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The authors have explored the potential of fuel to control spray and its combustion processes in a diesel engine. Fuel has some potential for low emission and high thermal efficiency because its volatility and ignitability are one of the ultimate performing factors of the engines. In present study, the ignition process of mixed fuel spray was investigated in a constant volume combustion vessel and in a rapid compression and expansion machine, The ignition delay based on the diagram of rate of the heat release, the imaging of natural flame emissions and the numerical simulation were carried out to clarify the effect of the physical and chemical properties of mixed fuel on ignition characteristics.

This study proposes a hybrid model which consists of modified TAB(Taylor Analogy Breakup) model and DVM(Discrete Vortex Method). In this study, the simulation process is divided into three steps. The first step is to analyze the breakup of droplet of injected fuel by using modified TAB model. The second step based on the theory of Siebers' liquid length is analysis of spray evaporation. The liquid length analysis of injected fuel is used for connecting both modified TAB model and DVM. The final step is to reproduce the ambient gas flow and inner vortex flow injected fuel by using DVM. In order to examine the hybrid model, an experiment of a free evaporating fuel spray at early injection stage of in-cylinder like conditions had been executed. The numerical results calculated by using the present hybrid model are compared with the experimental ones.

This paper presents an atomization mechanism of a spray injected into the low-pressure field, as the subject of injection system in a suction manifold of gasoline engine. Pure liquid fuel, which is n-Pentane or n-Hexane is injected into quiescent gaseous atmosphere at room-temperature and low- pressure through pintle type electronic control injector. Fuel sprays are observed by taking photographs for variation of the back pressure and the changes in spray characteristics with the back pressure below atmospheric pressure are examined in detail. In particular, in the case of the back pressure below the saturated vapor pressure of fuel, the atomization mechanism is discussed from a viewpoint of flash boiling phenomena, those are bubble growth rate and so on.

In a small high-speed DI diesel engine, injected fuel sprays impinge on the wall of piston cavity. Discussion and analysis of the combustion phenomena in the diesel engine demand the measurement of the characteristics of the impinging spray. In the experiments presented here, diesel fuel oil was injected into a high pressure chamber in which compressed air or CO2 gas at room temperature was charged. The single spray was impinged on a flat wall at a normal angle. The growth of the spray was photographed, not only with transmitted light but also with scattered light through a narrow slit. The temporal and spatial distribution of the droplets density in the impinging spray applying the concentric circle model was calculated using the data of the laser light extinction method. From these results, the detailed information concerning the droplets density in the impinging diesel spray was obtained.

Diesel sprays injected into a combustion chamber of a small sized high-speed CI engine impinge surely on a piston surface and a cylinder wall. As a consequence, their vaporization, mixture formation and combustion processes are affected by impingement phenomena. And the other important factors affecting on the processes is the injection pressure. Then, the distribution of the vapor concentration in a single diesel spray impinging on a flat and hot wall was experimented by the exciplex fluorescence method, as a simple case. The injection pressure was varied in the range from 55 MPa to 120 MPa. It is found that the distribution of the vapor concentration in this case is much leaner than that in the case of the low injection pressure of 17.8MPa.

The premixed charge compression ignition (PCCI) combustion in a compression ignition (Cl) engine is one of countermeasures against the very much severe regulation for exhaust gas of engine out. The authors have been proposed to use the fuel mixed with high volatility component and low volatility component to actualize PCCI combustion. This kind of fuel injected forms a fine and lean spray by the flash boiling phenomena which depends on the pressure and the temperature. The role of the former fuel is to decrease in the generation of particulate matters (PM) and that of the latter one is to break out the ignition. Thus, it is very much significant to find the distribution of vapor concentration of both fuels in a spray. This paper describes both distributions in a single diesel spray by use of the technique of laser induced fluorescence (LIF) in a constant volume chamber with high temperature at high pressure as the fundamental research.

In this paper, spray characteristics were examined to deduce the effect of ambient gas properties. Considered ambient properties were the viscosity μa and density ρa, and thus the kinematic viscosity νa. The objective of this paper is to reveal the effect of compressibility of the ambient gas to spray formation. In the experiments, the changed ranges were And a standard-sac volume nozzle of hole diameter dn =0.25 mm (ln/dn=3.0) was used at constant injection pressure difference (Δp=16.2 MPa). Also the injection pressure was varied in the range of 55 to 120 MPa with a mini-sac volume nozzle of hole diameter dn =0.20 mm (ln/dn =5.5). Several different gases were used to change the ambient viscosity at a room temperature. From the experiments, it is obtained that larger the viscosity, the more the spray spreads in the radial direction, thus the spray angle gets larger and the tip penetration became shorter.

LES of non-evaporative diesel spray have been performed to investigate the effects of breakup models of Modified TAB, WAVE and KHRT model on computational results. KIVALES that is LES version of KIVA code was used for base code. In our KIVALES, CIP scheme was incorporated in order to suppress the numerical diffusion. Results showed that the breakup model is significantly affected on the calculated spray shape, because the droplet diameter determined by breakup models affects on the transmittance of the droplet momentum into the ambient gas, the evolution of the vortex structure in the gas phase and the droplet dispersion by the vortex structure.

In this study, a numerical experiment using a 2D convective equation and LES of an evaporative diesel spray for different convective schemes has been performed to examine effects of convective schemes on a fuel-air mixture formation of the diesel spray simulation and to determine the convective scheme used in KIVALES. In addition to KIVALES original schemes, such as QSOU, PDC and IDC, CIP was incorporated into KIVALES in order to calculate the convective terms with low numerical diffusion. The numerical experiment using the 2D convective equation showed that the numerical diffusion of CIP scheme was lowest in the convective schemes used in present study. However CIP scheme used was not a monotone scheme completely due to the overshoot and the undershoot of the scalar provided near the boundary. Hence, CIP scheme was employed for only the convective term of the LES momentum equation, while the other convective schemes were calculated using QSOU, which is a monotone scheme.

This work presents the ignition delay time characteristics of oxygenated fuel sprays under simulated diesel engine conditions. A constant volume combustion vessel is used for the experiments. The fuels used in the experiments were three oxygenated fuels: diethylene glycol dibutyl ether, diethylene glycol diethyl ether, and diethylene glycol dimethyl ether. JIS 2nd class gas oil was used as the reference fuel. The ambient gas temperature and oxygen concentration were ranging from 700 to 1100K and from 21 to 9%, respectively. The results show that the ignition delay of each oxygenated fuel tested in this experiments exhibits shorter than that of gas oil fuel for the wide range of ambient gas conditions. Also, NTC (negative temperature coefficient) behavior which appears under shock tube experiment for homogenous fuel-air mixture was observed on low ambient gas oxygen concentration for each fuel. And at the condition, the ignition behavior exhibits two-stage phase.

Considering the bell-shaped temperature dependence of soot particle formation, the control of flame temperature has a possibility to drastically suppress of soot formation. Furthermore, oxygenated fuels are very effective on soot reduction, and the use of these kinds of fuels has a potentiality for smokeless diesel combustion. In this paper, the effects of flame lift-off and flame temperature on soot formation in oxygenated fuel sprays were experimentally investigated using a constant volume combustion vessel which simulated diesel engine conditions. The diffusion flame lift-off length was measured in order to estimate the amount of the oxygen entrained upstream of the flame lift-off length in the fuel jet. This was determined from time-averaged OH chemiluminescence imaging technique. Also, the flame temperature and soot concentration were simultaneously evaluated by means of two-color method.

Soot formation process inside the combustion chamber of an DI diesel engine is focused as a phenomenological basic scheme by using several optical diagnostics technique for the improvement of diesel exhaust emission. We have conducted the series of optical measurement research for the clarification of combustion field in an DI diesel engine. Then, this paper is a kind of review by adding the fuel vapor properties and particle image velocimetry (PIV) analysis with focusing the soot formation process. The experiments were carried out in a small sized high-speed DI diesel engine installed with an optical access view. The spray characteristics and its flow field in 2-D field were measured by laser sheet scattering (LIS) method and PIV scheme.

This paper presents the experimental study on the characteristics of a transient gas jet. Helium was injected instantaneously into a quiescent atmosphere with constant pressure. The distributions of instantaneous static pressure, radial and axial velocities and concentration at measuring points in the jet, which is obtained by the statistical data processing, are discussed to explain a transient mixture formation in the jet. The analogy between this jet and a diesel spray as for this mixture formation are also discussed by using these results.

In previous our work, we revealed that the flash boiling process could improve remarkably the spray atomization for the pure substance-single component fuel in relation to the port-injected S.I. engines. Then, we applied this flash boiling spray to the Diesel spray process by the use of the two phase region formed between liquefied CO2 and n-Tridecane as the first step of fuel design concept. And the promoted atomization properties could be obtained in this mixed fuel concept. Further, we could obtain the simultaneous reduction of NO and soot emissions in Diesel engine exhaust due to the spray internal EGR effect and reburning of soot. As the second step, we proposed a novel fuel design concept for low exhaust emission and combustion control, relating to mixed and reformulated fuels with a lower boiling point fuel such as gasoline components or gas fuel and a higher boiling point fuel such as gas oil or heavy oil components to obtain the both advantages of their fuels for combustion.

In this study, the novel fuel design concept has been proposed in order to realize the low emission and combustion control in engine systems. In this fuel design concept, the mixed fuels with a high volatility fuel (gasoline or gaseous fuel components) and a low volatility fuel (gas oil or fuel oil components) are used in order to improve the spray characteristics by flash boiling. In our previous papers on this study, the fundamental characteristics of spray and its combustion of mixed fuel were reported. In this paper, heat release and exhaust emission (smoke, NOx and THC) characteristics of single cylinder diesel engine operated with the mixed fuels were investigated under each load. The exhaust performance of diesel engine could be improved using mixed fuel, because fuel properties and spray characteristics were controlled by changing mixing fraction of the mixed fuel.

It is significant for understanding the phenomena in a stratified charge engine and an SI engine with direct injection system to carry out the fundamental research. The experiments were conducted in a constant volume chamber with atmospheric condition. The pre-mixed charge composed of ethylene and air was charged with various equivalence ratio, the second charge with the same composition was injected into the chamber, thereafter, the combustion started by a spark plug. The phenomena were analyzed by use of the experimental results of shadowgraph, [OH] natural emission, pressure history and NOx and UHC in the exhaust gas.

As authors reported in SAE Trans. 800968, entitled “Investigation on the Characteristics of Diesel Fuel Spray”, the flame never proceeds into the initial-part of the spray during injection. The length of the initial part-lies within 10 to 15 mm regardless of the conditions of the injection systems and of the ambient conditions. The ignition delay does not decrease but becomes constant when the ambient temperature or the pressure exceed a discrete value. The authors would like to propose a new concept of “Spray Formation Delay” during which the field is generated where the physical and chemical delay can exist. The spray formation delay is one of the major factors which control the above mentioned limitation of ignition delay. The characteristics of the spray formation delay are investigated and clarified.

Three-dimensional large eddy simulation (LES) has been conducted for a diesel spray flame using KIVALES which is LES version of KIVA code. Modified TAB model, velocity interpolation model and rigid sphere model are used to improve the prediction of the fuel-mixture process in the diesel spray. Combustion is simulated using the Eddy-Dissipation model. CIP method was incorporated into the KIVALES in order to suppress the numerical instability on the combustible flow. The formation of soot and NO was simulated using Hiroyasu model and KIVA original model. Three different grid resolutions were used to examine the grid dependency. The result shows that the LES approach with 0.5 mm grid size is able to resolve the instantaneous spray with the intermittency in the spray periphery, the axi-symmetric shape and meandering flow after the end of injection as shown in the experimental results.

Large Eddy Simulation (LES) is applied to non-evaporative and evaporative diesel spray simulations. KIVALES, which is LES version of KIVA code, is used as the LES computational code. Modified TAB model is used as breakup model, and interpolated donor cell differencing scheme is employed to calculate convective terms. To validity LES simulation, LES results using KIVALES are compared with experimental results and simulated results with conventional RANS approach using KIVA3V res.2. The results show that the LES simulation of non-evaporative spray depends on the grid size in comparison with RANS simulation, and good agreement is obtained between experimental results and the LES results with fine grid (720,000 cells). Furthermore, asymmetric non-evaporative spray which has intermittency at the outer edge of sprays is simulated, since instantaneous turbulent flow field can be predicted directly in LES case.

In SI engines with port injection system, the injected fuel spray adheres surely on the port wall and the inlet valve, consequently, the spray-wall interaction process leads to the generation of unburned hydrocarbons and uncontrollable mixture formation. This paper deals with the fuel mixture preparation process including basic research on characteristics of the wall-wetted fuel film on a flat wall inside a constant volume vessel. In the experiments, iso-octane mixed with biacetyl as a tracer dopant was injected through a pintle type injector against a flat glass wall under the ambient conditions of atmospheric pressure and room temperature. The thickness of the adhered fuel film on the wall was quantitatively measured by using laser induced fluorescence (LIF) technique, which provides 2-D distribution information with high special resolution as a function of the injection duration, the impingement distance from the injector to the wall, and the impingement angle against the wall.