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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.

Substantial amount of fuel energy input is lost by heat transfer through combustion chamber walls in the internal combustion engines. Thus, these heat losses account for reduced thermal efficiency, in that spray-wall impingement plays a crucial role in Direct Injection diesel engines. The objective of this study is to investigate the mechanism of the heat transfer from the spray/flame to the impinging wall under small diesel engine-like condition and how the spray characteristics are affected with regards to effect of injection pressure, nozzle hole diameter and impingement distance. The experiment results showed that injection pressure was predominant factor on spray-wall heat transfer.

The tiny and normal injection quantity instances usually happen under the multi-injection strategy condition to restrain the uncontrollability of the ignition timing of the homogeneous charge compression ignition (HCCI) combustion concept. Meanwhile, instead of the traditional and fundamental single-hole diesel injector, the axisymmetric multi-hole injectors are usually applied to couple with the combustion chamber under most practical operating conditions. In the current paper, the internal flow and spray characteristics generated by single-hole and multi-hole (10 holes) nozzles under normal (2 mm3/hole) and tiny (0.3 mm3/hole) injection quantity conditions were investigated in conjunction with a series of experimental and computational methods. High-speed video observation was conducted at 10000 and 100000 fps under the condition of 120 MPa rail pressure, 1.5 MPa ambient pressure, room temperature, and nitrogen environment to visualize different spray properties.

The effect of temporally-splitting high pressure injection on Diesel spray combustion and soot formation processes was studied by using the high-speed video camera. The spray was injected by the single-hole nozzle with a hole diameter of 0.11mm into the high-pressure and high-temperature constant volume vessel. The free spray and the spray impingement on the two dimensional (2D) piston cavity wall were examined. Injection pressures of 100 and 160 MPa for the single injection and 160 MPa for the split injection were selected. The flame structure and soot formation process were examined by using the two-color pyrometry. The soot generated in the flame under the split injection under 160 MPa becomes higher than that of the single injection under 160 MPa.

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.

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.

Although mixture formation is considered important in actual spark ignition engines, A full understanding of the combustion characteristics of a heterogeneous mixture has not yet been achieved. In this study, in order to clarify the effects of a heterogeneous concentration distribution of the fuel-air mixture on the flame propagation process, different degrees of heterogeneously distributed mixtures were created by the motion of a pair of perforated plates in a constant volume combustion chamber. The laser Rayleigh scattering method was applied for quantitative visualizations of these mixture distributions. To control the distribution of the mixture concentration and the turbulence intensity independently, the flow in the chamber and its turbulence intensity were also measured by a laser sheet method and the LDV technique.

An investigation on the effect of dwell time of split injection on a diesel spray evolution and mixture formation process was carried out. A commercial 7-hole injector were used in the experiment to eliminate the possible discrepancies on the spray with single-hole research injector. Laser absorption scattering (LAS) technique was implemented for the measurement of the temporal evolution of fuel evaporation and mixture concentration. The diesel surrogate fuel consists of n-tridecane and 2.5% of 1-methylnaphthalene in volume basis was used. The total amount of fuel injected was initially fixed to 5.0 mg/hole. A split ratio of 9: 1 in mass basis was selected according to the results obtained from a previous study. The dwell time was varied from 120 µs to a negative value of −50 µs. The effects of negative dwell time was not ideal for lean mixture formation when compared to zero or positive dwell time conditions.

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.

An experimental study was conducted to investigate the flame propagation characteristics in the presence of a heterogeneous concentration distribution of a fuel-air mixture in order to provide fundamental knowledge of the effects of gaseous mixture concentration heterogeneity on the combustion process. Different propane-air mixture distributions were produced by the reciprocating movements of a pair of perforated plates in a constant volume combustion chamber. The mean equivalence ratio of the fuel-air mixture was varied from 0.7 on the lean side to 1.6 on the rich side, the turbulence intensity in the combustion chamber was also varied at levels of 0.185 m/s, 0.130 m/s, 0.100 m/s, and 0.0 m/s. By an independent control of the mixture distribution and the turbulence intensity in the combustion chamber, the flame structure and flame propagation speed at various heterogeneous levels of the mixture distribution were investigated in detail.

A comprehensive model for sprays emerging from high-pressure swirl injectors in DISI engines has been developed accounting for both primary and secondary atomization. The model considers the transient behavior of the pre-spray and the steady-state behavior of the main spray. The pre-spray modeling is based on an empirical solid cone approach with varying cone angle. The main spray modeling is based on the Liquid Instability Sheet Atomization (LISA) approach, which is extended here to include the effects of swirl. Mie Scattering, LIF, PIV and Laser Droplet Size Analyzer techniques have been used to produce a set of experimental data for model validation. Both qualitative comparisons of the evolution of the spray structure, as well as quantitative comparisons of spray tip penetration and droplet sizes have been made. It is concluded that the model compares favorably with data under atmospheric conditions.

Experiments and modeling of the fuel spray trajectory and dispersion influenced by both a swirling gas flow and wall impingement were performed under simulated direct injection (D.I.) diesel engine conditions at a high pressure and high temperature. A spray was injected into the steady swirling gas flow and impinged on the simulated piston cavity wall in a constant-volume bomb. High-speed Schlieren photographs provided the informative data on the behavior of the spray vaporizing in such diesel-like circumstances. A simplified computational model was developed to describe the spray trajectory and the fuel vapor dispersion in the D.I. diesel combustion chamber. The model includes the effects of the breakup on the trajectory and the vaporization of the spray, and the effects of the swirling gas flow and the wall impingement on the dispersion of the fuel vapor.

The ignition and flame propagation processes of a propane-air mixture compounded with a kerosene spray were investigated in order to allow a better understanding of the multi-phase combustion process of the spray compound mixture in a direct injection stratified charge (DISC) engine. The ignition probability and the flame propagation velocity, as functions of the overall equivalence ratio, fraction of propane in the fuel, ignition energy and the Sauter mean diameter of the spray, were measured under atmospheric conditions. The development of the flame kernel and the propagating flame were observed by a high-speed video camera combined with a schlieren system. Adding small amounts of the kerosene spray to the lean propane-air mixture improved the ignition probability. However, the ignition probability depended strongly on the Sauter mean diameter and the ignition energy. Replacing the propane with the kerosene spray in a rich propane-air mixture increased the flame propagation velocity.

A pancake-type constant-volume combustion chamber was used to investigate the combustion and NOx emission characteristics of propane-air and hydrogen-air mixtures under various charge stratification patterns, which were obtained by variations of the initial charge and injected mixture concentrations and the ignition spark timing. A planar laser-induced fluorescence from nitrogen dioxide as gas fuel tracer was applied to measure the mixture distribution in the test chamber. The second harmonic output of pulsed Nd; YAG laser was used as a light source for fluorescence excitation. The fluorescence images were corrected by a gated image-intensified CCD camera. The quantitative analysis of fuel concentration was made possible by the application of linearity between fluorescence intensity and NO2 concentration at low trace level.

Increasing the injection pressure and splitting the injection stage are the major approaches for a diesel engine to facilitate the fuel-air mixture formation process, which determines the subsequent combustion and emission formation. In this study, the free spray was injected by a single-hole nozzle with a hole-diameter of 0.111 mm. The impinging spray, formed by a two-dimensional (2D) piston cavity having the same shape as a small-bore diesel engine, was also investigated. The injection process was performed by both with and without pre-injection. The main injection was carried out either as a single main injection with injection pressure of 100 MPa (Pre + S100) or a split main injection with 160 MPa defined by the mass fraction ratio of 3:1 (Pre + D160_3-1). The tracer Laser Absorption Scattering (LAS) technique was adopted to observe the spray mixture formation process. The ignition delay/location and the soot formation in the spray flame were analyzed by the two-color method.

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”.

A comparison of spray characteristics was conducted between single- and multi-hole injectors. A commercial software (AVL FIRE) was used to investigate the internal flow inside the sac volume, as well as the initial spray behavior at 1 mm downstream of the nozzle exit. Microscopic imaging was applied to observe the spray dispersion angle (spray cone angle) at the vicinity of the nozzle. Laser absorption scattering (LAS) technique was implemented for measuring the mixture concentration. Three injection quantities, namely 0.5, 2.5, and 5.0 mg/hole, were selected to observe the differences between transient and quasi-steady spray. The vapor penetration at the initial stage of the injection was greater for single-hole than that of multi-hole injector due to faster fuel pressure build-up process inside the sac volume.

This paper presents the experimental analysis for the turbulence in the combustion chamber of a direct injection (D.I.) diesel engine. A dual beam mode, forward-scattering laser doppler velocimeter was applied to the flow measurement in a four-stroke, single-cylinder direct injection diesel engine of 110 mm bore and 125 mm stroke. The turbulence component was separated from instantaneous velocity using a high-pass filter. As a result, the difference in turbulent intensity between the intake and compression processes was discussed. Also, the effect of intake port and piston cavity shapes, the compression ratio and the engine speed on the turbulent intensity were clarified. In addition, the empirical equation for the decay of turbulent intensity in the compression process was expressed by a function of the Reynolds number based on the mean swirling flow.

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.

A mathematical model was developed for predicting the concentration of exhaust nitric oxide, soot and other emissions in a direct injection diesel engine. In the model, it was emphasized to describe the phenomena occurring in the combustion chamber from the microscopic point of view. The prediction was based on the knowledges concerning a single droplet as well as the droplet size distribution in a fuel spray and the spatial and temporal distribution histories of fuel in a combustion chamber. The heterogeneous field of temperature and equivalence ratio, and uniform pressure in the cylinder were postulated. The heat release model gives the burning rate of injected fuel and pressure and temperature history in the cylinder. The concentration of nitric oxide and soot in the cylinder was predicted by the emission formation model.