Analysis of Back Pressure Variation on Macroscopics Characteristics of Ethanol E100 Spray

The growing demand for more efficient and less polluting engines has lead the scientific community to further develop the road map engine technologies, including direct fuel injection. Direct injection research demands the investigation of spray formation and its characteristics. The present work performs the characterization of the macroscopic parameters of ethanol sprays (E100) produced with a fuel gauge pressure of 80 bar and gauge back pressures of 0, 5 and 10 bar. The sprays analysis was performed using high speed filming by means of Shadowgraph technique. Computational routines of matrix analysis were applied to measure the spray cone angles, penetration and penetration rate. The spray visualization demanded an experimental apparatus composed of a pressurized cylinder with nitrogen, a fuel tank as pressure vessel, an injection driver equipped with a peak and hold module controlled by a MoteC M84, a Phantom V7.3 high speed camera and LEDs for illumination. The filming rate was 8000 frames per second. The cone angle determination was done through an automated Matlab image processing routine. The cone angle calculus methodology is presented in the manuscript. A study of the spray penetration as a function of time is also accomplished. The results obtained were coherent, the fitted curves presented a remarkable Pearson coefficient, suggesting a high degree of reliability. Some unexpected phenomena were observed, such as higher spray speeds with 10 bar back pressure than 5 and spray narrowing. Hypotheses were raised to explain such phenomena.