Experimental Investigation of Fuel Film Characteristics of Ethanol Impinging Spray at Ultra-Low Temperature

Increasing the injection pressure in DISI engine is an efficient way to obtain finer droplets but it will also potentially cause spray impingement on the cylinder wall and piston. Consequently, the fuel film sticking on the wall can dramatically increase the soot emission of the engine especially in a cold start condition. On the other hand, ethanol is widely used as an alternative fuel in DI engine due to its sustainable nature and high octane number. In this study, the fuel film characteristics of single-plume ethanol impinging spray was investigated. The experiments were performed under ultra-low fuel/plate temperature to simulate the cold start condition in cold areas. A low temperature thermostatic bath combined with specially designed heat exchangers were used to achieve ultra-low temperature for both the impinging plate and the fuel. Laser induced fluorescence (LIF) technique was employed to measure the thickness of fuel film deposited on the impinging plate. Rhodamine 6G was resolved into ethanol as the tracer, which can be excited by 532 nm laser and fluorescence at 560-590 nm. A low speed imaging system was used to capture the film characteristics. The LIF signal was converted to film thickness following a known height calibration approach. It was found that, with the decrease of plate temperature, the average film became thicker and the adhered mass increased although the wetted area became smaller due to the larger viscosity. Moreover, lower fuel temperature leads to thicker film and more adhered mass. The wetted areas are close to each other under different fuel temperatures.