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To reduce carbon dioxide emission and to relieve the demand of fossil fuels, ethanol is regarded as one of the most promising alternative fuels for gasoline. Recently, using ethanol in the state-of-the-art gasoline engine, direct-injection spark-ignition (DISI) engine, has become more attention by researchers due to less knowledge of the ignition and combustion processes in that engine. In this study, different ethanol-gasoline blended fuels, E0 (100% gasoline), E85 (85% ethanol and 15% gasoline mixed in volume basis) and E100 (100% ethanol) were injected by a valve-covered-orifice (VCO) hole-type nozzle. The experimental environment was set to the condition similar with the near top dead center (TDC) in DISI engine. The high-speed imaging of shadowgraph, OH* chemiluminescence and flame natural luminosity were used to clarify the characteristics of the ignition process, flame development and propagation.

Spray characteristics under very small injection amount injected by the hole-type nozzle for a D.I. Diesel engine were investigated using the spray test rig consisting a high-pressure and high-temperature constant volume vessel with optical accesses and a common rail injection system. The Laser Absorption Scattering (LAS) technique was used to visualize the liquid and vapor phase distributions in the evaporating spray. In the very small injection amount condition of the evaporating and free (no wall impingement) spray, the both spray tip penetration and spray angle are larger than those of the non-evaporating free spray. This tendency contradicts the previous observation of the diesel spray with large injection amount and the quasi steady state momentum theory. In the case of the spray impinging on a 2-dimensional piston cavity wall, the spray tip penetration of the evaporating spray is larger than that of the non-evaporating spray.

The effect of spray/wall interaction on diesel spray flame characteristics was investigated by applying LAS (Laser Absorption-Scattering) technique, OH* chemiluminescence and two color pyrometry in a constant volume vessel. To insure the precision of this investigation, following necessary verification experiments were carried out: (1) OH* chemiluminescence and two color pyrometry were synchronously employed to analyze the influence of soot incandescence on OH* chemiluminescence signal intensity; and (2) frontal view and side view OH* images of a linearly arranged three holes injector were concentrated on to investigate the effect of soot on optical intensity attenuation under line-of-sight image recording condition. And then the effect of impinging distance (30,40,50,60 mm and free) on diesel spray and combustion behaviors were studied. The results reveal that the impinging distance plays a significant role in mixture formation.

Spray combustion processes of palm oil biodiesel (PO) and conventional diesel fuels were simulated using the CONVERGE CFD code. Thermochemical and reaction kinetic data (115 species and 460 reactions) by Luo et al. (2012) and Lu et al. (2009) (68 species and 283 reactions) were implemented in the CONVERGE CFD to simulate the spray and combustion processes of the two fuels. Tetradecane (C14H30) and n- heptane (C7H16) were used as surrogates for diesel. For the palm biodiesel, the mixture of methyl decanoate (C11H20O2), methyl-9-decenoate (C11H19O2) and n-heptane was used as surrogate. The palm biodiesel surrogates were combined in proportions based on the previous GC-MS results for the five major biodiesel components namely methyl palmitate, methyl stearate, methyl oleate, methyl linoleate and methyl linolenate.

The effects of spray/wall interaction on diesel combustion and soot formation in a two-dimensional piston cavity were studied with a high speed color video camera in a constant volume combustion vessel. The two-dimensional piston cavity was applied to generate the impinging spray flame. In the cavity, the flat surface which plays a role as the cylinder head has a 13.5 degree angle with the injector axis and the impinging point was located 30 mm away from the nozzle tip. Three injection pressures of 100, 150, and 200 MPa and a single hole diesel injector (hole diameter: 0.133mm) were selected. The flame structure and combustion process were examined by using the color luminosity images. Two-color pyrometry was used to measure the line-of sight soot temperature and concentration by using the R and B channels of the color images. The soot mass generated by impinging spray flame is higher than that of the free spray flame.

Ethanol is regarded as the promising alternative fuel for gasoline to meet the strict low emission standard for spark ignition engines. In this study, the spray mixture formation process for different ethanol blended fuels, including E0 (gasoline), E85 (85% volume of ethanol and 15% volume of gasoline) and E100 (ethanol), has been evaluated using hole-type nozzle by the measurement of Laser Absorption Scattering (LAS) technique in a constant volume vessel. Based on the principle of LAS, the quantitative vapor and liquid phase distribution from different ethanol blended fuel can be obtained by the light extinction regime. Aiming to analyze the effect of mixture formation and evaporation for different components of blended fuel or pure gasoline and ethanol, the vapor distribution of gasoline was determined by using p-xylene, which had similar physical properties to gasoline, especially higher boiling temperature components, and higher absorption for ultraviolet.

The purpose of this study is to investigate the spray characteristics and ignition stability of gasoline sprays injected from a hole-type nozzle. Using a single-hole VCO (Valve-Covered-Orifice) nozzle, the spray characteristics were studied with LAS (Laser Absorption Scattering) technique, and then flame propagation and ignition stability were investigated inside a high temperature high pressure constant volume vessel using a high speed video camera. The spatial ignition stability of the spray at different locations was tested by adjusting the position of the electrodes. By adjusting the ignition timings, the stable ignition windows for 3 determined locations where the ignition stability was high at a fixed ignition timing were studied. The flame propagation process was examined using high speed shadowgraph method. Experimental results show that when the ignition points are located on the spray axis, the ignition probability is low.

Previous research has shown that the reduced nozzle hole diameter and elevated injection pressure are effective for preparing a uniform fuel-air mixture in a direct injection (D.I.) Diesel engine. A micro-hole nozzle with a hole diameter of 0.08 mm and an ultra-high injection pressure of 300 MPa have been employed to investigate the mixture formation process under various conditions. The aim of the current work is to clarify the effect of nozzle hole diameter and injection pressure on flame lift-off and soot formation processes. The free sprays from the micro-hole and conventional nozzles were investigated at a high-temperature, high-pressure constant volume vessel. A high-speed video camera system was employed to record the non-vaporizing sprays and combustion. The direct photography of OH chemiluminescence was used to provide information about the high temperature combustion process and to measure the flame lift-off length.

The fuel-ambient gas interaction process of the free diesel spray injected from the micro-hole nozzle (0.08 mm) into the quiescent and engine-like ambient gas condition was investigated by means of the laser-induced fluorescence - particle image velocimetry (LIF-PIV) technique in non-evaporating condition. Direct photography with high speed video camera and two color pyrometry were applied to analyze the evaporation spray and flame characteristics. Three injection pressures from 100, 200 to 300 MPa and two ambient gas densities of 11 and 15 kg/m₃ were selected as testing conditions. The entrained mass flow rate of the ambient gas through the whole spray boundary, the ratio of the total ambient gas entrainment rate to the fuel injection rate, etc., were calculated by using the ambient gas velocity data obtained by the LIF-PIV technique and used to correlate the combustion behavior.

The effect of injection pressure ranging from 100 to 300MPa on the ignition, flame development and soot formation characteristics of biodiesel fuel spray using a common rail injection system for direct injection (D.I.) diesel engine was investigated. Experiments were carried out in a constant volume vessel under conditions similar to the real engine condition using a single hole nozzle. Biodiesel fuels from two sources namely; palm oil (BDFp) and cooked oil (BDFc) with the commercial JIS#2diesel fuel were utilized in this research. The OH chemiluminescence technique was used to determine the ignition and the lift-off length of the combusting flame. The natural luminosity technique was applied to study the flame development and the two color pyrometry was applied for the soot formation processes. Ignition delay decreased as the injection pressure progressed from 100 to 300MPa. This was as a result of the enhanced mixing achieved at higher injection pressures.

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.

In this study, air entrainment, fuel evaporation and mixing process of diesel sprays injected by micro-orifices for direct-injection diesel engines were investigated at the end of injection transient and after the end of injection. The mixture formation process was analyzed using a laser absorption scattering (LAS) technique, providing the information of quantified liquid and vapor mass concentration, entrained air concentration and equivalence ratio. The data was obtained at the timings of quasi-steady state, sudden velocity decrease, the end of injection and after the end of injection. Two micro-orifices, which have different orifice diameters, were selected as test nozzles to investigate the end-of-injection characteristics at different nozzle geometries. In case of smaller orifice diameter, the liquid phase regression was observed around the end of injection, while it was not observed at larger orifice diameter due to denser liquid concentration near the nozzle tip.

The concept of two closely spaced micro-orifices (group hole nozzle) has been studied as a promising technology for the reduction of soot emission from direct injection (DI) diesel engines by improving the fuel atomization and evaporation. One of the main issues on group hole nozzle is the arrangement of orifices with various distances and angles. In this study, the ignition and combustion characteristics of wall-impinging diesel sprays from group-hole nozzles were investigated with various angles between two micro-orifices (included angles). A laser absorption scattering (LAS) technique for non-axisymmetric sprays, developed based on a LAS technique for axisymmetric spray, was applied to investigate the liquid/vapor mass distribution of wall-impinging sprays. The direct flame images and OH radical images inside a high pressure constant volume vessel were captured to analyze the effect of included angle on spray ignition and combustion characteristics.

Increasing injection pressure and decreasing nozzle hole diameter have been proved to be two effective approaches to reduce the exhaust emissions and to improve the fuel economy. Recently, the micro-hole nozzles and ultra-high injection pressures are applicable in commercial Diesel engines. But the mechanism of these two latest technologies is still unclear. The current research aims at providing information on the spray and mixture formation processes of the micro-hole nozzle (d=0.08mm) under the ultra-high injection pressure (Pinj=300MPa). The flat wall impinging sprays were focused on and the laser absorption-scattering (LAS) technique was employed to obtain the qualitative and quantitative information at both atmospheric and elevated conditions. The spray parameters were collected, the mixing rate was discussed, and the effects of various parameters on mixture formation were clarified.

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.

In order to investigate effects of the multi-hole nozzle with micro orifices on mixture formation processes in Direct-Injection Diesel engines, mixture characteristics were examined via an ultraviolet-visible laser absorption scattering (LAS) technique under various injectors. The injection quantity per orifice per cycle was reduced by nozzle hole sizes. The LAS technique can provide the quantitative and simultaneous measurements of liquid and vapor phases concentration distributions inside of the fuel spray. Mass of ambient gas entrained into the spray, liquid/ vapor mass and mean equivalence ratio of total fuel were obtained based on Lambert Beer's law. As a result, the leaner and more homogeneous fuel-gas mixture can be achieved by reducing the nozzle hole diameter, in the meanwhile more ambient gas were entrained into the spray. Moreover, relationships between mixture formation and D.I.

Experimental study has been carried out on the effects of the micro-hole nozzle injector and ultra-high injection pressure on the mixture properties of D.I. Diesel engine. A manually operated piston screw pump, High Pressure Generator, was used to obtain ultra-high injection pressures. Three kinds of injection pressures, 100MPa, 200MPa, and 300MPa, were applied to a specially designed injector. Four kinds of nozzle hole diameters, 0.16mm, 0.14mm, 0.10mm, and 0.08mm, were adopted in this study. The laser absorption-scattering (LAS) technique was used to analyze the equivalence ratio distributions, Sauter mean diameter, spray tip penetration length, and other spray characteristics. The analyses of the experimental results show that the micro-hole nozzle and ultra-high injection pressure are effective to increase the turbulent mixing rate and to form the uniform and lean fuel-air mixture.

The group-hole nozzle concept is regarded as a promising approach to facilitate better fuel atomization and evaporation for direct injection diesel engine applications. In the present work, the spray and mixture properties of group-hole nozzle with close, parallel or a small included angle orifices were investigated experimentally by means of the ultraviolet-visible laser absorption-scattering (LAS) imaging technique, in comparison with the conventional single-hole nozzle. Three series of group-hole nozzles were designed to investigate the effect of group-hole nozzle specification while varying the included angle and interval between the orifices. The results suggested that: 1) Group-hole nozzle with very close, parallel orifices presents the similar spray characteristics with those of the single-hole nozzle.

In the previous study of the authors, it was found that some benefits for the mixture preparation of DI gasoline engines can be offered by splitting the fuel injection, such as the phenomenon of high density liquid phase fuel piling up at the leading edge of the spray can be circumvented. In a further analysis, the vapor quantity in the “stable operating” range (equivalence ratio of vapor ϕv in a range of 0.7≤ϕv≤1.3) was significantly increased by the split injection compared to the single injection. In this work, the mechanism of the effect of the split injection on the mixture formation process was studied by combining the laser-sheet imaging, LIF-PIV and the LAS (Laser Absorption Scattering) technique. As a result, it is found that the spray-induced ambient air motion can help the formation of the more combustible mixture of the split injection whereas it played a minus role of diluting the spray by the single injection.

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.