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Journal Article

Simultaneous Reduction of Pressure Rise Rate and Emissions in a Compression Ignition Engine by Use of Dual-Component Fuel Spray

Ignition, combustion and emissions characteristics of dual-component fuel spray were examined for ranges of injection timing and intake-air oxygen concentration. Fuels used were binary mixtures of gasoline-like component i-octane (cetane number 12, boiling point 372 K) and diesel fuel-like component n-tridecane (cetane number 88, boiling point 510 K). Mass fraction of i-octane was also changed as the experimental variable. The experimental study was carried out in a single cylinder compression ignition engine equipped with a common-rail injection system and an exhaust gas recirculation system. The results demonstrated that the increase of the i-octane mass fraction with optimizations of injection timing and intake oxygen concentration reduced pressure rise rate and soot and NOx emissions without deterioration of indicated thermal efficiency.
Technical Paper

Effects of Mixedness and Ignition Timings on PCCI Combustion with a Dual Fuel Operation

A dual fuel operation with different reactivity fuels has the possibility of optimizing performance and emissions in premixed charge compression ignition engines by controlling the spatial concentration and distribution of both fuels. In the present study, n-heptane and i-octane were independently injected through two different injectors. In-cylinder pressure analysis and emissions measurement were performed in a compression ignition engine. Injection timings, fuel quantity ratio between the injections were changed for the two cases, in which one fuel was injected using a port fuel injection system while the other was directly injected into the cylinder, in order to drastically vary mixture distributions and ignition timings. In addition, an optical diagnostic was performed in a rapid compression and expansion machine to develop an understanding of the ignition processes of the two mixtures.
Technical Paper

Chemical Kinetics Study on Ignition Characteristics of Biodiesel Surrogates

Methyl butanoate (MB) and methyl decanoate (MD) are surrogates for biodiesel fuels. According to computational results with their detailed reaction mechanisms, MB and MD indicate shorter ignition delays than long alkanes such as n-heptane and n-dodecane do at an initial temperature over 1000 K. The high ignitability of these methyl esters was computationally analyzed by means of contribution matrices proposed by some of the authors. Due to the high acidity of an α-H atom in a carbonyl compound, hydroperoxy radicals are generated out of the equilibrium between forward and backward reactions of O₂ addition to methyl ester radicals by the internal transfer of an α-H atom in the initial stage of an ignition process. Some of the hydroperoxy methyl ester radicals can generate OH to activate initial reactions. MB has an efficient CH₃O formation path via CH₃ generated by the β-scission of an MB radical which has a radical site on the α-C atom to the carbonyl group.
Technical Paper

Visualization of the Cavitating Flow inside the Nozzle Hole Using by Enlarged Acrylic Nozzle

In this study, it is purpose to make clear the effect of cavitation phenomenon on the spray atomization. In this report, the cavitation phenomenon inside the nozzle hole was visualized and the pressure measurements along the wall of the nozzle hole were carried out by use of 25-times enlarged acrylic nozzle. For the representatives of regular gasoline, single and two-component fuels were used as a test fuel. In addition, various cavitating flow patterns same as experimental conditions were simulated by use of Barotropic model incorporated in commercial code of Star-CD scheme, and compared with experimental results.
Journal Article

Modeling of Auto-Ignition and Combustion Processes for Dual-Component Fuel Spray

Auto-ignition and combustion processes of dual-component fuel spray were numerically studied. A source code of SUPERTRAPP (developed by NIST), which is capable of predicting thermodynamic and transportation properties of pure fluids and fluid mixtures containing up to 20 components, was incorporated into KIVA3V to provide physical fuel properties and vapor-liquid equilibrium calculations. Low temperature oxidation reaction, which is of importance in ignition process of hydrocarbon fuels, as well as negative temperature coefficient behavior was taken into account using the multistep kinetics ignition prediction based on Shell model, while a global single-step mechanism was employed to account for high temperature oxidation reaction. Computational results with the present multi-component fuel model were validated by comparing with experimental data of spray combustion obtained in a constant volume vessel.
Technical Paper

Large Eddy Simulation of Non-Evaporative and Evaporative Diesel Spray in Constant Volume Vessel by Use of KIVALES

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.
Technical Paper

A Fundamental Study on Ignition Characteristics of Two-Component Fuel in a Diesel Spray

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.
Technical Paper

Effect of Breakup Model on Diesel Spray Structure Simulated by Large Eddy Simulation

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.
Technical Paper

Large Eddy Simulation of Diesel Spray Combustion with Eddy-Dissipation Model and CIP Method by Use of KIVALES

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.
Technical Paper

Effect of Octane Rating and Charge Stratification on Combustion and Operating Range with DI PCCI Operation

A single cylinder engine has been run with direct-injection premixed charge compression ignition (PCCI) operation. The operation is fueled with primary reference fuels for a wide variety of injection timing and equivalence ratio to investigate the effect of charge stratification and octane rating on PCCI combustion. The test results showed that although the change of the injection timing can gain the high combustion efficiency for a wide range of equivalence ratio, the combustion phasing where the high combustion efficiency is accomplished is not varied only by changing the injection timings. Therefore, the only change of injection timings does not improve the thermal efficiency which is influenced by the combustion phasing. On the other hand, at the fixed compression ratio, inlet air temperature and so on, the octane rating is useful in altering the combustion phasing.
Technical Paper

Study on Characteristics of Auto-Ignition and Combustion of Unsteady Synthetic Gas Jet

It is thought that the synthetic gas, including hydrogen and carbon monoxide, has a potential to be an alternative fuel for internal combustion engines, because a heating value of the synthetic gas is higher than one of hydrogen or natural gas. A purpose of this study is to acquire stable auto-ignition and combustion of the synthetic gas which is supposed to be applied into a direct-injection compression ignition engine. In this study, the effects of ambient gas temperatures and oxygen concentrations on auto-ignition characteristics of the synthetic gas with changing percentage of hydrogen (H2) or carbon monoxide (CO) concentrations in the synthetic gas. An electronically-controlled, hydraulically-actuated gas injector was used to control a precise injection timing and period of gaseous fuels, and the experiments were conducted in an optically accessible, constant-volume combustion chamber under simulated quiescent diesel engine conditions.
Technical Paper

Spray and Combustion Characteristics of Reformulated Biodiesel with Mixing of Lower Boiling Point Fuel

Authors propose the reformulation technique of physical properties of Biodiesel Fuel (BDF) by mixing lower boiling point fuels. In this study, waste cooking oil methyl ester (B100), which have been produced in Kyoto city, is used in behalf of BDF. N-Heptane (C7H16) and n-Dodecane (C12H26) are used as low and medium boiling point fuel. Mixed fuel of BDF with lower boiling point fuels have lighter quality as compared with neat BDF. This result is based on the chemical-thermo dynamical liquid-vapor equilibrium theory. This paper describes fundamental spray and combustion characteristics of mixed fuel of B100 with lower boiling point fuels as well as the reformulation technique. By mixing lower boiling point fuel, lighter quality fuels can be refined. Thus, mixed fuels have higher volatility and lower viscosity. Therefore, vaporization of mixed fuel spray is promoted and liquid phase penetration of mixed fuel shortens as compared with that of neat BDF.
Technical Paper

Controlling PCCI Combustion with Mixed Fuel - Application of Flashing Spray to Early Injection

A diesel engine operating in premixed charge compression ignition (PCCI) mode promises the reduction of engine-out emissions of NOx and particulate matter. A serious issue for PCCI operation with the early injection timing during the compression stroke is the difficulty of controlling the mixture formation process. In this study, a mixed fuel consisting of high volatility fuel and high ignitability one is applied in order to develop a control technique for the mixture preparation. In particular, we focuses on a flash boiling phenomenon of mixed fuel. For pure substance, the quality of flashing spray is dominated by the degree of superheat. In contrast, that of mixed fuel is affected much by low boiling point fuel.
Technical Paper

Particulate Matter Emission in steady state operation and transient operation from Direct Injection (DI) Off-Road Diesel Engine

For protecting human health and preserving the clean environment, current regulations stipulate acceptable levels of particulate emissions based on the mass collected on filters obtained by sampling in diluted exhaust. Such regulations will be imposed not only on-road engines but also off-road engines. From the point of view of human health [1], so-called nano-particle (d<50nm) is thought to be nuisance because it could reach deeper lung tissue. So, many researches have been done in this research field [2]. A series of experiments were conducted on an off-road general purpose direct Injection (DI) diesel engine using EEPS (Engine Exhaust Particle Sizer) to make real time particle size distribution measurements possible. The data presented covers whole operating conditions including the operating modes of off-road diesel engine emission test (C1mode). Additionally, PM emissions in transient (NRTC test cycle) engine operation were examined.
Technical Paper

Instantaneous and Statistical Structures of Non-Evaporative Diesel Spray

Instantaneous and statistical spray structures of diesel sprays are examined with numerical simulation and experiment. KIVALES, which is LES version of KIVA code, is used as the computational code. Injection velocity profiles measured by momentum method are employed for the initial condition of the calculation. In the experiment, shadowgraph photography is performed to measure macroscopic spray structure. LES approach predicts the instantaneous structure, which are the heterogeneity and intermittency in the periphery of the spray and the cyclic variability of each injection event. Moreover, LES can predict both the instantaneous and statistical spray structures.
Technical Paper

Analysis of Fuel Flow and Spray Atomization in Slit Nozzle for Direct Injection SI Gasoline Engines

The slit nozzle in the fuel injection valve for a direct injection spark ignition gasoline engine forms a thin, fan-shaped spray. The fan-shaped spray is characterized by high dispersion, comparatively high penetration, and fine atomization. This enables it to form a stable air-fuel mixture. However, further improvement of engine performance requires that the spray characteristics (particularly the level of atomization) be improved. Since the spray characteristics are strongly influenced by the fuel flow within the nozzle, it was clarified this effect by visual analyses of the fuel flow inside the nozzle using enlarged acrylic slit nozzles. The results demonstrated that vortices that are formed within the nozzle sac are continuously propagated in a periodic manner within the sac and that they influence the streamline of fuel flow from the sac to the slit.
Technical Paper

Effect of Convective Schemes on LES of Fuel Spray by Use of KIVALES

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.
Technical Paper

Demonstrating the Potential of Mixture Distribution Control for Controlled Combustion and Emissions Reduction in Premixed Charge Compression Ignition Engines

The objective of this study is to explore the relation among mixture distribution condition, chemical character of fuel, combustion processes, and emissions characteristics with premixed charge compression ignition (PCCI) operation. The present experiment employs two fuel injectors which are capable of port injection and direct one. The former was used to supply a highly-homogeneous mixture and the latter with late injection timing was employed to control the mixture heterogeneity. Thus, these sets of injection equipments are capable of setting a wide variety of mixture heterogeneity. Furthermore, two primary reference fuels were used in order to know the influences of chemical character. The experiments were conducted in order to clarify the combustion and emissions characteristics through engine tests. Optical diagnostic was also performed to gain additional insight into the combustion processes for a wide variety of mixture distribution.
Technical Paper

OH Radical Generation and Soot Formation/Oxidation in DI Diesel Engine

OH radical generated in a DI diesel engine has a close relationship to soot oxidation. To clarify this fact, the distribution of the natural emission of OH radical was captured by means of an interference filter system and that of soot was detected by the simultaneous application of a laser induced incandescence (LB) and a laser induced scattering (LIS). The experiments were carried out in a small sized high-speed DI diesel engine installed with an optical access view. The generation of OH radical and the formation/oxidation of soot are discussed by using both images.
Technical Paper

Modeling Atomization and Vaporization Processes of Flash-Boiling Spray

Flash-boiling occurs when a fuel is injected to a combustion chamber where the ambient pressure is lower than the saturation pressure of the fuel. It has been known that flashing is a favorable mechanism for atomizing liquid fuels. On the other hand, alternative fuels, such as gaseous fuels and oxygenated fuels, are used to achieve low exhaust emissions in recent years. In general, most of these alternative fuels have high volatility and flash-boiling takes place easily in fuel spray, when they are injected into the combustion chamber of an internal combustion engine under high pressure. In addition, fuel design concept the multicomponent fuel with high and low volatility fuels has been proposed in the previous study in order to control the spray and combustion processes in internal combustion engine. It is found that the multicomponent fuel produce flash-boiling with an increase in the initial fuel temperature.