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The objective of this study is to investigate the mixture formation process of sprays injected from two-hole nozzles for direct-injection spark-ignition (DISI) engines. Spray characteristics were examined for vapor and liquid mass distributions, spray tip penetration and spray angle using the laser absorption–scattering (LAS) technique and the computational fluid dynamics (CFD) simulation. Other characteristics including: the vapor phase concentration distribution, droplet spatial distribution and pressure distribution were acquired from the CFD simulation results. Comparison of measured and calculated results showed that as the hole-axis-angle (HAA) of the two-hole nozzle decreased, the droplet coalescence increased and vapor mass decreased. The spray with the HAA of 10° had the longest spray tip penetration and the spray with the HAA of 15° had the shortest one. The two jets of the two-hole nozzle spray had a tendency of offsetting to the central region of the spray. From 10 to 15 MPa, the increase in the injection pressure increased the vaporization rate and the spray tip penetration rate very much, but no such tendency was found when the injection pressure increased from 15 to 20 MPa.

An evaporation process plays an important role on the combustion and emission formation processes in a direct injection (D. I.) gasoline engines. An experimental study was conducted on the evaporation process of the non-axisymmetric wall-impinging spray injected by the hole type injector for a D. I. gasoline engine. For the quantitative measurement of the vapor of the non-axisymmetric spray, the image processing technique using the Laser Absorption Scattering (LAS) principle was newly developed. The total amount of fuel vapor in the whole spray was obtained from the optical thickness image of the vapor and the Lambert Beer's law. The amount of fuel vapor in the wall-impinging spray is decreased compared with the free spray. In addition, the amount of fuel vapor is decreased as the distance between nozzle tip and the impingement wall is decreased.

Ambient air velocity distributions in and around a D. I. gasoline spray were measured using a combination of LIF and PIV techniques. A rhodamine and water solution was injected into ambient air to disperse the fine fluorescent liquid particles used as tracers. A fuel spray was injected into the fluorescent tracer cloud and was illuminated by an Nd: YAG laser light sheet (532nm). The scattered light from the spray droplets and tracers was cut off by a high-pass filter (>560nm). As the fluorescence (>600nm) was transmitted through the high-pass filter, the tracer images were captured using a CCD camera and the ambient air velocity distribution could be obtained by PIV based on the images. This technique was applied to a D. I. gasoline spray. The ambient air flowed up around the spray and entered into the tail of the spray. Furthermore, the relative velocity between the spray and ambient air was investigated.

Mixture formation processes play a vital role on the performance of a D.I. Gasoline engine. Quantitative measurement of liquid and vapor phase concentration distribution in a D.I. gasoline spray is very important in understanding the mixture formation processes. In this paper, an unique laser absorption scattering (LAS) technique was employed to investigate the mixture formation processes of a fuel spray injected by a D.I. gasoline injector into a high pressure and temperature constant volume vessel. P-xylene, which is quite suitable for the application of the LAS technique, was selected as the test fuel. The temporal variations of the concentration distribution of both the liquid and vapor phases in the spray were quantitatively clarified. Then the effects of injection pressure and quantity on the concentration distributions of both the liquid and vapor phases in the spray were analyzed.