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To characterize the effects of renewable fuels on particulate emissions from GDI engines, engine experiments were conducted using EN228-compliant gasoline fuel blends containing no oxygenates, 10% ethanol (EtOH), or 22% ethyl tert-butyl ether (ETBE). The experiments were conducted in a single cylinder GDI engine using a 6-hole fuel injector operated at 200 bar injection pressure. Both PN in raw exhaust and solid PN (SPN) were measured at two load points and various start of injection (SOI) timings. Raw PN and SPN results were classified into various size ranges, corresponding to current and future legislations. At early SOI timings, where particulate formation is dominated by diffusion flames on the piston due to liquid film, the oxygenated blends yielded dramatically higher PN and SPN emissions than reference gasoline because of fuel effects.

This paper investigates how particulates number PN is influenced by fuel wall-film, liner wetting, and the mixing quality for different start of injection timings (SOI). Both experimental data with PN measurements, endoscope images from a high-speed camera from a single-cylinder engine, and CFD simulations were used for the analysis. Engine geometry was a spray-guided system with 300 bar fuel pressure and with single injections. Data was captured for 2000 rpm / 9 bar IMEPn. The results show that fuel film on the piston was only found to significantly increase PN for over-advanced SOI (in our engine geometry, earlier than -310 CAD). This results in luminescence from diffusion burn on the piston surface, which strongly contributes to PN. For an SOI timing of -310 CAD, fuel film on piston reaches a maximum of 3% of the injected fuel, vaporizes, and no remaining fuel film is found at the time of ignition. Approximately 0.5-1% of the fuel ends up on the liner.

Public health risk and resulting stringent emission regulations for internal combustion engines pose a need for solutions to reduce particle emissions (PN). Current PN control approaches include increasing fuel injection pressure, optimizing spray targeting, multiple injection strategies, and the use of tumble flaps together with gasoline particulate filters (GPF). Experiments were performed using a single-cylinder spark-ignited GDI engine equipped with a custom inlet manifold and a port fuel injector located 500 mm upstream. Particulate emissions were measured during stationary medium/high load operation to evaluate the effect of varying the mass split between the direct and upstream injectors. Mixing quality is improved substantially by upstream injection and can thus be controlled by altering the mass split between the injectors.

To assist efforts reducing harmful emissions from internal combustion engines, particulate formation was investigated in a compressed natural gas (CNG) Direct Injection single-cylinder SI engine in warm-up conditions. This involved tests at low engine speed and load, with selected engine coolant temperatures ranging from 15 to 90 °C, and use of a gasoline direct injection (GDI) system as a standard reference system. Total particulate number (PN), their size distribution, standard emissions, fuel consumption and rate of heat release were analyzed, and an endoscope with high-speed video imaging was used to observe combustion luminescence and soot formation-related phenomena. The results show that PN was strongly influenced by changes in coolant water temperature in both the CNG DI and GDI systems. However, the CNG DI engine generated 1 to 2 orders of magnitude lower PN than the GDI system at all tested temperatures.

Gasoline direct injection (GDI) engines usually emit higher levels of particulates in warm-up conditions of a driving cycle. Thus, sources of soot formation in these conditions were investigated by measuring particulate numbers (PN) emitted from a single-cylinder GDI engine and their sizes. The combustion was also visualized using an endoscope connected to a high-speed camera. Engine coolant and oil temperatures were varied between 15 and 90oC to mimic warm-up conditions. In addition, effects of delaying the start of ignition (SOI) on the emissions in these conditions were examined. Coolant and oil temperatures were varied individually to identify which factor has most effect on PN emissions. While coolant temperature strongly influenced PN with cold oil, the oil temperature insignificantly affected PN at low coolant temperature. These findings indicate that PN emissions are heavily dependent on the engine block’s temperature, which is dominated by the coolant.