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The objective of the paper is to characterize the diesel spray under the ambient conditions relevant for direct injection (D.I.) diesel engines. The particular emphasis is on the comparisons between laser measurements and predictions by empirical correlations and theoretical analyses. The ultraviolet-visible laser absorption-scattering (LAS) imaging technique is employed to quantitively determine the spray/mixture properties of the diesel spray injected by a hole-type injector, in terms of spray tip penetration and spatial concentration distributions of liquid and vapor phase. The structure of evaporating spray is obtained and analyzed. Based on the penetration correlations in the literature, a non-dimensional analysis of the spray tip penetration data is carried out. The results indicate that a self-similar state of the evaporating fuel spray is achieved.

Three-Dimensional visualization technique based on volume rendering method has been developed in order to translate a calculated result of diesel combustion simulation into an realistically spray and flame image. This paper presents an overview of diesel combustion model which has been developed at Hiroshima University, a description of the three-dimensional visualization technique, and some examples of spray and flame image generated by this visualization technique.

The group-hole (GH) nozzle concept that uses two closely spaced micro-orifices to substitute the conventional single orifice has the potential to facilitate better fuel atomization and evaporation, consequently attenuate the soot emission formed in direct-injection (D.I.) diesel engines. Studies of quantitative mixture properties of the transient fuel spray injected by the group-hole nozzles were conducted in a constant volume chamber via the laser absorption-scattering (LAS) technique, in comparison with conventional single-hole nozzles. Specific areas investigated involved: the non-evaporating and the evaporating ambient conditions, the free spray and the spray impinging on a flat wall conditions. The particular emphasis was on the effect of one of key parameters, the interval between orifices, of the group-hole (SH) nozzle structure.

An experimental and numerical study was conducted on the spray and mixture properties of a hole-type injector for direct injection (D. I.) gasoline engines. The Laser Absorption Scattering (LAS) technique was adopted to simultaneously measure the spatial concentration distributions and the mass of the liquid and vapor phases in the fuel spray injected into a high-pressure and high-temperature constant volume vessel. The experimental results were compared to the numerical calculation results using three-dimensional CFD and the multi-objective optimization. In the numerical simulation, the design variable of the spray model was optimized by choosing spray tip penetration, and mass of liquid and vapor phases as objective functions.

In the present study, a challenge has been made to quantitatively determine the vapor phase concentration distributions in an evaporating multicomponent fuel spray using the LAS imaging technique. The theoretical considerations were particularly given when applying the LAS imaging technique to the multicomponent fuel spray and reconstructing the vapor concentration distributions from the spray images.

Experimental and computational studies were carried out to characterize the spray development and evaporation processes of multi-hole injector for direct injection spark ignition (DISI) engines. The main injector parameter to be investigated in this study is a diverging angle between neighboring two holes. In the experimental study, the influence of the diverging angle on evaporation process of fuel spray from two-hole injector was investigated using Laser Absorption Scattering (LAS) measurement. Smaller diverging angle causes larger spray tip penetration because the momentum of the spray from one hole emphasizes another, when two spray merge to one. Moreover, spray tip penetration decreases at certain diverging angle due to the negative pressure region between two sprays. Mechanisms behind the above spray behaviors were discussed using the detailed information on the spray and ambient gas flow fields obtained by the three dimensional computational fluid dynamics (CFD).

In order to investigate the effect of split injections on mixture formation processes in Direct Injection (DI) gasoline engine sprays, an experimental study was conducted applying the laser absorption and scattering (LAS) technique to the sprays using double pulse injections with various dwells and mass ratios. The effects of various dwells and mass ratios between the pulsed injections on the spatial concentration distributions in the spray, the penetration of vapor and liquid phases, and the mean equivalence ratios of the vapor phase and overall spray, were clarified. It was found that the phenomenon of high concentration liquid spray piling up at the leading edge of the spray is avoided by the double injections with enough dwell or appropriate mass ratio. The maximum penetration length of the spray significantly decreases, especially for the liquid phase with high concentration.

The breakup and atomization processes of the pre-swirl spray, which is produced before the hollow-cone spray from a high-pressure swirl-type D.I. gasoline injector, were investigated under different ambient pressure conditions. The injector has a press-fitted swirl tip, in which six tangential slots giving the injecting fuel an angular momentum are perforated at an equal space interval. A microscopic imaging technique was applied to get the spatially high-resolution LIF tomograms of the pre-swirl spray. The sprays were illuminated by an Nd:YAG laser light sheet and imaged using a high resolution CCD camera, fixed with a micro lens and coupled with an optical low-pass filter. The droplet size and the individual droplet's velocity were obtained by applying the image processing and the particle tracking techniques, respectively.

Reduction of orifice diameter of nozzle is advantageous to the fuel atomization in a D.I. diesel engine. However, the diameter reduction is usually accompanied with decrease of spray tip penetration, thus worsening fuel spatial-distribution and fuel-air mixing. In this paper, a group-hole nozzle concept was proposed to solve the problem resulting from minimization of orifice diameter. Compared to the conventional multi-hole nozzle, group-hole nozzle has a series group of orifices, and each group consists of two micro-orifices with a small spatial interval and small angle. For examining the characteristics of the spray injected by the group-hole nozzle, the ultraviolet-visible laser absorption-scattering (LAS) imaging technique was adopted to determine vapor concentration and droplets density as well as other spray characteristics such as spray angle and penetration of both vapor and liquid phases.

To get quantitative measurements of liquid and vapor phase concentration distributions in a gasoline spray, a laser-based absorption and scattering (LAS) technique was developed. The LAS technique adopts ultraviolet and visible lasers as light sources and a test fuel, which absorbs the ultraviolet light but does not absorb the visible light, instead of gasoline. The LAS principle is based on the incident light extinction in the ultraviolet band due to both vapor absorption and droplets scattering, whereas in the visible band, the incident light extinction is due only to the droplet scattering. The absorption spectra and molar absorption coefficients of the candidate test fuels including p-xylene, benzene and toluene, all of which have physical properties similar to gasoline, were investigated, and p-xylene was finally selected as a test fuel. Measurement accuracy of the LAS technique was discussed.

Experimental results of a diesel engine have shown that using split-injection can reduce the NOx and particulate emissions. For understanding the mechanism of emissions reduction, mixture formation in split-injection diesel sprays was characterized in the present paper. A dual-wavelength laser absorption-scattering (LAS) technique was developed by use of the second harmonic (532nm) and the fourth harmonic (266nm) of a pulsed Nd:YAG laser as the incident light and dimethylnaphthalene (DMN) as the test fuel. By applying this technique, imaging was made of DMN sprays injected into a high-temperature and high-pressure constant volume vessel by a single-hole nozzle incorporated in a common rail injection system for D.I. diesel engine. The line-of-sight optical thickness of both fuel vapor and droplets in the sprays was yielded from the sprays images.

Three-dimensional behaviors of direct injection (D.I.) gasoline sprays were investigated using 2-D and 3-D particle image velocimetry (PIV) techniques. The fuel was injected with a swirl type injector for D.I. gasoline engines into a constant volume chamber in which ambient pressure was varied from 0.1 to 0.4 MPa at room temperature. The spray was illuminated by a laser light sheet generated by a double-pulsed Nd:YAG laser (wave length: 532 nm) and the succeeding two tomograms of the spray were taken by a high-resolution CCD camera. The 2-D and 3-D velocity distributions of the droplet cloud in the spray were calculated from these tomograms by using the PIV technique. The effects of the swirl groove flows in the injector and the ambient pressure on the structural behavior of the droplet cloud in the spray were also examined.

Effects of split injection, with a relatively short time interval between the two sprays, on the spray development process, and the air entrainment into the spray, were investigated by using laser induced fluorescence and particle image velocimetry (LIF-PIV) techniques. The velocities of the spray and the ambient air were measured. The cumulative mass of the ambient air entrained into the spray was calculated by using the entrainment velocity normal to the spray boundary. The vortex structure of the spray, formed around the leading edge of the spray, showed a true rotating flow motion at low ambient pressures of 0.1 MPa, whereas at 0.4 MPa, it was not a true rotating flow, but a phenomenon of the small droplets separating from the leading edge of the spray and falling behind, due to air resistance. The development processes of the 2nd spray were considerably different from that of the 1st spray because the 2nd spray was injected into the flow fields formed by the 1st spray.

Measurements of the droplet and ambient air velocities in and around a D.I. gasoline spray were made by combining the laser induced fluorescence (LIF) and the particle image velocimetry (PIV) techniques. Before the fuel spray was injected into a constant volume vessel, rhodamine B-water solution was injected into the ambient air by a swirl-type injector for dispersing the fine fluorescent liquid particles as tracers for the ambient air motion. The fuel spray was injected into the fluorescent tracer clouds by a D.I. gasoline injector and was illuminated by an Nd:YAG laser light sheet (wave length: 532 nm). The light scattered by the droplets in the fuel spray was the same as the Nd:YAG laser wavelength, whereas the light emitted by the fluorescent tracer clouds was at a longer wavelength.

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.

An early formation process of the spray, which was injected by a high-pressure swirl-type injector that is widely used in direct injection spark ignition (DISI) gasoline engines, was investigated through image analyzing techniques. The sprays were illuminated both by an Nd:YAG laser light sheet for getting the spray tomograms and by a tungsten lamp for getting the scattered back light shadow images of the sprays. The sprays were imaged by using a high-resolution CCD camera and a high-speed digital imaging system. The early development aspects of the spray were investigated in detail through the measurement of the tip penetration, cone angle and width of the early spray. At the start of injection, the liquid column emerges first, and it forms the “pre-swirl spray” without the swirl component. Following the liquid column, the liquid sheet emerges, however its radial velocity component is weak to form the complete hollow-cone spray. This spray changes into the “weak-swirl spray”.

Spray penetration for Diesel injectors, where injection pressure varies with time during the injection period, was calculated. In order to carry out this calculation, the discharge coefficients of the needle-seat opening passage and discharge hole in orifice-type Diesel nozzles were investigated separately. Simple empirical correlations were obtained between these coefficients and needle lift. Then, by introducing these correlations, the injection pressure, which is defined as the pressure in the sac chamber just upstream of the discharge hole, was either derived from measured fuel supply line pressure, or predicted by means of an injection system simulation. Finally, based on the transient injection pressure, spray tip penetration was calculated by taking the overall line which covers the trajectories of all fuel elements ejected during the injection period.

The performance of a diesel engine largely depends on the spray behavior and mixture formation. Nozzle configurations and operating conditions are important factors that influence spray development. Using numerical and experimental methods, this study focused on the spray development of multi-hole nozzles under non-evaporating and evaporating conditions to compare the influence of nozzle hole diameter and injection pressure on spray characteristics. High-speed video observation was employed to study the properties of spray development under the non-evaporating condition, while the Laser Absorption Scattering technique was used in the observation and quantitative analysis of evaporating spray characteristics in the evaporating condition. In addition, computational fluid dynamics study results published previously [1] were correlated with the current experimental results to provide more detailed explanations about the mechanism of the characteristics of spray behavior.

With the aim of improving engine performance, recent trend of fuel injection nozzle design followed by engineers and researchers is focusing on more efficient fuel break up, atomization, and fuel evaporation. Therefore, it is crucial to characterize the effect of nozzle geometric design on fuel internal flow dynamics and the consequent fuel-air mixture properties. In this study, the internal flow and spray characteristics generated by the practical multi-hole (10 holes) nozzles with different nozzle hole length and hole diameter were investigated in conjunction with a series of computational and experimental methods. Specifically, the Computational Fluid Dynamics (CFD) commercial code was used to predict the internal flow variation inside different nozzle configurations, and the high-speed video observation method was applied to visualize the spray evolution processes under non-evaporating conditions.

A phenomenological spray-combustion model of a D.I. Diesel engine was applied to study the engine parameters with potential for reducing NOx and smoke emissions. The spray-combustion model, first developed at the University of Hiroshima in 1976, has been sophisticated by incorporating new knowledge of diesel combustion. The model was verified using data from an experimental, single cylinder, D.I. diesel engine with a bore of 135mm and a stroke of 130mm. After the verification process, calculations were made under a wide range of the engine parameters, such as intake air temperature, intake air pressure, intake swirl ratio, nozzle hole diameter, injection pressure, air entrainment rate into the spray, and injection rate profile. These calculations estimated the effects of the engine parameters on NOx, smoke and specific fuel consumption. As a result of the calculations, an approach for the low NOx and smoke emission engine was found.