Effect of injection pressure and ambient density on spray characteristics of diesel and biodiesel surrogate fuels

This paper presents novel experimental investigations on the influence of varying injection pressure and ambient density on evaporating sprays of diesel, tetradecane (as a diesel surrogate) and methyl oleate (as a biodiesel surrogate) fuels. Evidently, adapting high injection pressure and ambient density would remarkably enhance the atomization process, and in return improve the engine combustion, performance, and emission characteristics. Measurements were carried out in a rapid compression and expansion machine (RCEM) working under diesel engine-like conditions. Furthermore, a shadowgraph optical technique was applied, using a high-speed camera to capture the spray development at 20,000 frames per second (fps) to obtain the vapor penetration length, liquid penetration length and spray cone angle. The tested fuel was injected into a pressurized nitrogen gas in a diesel engine-like condition without combustion where the injection pressure and ambient density were varied from 50 MPa to 150 MPa, and from15 kg/m³ to 25 kg/m³, respectively. Results indicated that injection pressure and ambient density have a significant effect on the spray characteristics. Increasing the injection pressure from 50 MPa to 150 MPa results in the increase of vapor penetration by up to 33.2%, 21.5% and 24.4% for diesel, tetradecane and methyl oleate, respectively. Besides, increasing the ambient density from 15 kg/m³ to 25 kg/m³ results in a wider spray cone angle by up to 9.6%, 11.8% and 13.8%, for diesel, tetradecane and methyl oleate, respectively and a shorter vapor penetration by up to 9.2%, 11% and 13.1%, respectively. It is noticed that high injection pressure causes the least reduction in spray cone angle for biodiesel. The present measurements are considered bench-mark for validation of high-fidelity numerical simulation of diesel and biodiesel sprays.