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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”.

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.

An experimental study was made of the two-dimensional distributions of the fuel vapor concentration simulated by Freon-12 in the combustion chamber of a SI engine. Laser Rayleigh scattering was applied for this remote, nonintrusive and highly space- and time-resolved measurement. The original engine was modified to introduce YAG laser-induced sheet light into the combustion chamber and the scattered light was captured by a CCD camera fitted with a gated double-microchannel plate image intensifier. The results showed that the fuel vapor concentration was highly heterogeneous during the intake stroke and the inhomogeneity decreased in the compression stroke. But, even at the end of the compression stroke, a number of small lumps of inhomogeneous mixture still existed randomly in the engine combustion chamber, which is assumed to cause the heterogeneity of the mixture strength field at the spark discharge.

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.

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.

Quantitative imaging of the fuel concentration distribution was made in the combustion chamber of a propane-fueled spark ignition (SI) engine with the employment of laser-sheet-induced Rayleigh scattering technique for realizing the remote, nonintrusive and highly space- and time-resolved measurement. The original engine was modified to introduce YAG laser-induced sheet light into the combustion chamber and the scattered light was captured by a CCD camera fitted with a gated double-micro- channel plate image intensifier. The measurements were done at the crank angle of 270°ATDC in the combustion chamber of the engine motored at 200rpm with an air fuel ratio of 13 for various injection timing, injection direction and intake flow. The results show that with an appropriate matching of fuel injection timing, injection direction and intake flow, a stratified distribution of the fuel concentration can be realized.

A new technique was proposed for the simultaneous measurement of the concentration of fuel vapor and liquid in an evaporating diesel spray injected into a high temperature and high pressure environment. This technique was based on the principle of the absorption of ultraviolet laser light by fuel vapor and the scattering of visible laser light by fuel droplets in the diesel spray. For this principle, α-methylnaphthalene was used as a test fuel. Measuring the transmissivity of ultraviolet and visible laser lights absorbed and scattered by β-methylnaphthalene spray made it possible to analyze the fuel vapor concentration, droplets density and the mixture temperature in the diesel spray. A computerized tomographic transfer technique was also adopted to analyze three-dimensional fuel concentration distribution in the spray.

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.

Planar laser-induced fluorescence (PLIF) technique was employed to perform the quantitative measurements of the cyclic variation of mixture concentration in the combustion chamber of a spark ignition (SI) engine. Nitrogen dioxide was used as the fluorescence tracer to simulate the fuel vapor. A Nd:YAG laser operated at its second harmonic wavelength was employed as the light source. The original engine was modified to introduce laser sheet light into the combustion chamber and the induced fluorescence was captured by a CCD camera fitted with a gated image intensifier. The measurements were done at the engine crank angles of 180° ∼ 300° ATDC with the engine speeds of 200 ∼ 400 rpm and the injection timings of -70 °, 50° and 100° ATDC. A theoretical analysis was made to describe the cyclically varying characteristics of the mixture concentration.

Experiments and modeling of a spray impinged onto a cavity wall of a simulated piston were performed under simulated diesel engine conditions (pressure and density) at an ambient temperature. The diesel fuel was delivered from a Bosch-type injection pump to a single-hole nozzle, the hole being drilled in the same direction as the original five-hole nozzle. The fuel was injected into a high-pressure bomb in which an engine combustion chamber, composed of a piston, a cylinder head and a cylinder liner, was installed. Distributions of the spray impinged on the simulated combustion chamber were observed from various directions while changing some of the experimental parameters, such as combustion chamber shape, nozzle projection and top-clearance. High-speed photography was used in the constant volume bomb to examine the effect of these parameters on the spray distributions.

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.

Distributions of non-evaporating diesel sprays impinging on a simulated combustion chamber wall were observed from various directions while changing some of the experimental parameters, such as nozzle projection and top-clearance. High-speed photography was used in this study to examine the effects of these parameters on the spray distributions. Moreover, the spray distributions were predicted by using a spray model based on a multi-package model. The calculated distributions were displayed three-dimensionally using a volume rendering application developed by the authors. The predicted spray distributions were compared with the experimental results observed from various directions in order to evaluate the spray model.

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.

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.

Simplified visualization of the fuel spray developing process in a small D.I. diesel engine was made by the liquid injection technique. In this technique, a liquid fuel was injected into another liquid to simulate injection into a high pressure gaseous atmosphere. For obtaining spray characteristics in the liquid similar to a diesel spray in a high-pressure gaseous atmosphere, the similarity principles based on the Reynolds number of the fuel flow at a nozzle hole and empirical equations of the spray penetration including the breakup length were introduced in this study. Especially, the injector was newly designed for the liquid injection technique based on these similarity principles. The behavior of the spray in a swirling flow was investigated. The spray with different breakup length shows different behavior in the same swirling flow.

A simple, but useful method is described for predicting the swirl speed during the compression process in a direct injection diesel engine. The method is based on the idea of dividing the combustion chamber into two volumetric regions and computing the variation of the angular momentum in each region. Laser doppler velocimeter measurements in a motored engine proved the validity of the idea that the volume in the combustion chamber should be treated as two regions, that is, the cylindrical volume inside the piston-cavity radius, and the annular volume outside the piston-cavity radius. Distributions of tangential velocities were measured for different conditions, including the intake port configuration, the piston cavity shape, the compression ratio and the engine speed. These results were integrated in the two regions and provided the measured “two volume-regions” swirl ratio. At the same time, the computation was carried out for the same experimental conditions.

This paper describes a simplified three-dimensional modeling of the mixture formation and combustion processes in a direct injection (D.I.) diesel engine. The fuel-air mixing and combustion processes in the D.I. diesel engine can be characterized by the combined effects of some processes, such as spray trajectory, fuel vaporization, gas motion, combustion, and dispersion of gaseous components and enthalpy. Each process was computed by a simple sub-model based on the experimental results and empirical equations. The dispersion process was, however, computed by solving the conservation equations of the gaseous components and enthalpy by the finite difference technique. The sub-models were combined for predicting the three-dimensional distributions of the gaseous components and the temperature in the combustion chamber, and finally the cylinder pressure, heat release rate, engine performance and pollutant emissions (NO and soot).

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.

New empirical equations to represent the Sauter mean diameter of a spray injected by a diesel nozzle are presented in this paper. In order to determine the new equations, drop sizes of a diesel spray were analyzed by a laser diffraction technique. Liquids with different viscosities and different surface tensions were tested to obtain the generalized empirical equations. The maximum injection and maximum ambient pressures were 90 MPa and 3.0 MPa respectively. Both the minimum value of the injection pressure to produce a fine spray and the Sauter mean diameter increase the greater the viscosity and the surface tension of the liquid. At a high injection velocity, the Sauter mean diameter increases with an increase in ambient pressure, but it decreases when ambient pressure is increased at a low injection velocity.