Fuel consumption and exhaust emissions from Euro 6d vehicles fueled by innovative LPG/DME blend

The aim of this research was to investigate the exhaust emissions from vehicles when fueled by a new and fully renewable fuel if made of bio-LPG and renewable dimethyl ether (DME), in comparison with standard gasoline. For this purpose, DME was mixed with liquefied petroleum gas (LPG) and used to fuel three bi-fuel LPG/gasoline spark-ignition engines light-duty vehicles. The suitable fuel blend was selected based on several octane tests using CFR engines. Exhaust emissions were tested over the WLTC and over the hot-start CADC cycles, as well as on the road. All Euro 6 standards were well fully met over the WLTC with both fuels. Switching from gasoline to LPG/DME fueling, the CO and NOx emission factors increased for two vehicles, whereas THC and NMHC decreased. Regarding particulates, for two vehicles the emission factors decreased, too. Generally, when the vehicles were driven on the CADC, lower gaseous emissions were observed compared to WLTC: excluding one vehicle, when switching from gasoline to LPG/DME fueling, the overall emission profiles reflected those of the same vehicles run on the WLTC. The unregulated particulate emissions measured over both testing cycles reflect what was detected for the regulated ones. Except for PN10, which was not measured, all regulated emissions were found to meet the (most severe) Euro 7 standards proposed at first by the European Commission. RDE tests showed that all vehicle emissions obtained from on-road tests were also found to meet the RDE standards, regardless of the fueling. Concerning CO₂ emissions, LPG/DME fueling guaranteed a systematic decrease for all vehicles and cycles, both on road and in the laboratory. The present investigation aims at demonstrating that the innovative LPG/DME 80 %/20 % (m/m) blend not only can be deemed as potentially suitable for GHG emissions reduction, as long as both DME and propane are obtained from renewable sources, but even compliant with EN 589 and both Euro 6 and part of preliminary Euro 7 exhaust emission proposal.