Among the technical solutions that can lead to energy converters with high thermal efficiency, the direct injection diesel (DID) engine ranks in a good position. This technology, once used only for heavy duty and stationary engines, is now spreading and reaches private cars, thanks to the developments of electronic control and injection equipments (high-pressure pump, 2 springs injectors, etc.), which improved the combustion control and the trade-off in terms of NOx and particulate matter (PM) emissions and in terms of noise. Recent vehicles are equipped with EGR and oxidation catalyst, making the tuning of the engine even more complex. Then, to take the best advantage from this technology, it becomes a major concern to assess precisely the sensitivity of direct injection diesel engines to fuel characteristics.
With a set of fuels formulated to cover large ranges of chemical compositions, viscosities, cetane numbers and densities, a private car, powered by a modern 4 cylinders, 1.9 liter DI engine, was run at the chassis dynamometer and a corresponding engine was run at the test bench. The impact of the fuel characteristics on regulated or unregulated (PAH, aldehydes) pollutant emissions and on the noise level was assessed either in standard tuning conditions, or while varying the EGR rate or the injection timing.
For chassis dynamometer tests, the new MVEG* cycle was selected, while for test bench studies three operating points were retained as representative of the partial load engine running.
In both cases, the results show that the cetane number has a strong influence on CO and HC emissions and on the particulates IOF / SOF ratio. An effect of the fuel density, more important on transient conditions, is observed on CO, particulates, SOF and aldehydes emissions.
The chemical composition, and particularly the aromatic content, had no clear impact on the gaseous emissions (CO and HC) in steady state conditions (tests on engine). Whereas, on transient mode (tests on vehicle), an influence is also detected on particulate and SOF levels. On the opposite, NOx emissions seem to present a low sensitivity to fuel characteristics.
The study reported in this communication has been conducted within the program of the “Groupement Moteur Carburant Lubrifiant (GMCL)”, in collaboration with ELF, OCTEL, PEUGEOT CITROËN, RENAULT and TOTAL.