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Computational Fluid Dynamics (CFD) simulation is widely used in the development and validation of automotive engine performance. In engine simulation, spray breakup submodels are important because spray atomization has a significant influence on mixture formation and the combustion process. However, no breakup models have been developed for the fuel spray with plate-type multi-hole nozzle installed in port fuel injection spark ignition (SI) engines. Therefore, the purpose of this study is to simulate spray formation in port fuel injection precisely. The authors proposed the heterogeneous sheet breakup model for gasoline spray injected from plate type multi-hole nozzle. The novel breakup model was developed by clarifying the phenomenological mechanism of the spray atomization process. In this paper, this model was improved in dispersion characteristics and evaluated by the comparison of the model calculation results with experimental data.

In this study, the authors analyze the concentration distribution of an evaporative spray mixture with LIEF (Laser induced exciplex fluorescence) method, which is a type of optical measurement. LIEF method is one of the optical measurements for obtaining the spray concentration distribution for separating vapor/liquid phases based on the fluorescence characteristics. In this paper, a quantitative concentration distribution analysis method for wall impingement spray in heterogeneous temperature field has been proposed. Then, a series of experiments were performed in varying injection pressure and ambient density. As a result, a two-dimensional concentration distribution was obtained for the free spray and wall impingement spray.

Fuel design concept has been proposed for low emission and combustion control in engine systems. In this concept, the multicomponent fuels, which are mixed with a high volatility fuel (gasoline or gaseous fuel components) and a low volatility fuel (gas oil or fuel oil components), are used for artificial control of fuel properties. In addition, these multicomponent fuels can easily lead to flash boiling which promote atomization and vaporization in the spray process. In order to understand atomization and vaporization process of multicomponent fuels in detail, the model for flash boiling spray of multicomponent fuel have been constructed and implemented into KIVA3V rel.2. This model considers the detailed physical properties and evaporation process of multicomponent fuel and the bubble nucleation, growth and disruption in a nozzle orifice and injected fuel droplets.

We have proposed the application of Exhaust Gas Recirculation (EGR) gas dissolved fuel which might improve spray atomization through effervescent atomization instead of high injection pressure. Since EGR gas is included in the spray of EGR gas dissolved fuel, it directly contributes to combustion, and the further reduction of NOx emissions is expected rather than the conventional external EGR. In our research, since highly contained in the exhaust gas and highly soluble in the fuel, CO2 was selected as the dissolved gas to simulate EGR gas dissolved. In this paper, the purpose is to evaluate the influence of the application of CO2 gas dissolved fuel on the combustion characteristics and emission characteristics inside the single cylinder, direct injection diesel engine. As a result, by use of the fuel, smoke was reduced by about 50 to 70%, but NOx reduction does not have enough effect.

In previous study, the model for flash-boiling spray of multicomponent fuel was constructed and was implemented into KIVA code. This model considered the detailed physical properties and evaporation process of multicomponent fuel and the bubble nucleation, growth and disruption in a nozzle orifice and injected fuel droplets. These numerical results using this model were compared with experimental data which were obtained in the previous study using a constant volume vessel. The spray characteristics from numerical simulation qualitatively showed good agreement with the experimental results. Especially, it was confirmed from both the numerical and experimental data that flash-boiling effectively accelerated the atomization and vaporization of fuel droplets. However, in this previous study, injection pressure was very low (up to 15 MPa), and the spray characteristics of high pressure injection could not be analyzed.

We have proposed the application of EGR gas dissolved fuel which might improve spray atomization through effervescent atomization instead of high injection pressure. In this paper, the purpose is to evaluate the influence of the application of CO2 gas dissolved fuel on the combustion characteristics and emissions inside the single cylinder, direct injection diesel engine. As a result, by use of the fuel, smoke was reduced by about 50 to 70%. The amount of NOx was reduced at IMEP=0.3 MPa, but it was increased at IMEP=0.9 MPa.

In-cylinder total sampling technique utilizing a single-cylinder diesel engine equipped with hydraulic valve actuation system has been developed. In this study, particulate matter (PM) included in the in-cylinder sample gas was collected on a quartz filter, and the polycyclic-aromatic hydrocarbons (PAHs) component and soot were subsequently quantified by thermal desorption-gas chromatograph mass spectrometry (TD-GCMS) and a carbon analyzer, respectively. Cylinder-averaged histories of PAHs and soot were obtained by changing the sampling timing. It was found that decreasing intake oxygen concentration suppresses in-cylinder soot oxidation, and the fuel with higher aromatic and naphthenic contents accelerates soot production.

The CO2 gas dissolved fuel for the diesel combustion is effective to reduce the NOx emissions to achieve the internal EGR (Exhaust Gas Recirculation) effect by fuel. This method has supplied EGR gas to the fuel side instead of supply EGR gas to the intake gas side. The fuel has followed specific characteristics for the diesel combustion. When the fuel is injected into the chamber in low pressure, this CO2 gas is separated from the fuel spray. The distribution characteristics of the spray are improved and the improvement of the thermal efficiency by reduction heat loss in the combustion chamber wall, and reduce soot emissions by the lean combustion is expected. Furthermore, this CO2 gas decreases the flame temperature. Further, it is anticipated to reduce NOx emissions by the spray internal EGR effect.

Homogeneous Charge Compression Ignition (HCCI) combustion has attracted widespread interest as a combustion system that offers the advantages of high efficiency and low exhaust emissions. However, it is difficult to control the ignition timing in an HCCI combustion system owing to the lack of a physical means of initiating ignition like the spark plug in a gasoline engine or fuel injection in a diesel engine. Moreover, because the mixture ignites simultaneously at multiple locations in the cylinder, it produces an enormous amount of heat in a short period of time, which causes greater engine noise, abnormal combustion and other problems in the high load region. The purpose of this study was to expand the region of stable HCCI engine operation by finding a solution to these issues of HCCI combustion.

Internal combustion engines today are required to achieve even higher efficiency and cleaner exhaust emissions. Currently, research interest is focused on premixed compression ignition (Homogeneous Charge Compression Ignition, HCCI) combustion. However, HCCI engines have no physical means of initiating ignition such as a spark plug or the fuel injection timing and quantity. Therefore, it is difficult to control the ignition timing. In addition, combustion occurs simultaneously at multiple sites in the combustion chamber. As a result, combustion takes place extremely rapidly especially in the high load region. That makes it difficult for the engine to operate stably at high loads. This study focused on the fuel composition as a possible means to solve these problems. The effect of using fuel blends on the HCCI operating region and combustion characteristics was investigated using a single-cylinder test engine.

To execute the computational fluid dynamics coupling with fuel chemistry in internal combustion engines, simplified chemical kinetic models which capture the low-temperature oxidation kinetics would be required. A steady-state analysis was applied to see the complicated reaction mechanism of alkylperoxy radicals by assuming the steady state for hydroperoxyalkyl (QOOH) and hydroperoxyalkylperoxy (OOQOOH) radicals. This analysis clearly shows the systematic trend of the reaction rate for the chain-branching and non-branching process of alkylperoxy (ROO) radicals as a function of the chain length and the carbon class. These trends make it possible to classify alkylperoxy radicals by their chemical structures, and suggest a reduced low-temperature oxidation chemistry.

Fuel design approach has been proposed as the control technique of spray and combustion processes in diesel engine to improve thermal efficiency and reduce exhaust emissions. In order to kwow if this approach is capable of controlling spray flame structure and interaction between the flame and a combustion chamber wall, the present study investigated ignition and flame characteristics of dual-component fuels, while varying mixing fraction, fuel temperature and ambient conditions. Those characteristics were evaluated through chemiluminescence photography and luminous flame photography. OH radical images and visible luminous flame images were analyzed to reveal flame shape aspect ratio and its fractal dimension.

One of the authors has proposed to use the decay rate of EHRR, the effective heat release rate, d2Q/dθ2 as an index for the rapid local combustion [1]. In this study, EHRR profiles and the cylinder gas pressure oscillations of the low and high speed knock are analyzed by using this index. A delayed rapid local combustion, such as an autoignition with small burned mass fraction can be detected. In the cases of the low speed knock, it has been agreed that a rapid local combustion is an autoignition. Although whether the cylinder gas oscillation is provoked by an auto ignition in a certain cycle or not is an irregular phenomenon, the auto ignition takes place in almost all of the cycles in the knocking condition. Mixture mass fraction burned by an auto ignition is large. A small auto ignition may induce a secondary auto ignition, in many cases, mass burned by the secondary auto ignition is extremely large.

The compressible Large-Eddy Simulation (LES) for the diesel spray with OpenFOAM is presented to reduce CPU time by massively parallel computing of the scalar type supercomputer (CRAY XE6) and simulate the development of the non-evaporative and the evaporative spray. The maximum computational speeds are 14 times (128 cores) and 43 times (128 cores) for of the non-evaporative spray and the spray flame with one-step reaction, respectively, compared to the one core simulation. In the spray flame simulation with the reduced reaction mechanism (29 species, 52 reactions), the maximum computational speed is 149 times (512 cores). Then LES of the non-evaporative and the evaporative spray (Spray A) are calculated. The results indicate that the spray tip penetration is well predicted, although the size of the computational domain must be set equal to that of the experiment.

The ignition characteristics of each component of natural gas and the chemical kinetic factors determining those characteristics were investigated using detailed chemical kinetic calculations. Ethane (C2H6) showed a relatively short ignition delay time with high initial temperature; the heat release profile was slow in the early stage of the ignition process and rapid during the late stage. Furthermore, the ignition delay time of C2H6 showed very low dependence on O2 concentration. In the ignition process of C2H6, HO2 is generated effectively by several reaction paths, and H2O2 is generated from HO2 and accumulated with a higher concentration, which promotes the OH formation rate of H2O2 (+ M) = OH + OH (+ M). The ignition characteristics for C2H6 can be explained by H2O2 decomposition governing OH formation at any initial temperature.

The interaction between spark discharge and low-temperature oxidation (LTO) was investigated using an optical compression and expansion machine fueled with n-C7H16 or i-C8H18 for an equivalence ratio of 0.33. Charge pressure was adjusted so that the compression stoke could induce LTO for n-C7H16, but could not lead to high-temperature reactions. A spark was discharged in the field before, during, or after the LTO for n-C7H16 or in the field without LTO for i-C8H18. Reaction zones were induced in the field after the LTO, whereas no reaction zones were induced in the fields before the LTO and without LTO. Local ignitions were induced in the areas surrounding the propagating reaction zones. The reaction zone propagation with the low equivalence ratio must be a different phenomenon from conventional flame propagation. The reaction zones can compress or heat the surrounding areas containing H2O2 and CH2O, and accelerate an H2O2 regeneration loop in the pre-reaction zones.

Homogeneous Charge Compression Ignition (HCCI) has attracted a great deal of interest as a combustion system for internal combustion engines because it achieves high efficiency and clean exhaust emissions. However, HCCI combustion has several issues that remain to be solved. For example, it is difficult to control engine operation because there is no physical means of inducing ignition. Another issue is the rapid rate of heat release because ignition of the mixture occurs simultaneously at multiple places in the cylinder. The results of previous investigations have shown that the use of a blended fuel of DME and propane was observed that the overall combustion process was delayed, with that combustion became steep when injected propane much. This study focused on expanding the region of stable engine operation and improving thermal efficiency by using supercharging and blended fuels. The purpose of using supercharging were in order to moderated combustion.

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.

Ignition process chemistry was analyzed using a detailed chemical kinetic model of n-heptane generated by KUCRS (Knowledge-basing Utilities for Complex Reaction Systems), wherein pressure-dependent rate constants of the O₂ addition to alkyl radicals and hydroperoxy alkyl radicals and the thermal decomposition of ketohydroperoxides have been introduced. Then, the effect of the initial pressure and the individual effects of the initial fuel, O₂ and N₂ molar concentrations on a relationship between the initial temperature and the ignition delay were discussed. When the initial temperature increases, the branch of C₇H₁₄OOH removal into the second O₂ addition and the decomposition into C₇H₁₄cyO and OH is more sensitive to the pressure and the O₂ concentration, and thus, the LTO preparation phase is more affected by the pressure and the O₂ concentration. The LTO phase terminates mainly by the OH removal by intermediate species.

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.