A path toward a new generation of sustainable spark ignition engines: Experimental investigations on the synergic use of dual diluted combustion and renewable fuels

Nowadays, the most effective way to tackle the urgent demand for sustainable mobility is the fast development of a wide portfolio of powertrain solutions featuring a low carbon footprint. The PHOENICE (PHev towards zerO EmissioNs & ultimate ICE efficiency) H2020 project aims to demonstrate that highly efficient, low-emitting Internal Combustion Engines (ICEs) remain a viable solution to reduce the environmental impact of road vehicles. This paper presents the results of an extensive experimental campaign on the PHOENICE engine concept which exploits the synergistic combination of homogeneous lean combustion, Exhaust Gas Recirculation (EGR), high compression ratio and aggressive cycle Millerization. The study details the sensitivities on fuel injection, intake valve timing and combustion dilution to assess their impact on fuel conversion efficiency and engine-out emissions. The engine was tested in three combustion modes, achieving a peak Brake Thermal Efficiency (BTE) of 38 % and a broad operating range above 34 % under stoichiometric conditions. EGR provided a maximum relative efficiency gain of 4.2 %, while the combination of EGR and lean combustion yielded to an additional 4.6 % gain with a peak Indicated Thermal Efficiency (ITE) of 47 %. Compared to the baseline engine, the PHOENICE concept reduced Brake Specific Fuel Consumption (BSFC) by at least 10 % over a substantial portion of the engine map. Furthermore, this study explored the fuel economy potential of E85, a renewable blend containing 85 % bioethanol and 15 % gasoline. Results showed up to a 16 % reduction in BSFC in the low-end torque region, largely due to the fuel high knock resistance.