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The use of fuel blends like diesel/biodiesel, diesel/ethanol, and diesel/gasoline in internal combustion engines is spreading because it can reduce the engine pollutant emissions without significant hardware modifications. Moreover, it allows to fulfill the emission limits legislation. In this context, studies on the blends of diesel and propane fuels are poor in literature. Before using them in the engine, some preliminary investigations are necessary to know which are the effects of this mixed fuel in conventional injection systems. In this work, commercial diesel fuel and propane/diesel blends have been tested. In particular, two concentrations: 80% diesel and 20% propane, and 60% diesel and 40% propane have been prepared and stored in a pressurized tank. A conventional common rail injection system and a solenoid multi-hole injector have been used to deliver the fuel at high-pressure in a vessel at ambient temperature and pressure. Injection strategies in terms of energizing time and injection pressure have been taken from the functioning map of a real engine. Imaging measurements were focused on the near-nozzle field as the high volatility of the propane affects the spray behavior immediately after exiting from the injector nozzle. High-speed imaging has been performed using a long-distance microscopic objective and a synchronized flash-lamp. Measurements of the spray cone angle at the nozzle hole exit have been performed during the injection process. The tests showed that the propane/diesel blends have a wider angle than diesel. It is due to the high volatility of the propane more than on the injection pressure. To evaluate the effect of the operating condition and of propane concentration on the cone angle, the experimental results have been used to set-up an empirically derived correlation. It allowed to correlate the behavior of the cone angle of blended fuels to the case of pure diesel in the near-nozzle field.
