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.

The objective of this study is the assessment of the real-world environmental performance, and its comparison with laboratory measurements, of two Euro 6 passenger cars. The first is equipped with a common-rail diesel engine, Lean NO x Trap (LNT), and Diesel Particulate Filter (DPF), and the second is a bi-fuel gasoline/CNG (Compressed Natural Gas) vehicle equipped with a Three-Way Catalyst (TWC). The experimental campaign consisted of on-road and chassis dynamometer measurements. In the former test set, two driving routes were followed, one complying with Real Driving Emissions (RDE) regulation and another characterized by more dynamic driving. The aim of the latter route was to go beyond the regulatory limits and cover a wider range of real-world conditions and engine operating areas. In the laboratory, the WLTC (Worldwide harmonized Light vehicles Test Cycle) was used, applying the real-world road load of the vehicles. Both cars underwent the same tests, and these were repeated for the primary (CNG) and the secondary (gasoline) fuel of the bi-fuel vehicle. In all of the tests, CO 2 and NO x emissions were measured with a Portable Emissions Measurement System (PEMS). The results were analyzed on two levels, the aggregated and the instantaneous, in order to highlight the different emissions attributes under varying driving conditions. The application of realistic road load in the WLTC limited its difference from the RDE-compliant route in terms of CO 2 emissions. However, the aggressive driver behavior and the uphill roads of the Dynamic driving schedule resulted in approximately double the CO 2 emissions for both cars. The potential of natural gas to reduce CO 2 emissions was also highlighted. Concerning the NO x emissions of the diesel car, the real-world results were significantly higher than the respective WLTC levels. On the other hand, the bi-fuel car exhibited very low NO x emissions with both fuels. Natural gas resulted in increased NO x emissions compared to gasoline, always remaining below the Euro 6 limit, with the only exception being the Dynamic driving schedule. Finally, it was found that the overall cycle dynamics are not sufficient for the complete assessment of transient emissions, and the instantaneous engine, and aftertreatment behavior can reveal additional details.

Vehicles’ powertrain electrification is one of the key measures adopted by manufacturers in order to develop low emissions vehicles and reduce the CO2 emissions from passenger cars. High complexity of electrified powertrains increases the demand of cost-effective tools that can be used during the design of such powertrain architectures. Objective of the study is the proposal of a series of real-world velocity profiles that can be used during virtual design. To that aim, using three state of the art plug-in hybrid vehicles, a combined experimental, and simulation approach is followed to derive generic real-world cycles that can be used for the evaluation of the overall energy efficiency of electrified powertrains. The vehicles were tested under standard real driving emissions routes, real-world routes with reversed order (compared to a standard real driving emissions route) of urban, rural, motorway, and routes with high slope variation. To enhance the experimental activities, additional virtual mission profiles simulated using vehicle simulation models. Outcome of the study consists of specific driving cycles, designed based on standard real-world route, and a methodology for real-world data analysis and evaluation, along with the results from the assessment of the impact of different operational parameters on the total electrified powertrain.

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