Characterization of diesel spray with novel high-speed laser absorption scattering technique under diesel engine-like condition

Abstract

In Diesel Engines, the injection process plays a decisive role in the combustion efficiency. Hence, the characterization of diesel sprays is very important. Several methods are developed, however, none of them records the temporal fuel distribution throughout the individual injection event and measures the liquid/vapor concentration of an evaporating diesel spray. In this work, two light sources i.e., an ultraviolet LED and a continuous wave laser, were used with two high-speed video cameras. A fuel mixture with the compositions of 97.5 % n-tridecane and 2.5 % of volume-based 1-methylnaphthalene was selected as the test fuel. The fuel was intermittently injected into an inert environment at 4.8 MPa and 800 K by applying a seven-hole injector with a hole diameter of 0.123 mm. The injection pressure was set at 100 MPa and the injection amounts were set as 2.5 and 5.0 mg/hole to observe the effect of the injected mass on the spray characteristics and mixture formation process. Calibration, based on the scattering by non-evaporating sprays and molar absorption coefficients for fully evaporated sprays, indicates a measurement error of 15 %. The findings of the experiments show that, under large injection mass conditions, the liquid phase equivalence ratio is quite low and close to zero just after the end of injection which points out that as the air-fuel mixing quality improves, the majority of the liquid fuel is rapidly converted to vapor. The air-fuel mixture is overall richer at large injected mass compared to the small mass condition. Furthermore, after the end of injection, the high fuel vapor concentration area near the nozzle soon mixes with ambient gas, decreasing the equivalence ratio to low levels, whereas a high-vapor-concentration region is still present at the spray head. This study provides a valuable insights into the behavior of the fuel spray, which could be used to improve the efficiency and performance of diesel engines.