exhaust emissions and the energy consumptions measured with gasoline and LPG fuelling were compared. All the regulated emissions were compliant with the Euro 6 limits over the type-approval driving cycles and over the RDE (Real Driving Emissions) tests except for the particle number emission measured from the only direct injection engine tested car with gasoline fuelling, which exceeded the emission limit by 10.9% in laboratory and by 17.2% on road. Switching from gasoline to LPG fuelling, systematic carbon dioxide emission reductions were detected. Based on sub-cycles data, distance-specific exhaust emission factors and energy consumption factors were calculated for LPG fuelling and subsequently compared with those proposed by the EMEP/EEA (European Monitoring and Evaluation Programme/European Environment Agency) guidebook, which are integrated in the COPERT (COmputer Programme to calculate Emissions from Road Transport) model. The comparison showed a reasonable agreement for carbon monoxide and energy consumption for the medium segment, whereas more marked differences were found for the other compared emissions, with almost systematically lower values for the experimental factors. The comparison was then extended to the results of the national emissions calculation from Euro 6 LPG passenger cars in Italy, obtained using the EMEP/EEA factors and the experimental factors. These latter factors led to country-level lower emission estimates for all species, with the largest difference (around 90% less) for PM emission and smaller but still relevant (5%–23% range) differences for NOx, carbon monoxide, and total hydrocarbons. A considerable reduction (15.6%) was also found for the small segment with the new energy consumption factors, whereas a less marked reduction (1.8%) was found for the medium segment. The findings highlight the importance of up-to-date factors in order to obtain much more realistic and accurate estimations of exhaust emission and energy consumption within national inventories. • Emissions of five Euro 6 LPG bi-fuel cars were measured in laboratory and on road. • LPG tests showed reductions in CO 2 and particulate emissions vs. gasoline ones. • Emission factors for Euro 6 LPG bi-fuel cars were calculated from experimental data. • COPERT emission factors in most cases overestimate Euro 6 LPG emission values. • Overall emissions of Italian Euro 6 LPG fleet reduced by using experimental factors.