Regulated and Unregulated Exhaust Emissions from CNG Fueled Vehicles in Light of Euro 6 Regulations and the New WLTP/GTR 15 Test Procedure

The aim of this paper was to explore the influence of CNG fuel on emissions from light-duty vehicles in the context of the new Euro 6 emissions requirements and to compare exhaust emissions of the vehicles fueled with CNG and with gasoline. Emissions testing was performed on a chassis dynamometer according to the current EU legislative test method, over the New European Driving Cycle (NEDC). Additional tests were also performed on one of the test vehicles over the World Harmonized Light Vehicles Test Cycle (WLTC) according to the Global Technical Regulation No. 15 test procedure. The focus was on regulated exhaust emissions; both legislative (CVS-bag) and modal (continuous) analyses of the following gases were performed: CO (carbon mono_xide), THC (total hydrocarbons), CH₄ (methane), NMHC (non-methane hydrocarbons), NO_x (oxides of nitrogen) and CO₂ (carbon dioxide). Furthermore, unregulated exhaust emissions were also examined in certain cases: particle number and mass, as well as emissions of NH₃ (ammonia), NO (nitrogen mono_xide) and NO₂ (nitrogen dioxide). The results showed a range of differences in terms of regulated emissions, particulate matter and ammonia emissions, and also in the composition of the NO_x in the exhaust gas (i.e. the NO:NO₂ ratio). Emissions of both CO₂ and particulates were markedly lower when running on CNG. Emissions from the two phases of the NEDC and the four phases of the WLTC were briefly analysed.