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An experimental study on emission formation processes, such as these of nitric oxide, particulate and total hydrocarbon in a small direct injection (D.I.) diesel engine was carried out by using a newly developed total in-cylinder sampling technique. The sampling method consisted of rapidly opening a blowdown valve attached to the bottom of the piston bowl, and quickly transferring most of the in-cylinder contents into a large sampling chamber below the piston. No modification of the intake and exhaust ports in a cylinder head was required for the installation of the blowdown apparatus. The sampling experiment gave a history of spatially-averaged emission concentrations in the cylinder. The effects of several engine variables, such as the length-to-diameter ratio of the nozzle hole, the ratio of the piston bowl diameter to the cylinder bore and the intake swirl ratio, on the emission formation processes were investigated.

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.

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.

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.

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.

Cross-sectional distributions of the liquid phase temperatures in fuel sprays were measured using a laser-induced fluorescence technique. The liquid fuel (n-hexadecane or squalane) was doped with pyrene(C16H10). The fluorescence intensity ratios of the pyrene monomer and excimer emissions has temperature dependence, and were used to determine the liquid phase temperatures in the fuel sprays. The measurements were performed on two kinds of sprays. One was performed on pre-heated fuel sprays injected into surrounding gas at atmospheric conditions. The other was performed on fuel sprays exposed to hot gas flow. The spray was excited by laser radiation at 266nm, and the resulting fluorescence was imaged by an intensified CCD camera. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence image by the temperature dependence of the intensity ratio.

A calculative investigation was performed in order to examine the effects of injection rate profile and air entrainment characteristics on exhaust emission using a phenomenological spray combustion model. The calculations were made of an engine with a bore of 114 mm and a stroke of 130 min while changing the injection rate profile and the air entrainment characteristics. As a result of the calculations, effective measures were found for simultaneous reduction of NOx and smoke emissions.

The two-dimensional distributions of the liquid phase temperatures in diesel sprays injected into high-pressure and high-temperature environments were measured using the laser-induced fluorescence technique. The liquid fuel (n-hexadecane) was doped with pyrene(C16H10). The fuel spray doped with pyrene was injected under a high-pressure of 3.1MPa and a high-Temperature of 773K. The evaporating diesel spray was excited by laser radiation at 266nm, and the resulting fluorescence was imaged by an intensified CCD camera. The fluorescence intensity ratios of the pyrene monomer and excimer emissions have temperature dependence, and were used to determine the liquid phase temperatures in the diesel sprays. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence images by the temperature dependence of the intensity ratio.

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.

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.

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.

The effects of engine parameters, such as spray characteristics and combustion chamber geometry on performance and exhaust emissions in a small D.I. diesel engine were investigated to find out the optimum way of improving the engine. Diesel spray injected into a high-pressure vessel was photographically analyzed to guess the spray behavior in a firing diesel engine. The ratio of hole length to the diameter of a nozzle (L/D) was varied from 3 to 7 as the main parameter of the nozzle. Piston cavity diameter and intake swirl were chosen as the other parameters. The effect of the above parameters was investigated in terms of brake specific fuel consumption (BSFC), exhaust smoke, nitric oxides (NOx) and total hydrocarbon (THC). The L/D of the nozzle is concluded to be of major importance in terms of BSFC and THC emission. Smaller piston cavity diameters lead to lower exhaust smoke, but to a higher level of NOx emission.

A new optical measuring technique of tip penetration of a diesel fuel spray was developed by detecting the arrival times of the spray tip at several light sheets which were preset at various axial locations downstream. Verified by the instantaneous photographic technique, it was confirmed that this technique is effective, with sufficient accuracy, for measuring the spray tip penetration much more easily than the conventional photographic technique. The tip penetrations of diesel sprays injected through single-hole nozzles with various orifice lengths and diameters has been investigated over a wide range of the operating conditions by this technique. The spray injected through two multihole nozzles, either with or without a sac volume, has also been characterized. The results showed that the spray tip penetration is affected somewhat by the operating conditions. Eventually it is affected by the injected fuel momentum flowrate, nozzle geometry and ambient gas density.