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This paper proposes a new mixing-controlled, low temperature combustion (LTC) approach for high-speed direct injection (HSDI) diesel engines. The purpose of this approach is to avoid the excessively high pressure-rise rate (PRR) of premixed, kinetics-controlled LTC and to enable the low nitrogen oxides (NOx) combustion to operate over the wide speed and load range of the engine. To address the soot/noise trade-off at high load LTC operating conditions, the pressure modulated multiple-injection coupled with swirl control was applied. This injection strategy enables the injection of high pressure (HP) main spray into the local high temperature region of the already burning low pressure (LP) pilot spray injected from the neighboring injection hole. By employing this injection strategy, the equivalence ratio (φ) distribution of mixture is drastically varied during main combustion processes.

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.

In a high-speed DI diesel engine, fuel sprays impinge surely on a wall of a piston cavity. Then the phenomenon of the heat transfer between the impinged spray and the wall appears and it has the strong effect on the combustion processes of the engine. The purpose of this study are to clarify basically the heat transfer characteristics. In the experiments, the fuel was injected into the quiescent inert atmosphere with a high temperature under high pressure field, and an evaporative single diesel spray was impinging upon a flat wall. And, the temperature distribution on the wall surface in a radial direction was detected by the Loex-Constantan thin film thermo-couples. Thus, the heat flux between the impinged spray and the wall surface was calculated from the temperature profile within the wall by Fourier's equation using the finite difference method, under the assumption of the one-dimensional heat conduction.

Some papers on the combustion in a diesel engine have been already presented to discuss the effect of the additive called ADOIL TAC. A bottom view DI diesel engine driven at 980rpm with no load was used in the experiment presented here, in order to make clear this effect. JIS second class light diesel fuel oil was injected through a hole nozzle at the normal test run. The additive was intermixed 0.01 vol. % in this fuel oil, in the experiments to compare with the normal combustion. The flame was taken by direct high-speed photography. Profiles of flame temperature and KL were detected on the film by image processing, applying the two-color method. Soot was visualized by high-speed laser shadowgraphy, and the heat release rate was calculated using the cylinder pressure diagram. Discussion on the effect of the additive on the combustion phenomena was made by using all the data.

Authors have experimented the effects of cooling water temperature on the particulate emission characteristics from a high speed DI diesel engines. A single cylinder small high speed DI diesel engine is operated under various engine speed and load conditions. Cooling water temperature is varied from 313 K (40 °C) to 363 K (90 °C). Particulate is collected using a single stage full size dilution tunnel. Dry soot and SOF emissions are measured, as well as total particulate. SOF increases when the cooling water temperature decreases, as well as HC increases. SOF also increases as load decreases. This suggests that the SOF emits at the cold starting and warming up periods. This also suggests that the SOF can be reduced by increasing cooling water temperature. IT IS IMPORTANT TO CLARIFY the effects of cooling water temperature on the particulate emission.

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.

In the urea SCR system, urea solution is injected by injector installed in the front stage of the SCR catalyst, and NOx can be purified on the SCR catalyst by using NH3 generated by the chemical reaction of urea. NH3 is produced by thermolysis of urea and hydrolysis of isocyanic acid after evaporation of water in the urea solution. But, biuret and cyanuric acid which may cause deposit are sometimes generated by the chemical reactions without generating NH3. Spray behavior and chemical reaction of urea solution injected into the tail-pipe are complicated. The purpose of this study is to reveal the spray behavior and NH3 generation process in the tail-pipe, and to construct the model capable of predicting those accurately. In this report, the impingement spray behavior is clarified by scattered light method in high temperature flow field. Liquid film adhering to the wall and deposit generated after evaporation of water from the liquid film are photographed by the digital camera.

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.

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.

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.

This paper is concerned with the formation of Particulate Matter (PM) in direct-injection (DI) diesel engines. A system featuring an electromagnetically actuated sampling valve was used for sampling of gas directly from the combustion chamber. The concentrations of total particulate matter (TPM) and of its two components, the Soluble Organic Fractions (SOF) and the Insoluble Fractions (ISF), were determined at different locations in the combustion chamber at different sampling times (different crank angles). High concentrations of SOF were found at sampling positions along the spray flame axis. The concentrations of SOF and ISF were higher at sampling positions close to the wall than away from the wall. The results suggest that SOF formation is significantly affected by wall quenching. Also, the PM concentrations were much higher in the combustion chamber than in the exhaust.

CNG is one of the future fuel for a CI engine. Recently, the general tendency is the use of the high pressure injection system over 100 MPa in a CI engine for the near future severe regulation. Combustion phenomenon in a CI engine with such injection system is like a transient gas diffusion flame. The flow in a gas diffusion flame was investigated by the particle image velocimetry on its 2-D images, the relative soot concentration, the temperature and the relative CO2 concentration was detected in the experiments. And the model of transient gas diffusion flame was constructed by use of experimental data.

A low emission and high combustion load combustor is developed. The combustor reduces both NOx and unburnt fractions using rich-lean staged combustion. NOx is suppressed by fuel-rich combustion in the primary combustion chamber. Unburnt fraction is oxidized by the transition from rich to lean combustion. To avoid NOx formation, residence time nearby stoichiometry is shortened. NOx is less than 24.8 ppm(16 % O2 equivalence) or 2.26 g/kg throughout the experiments. Combustion efficiency is high regardless of the wide operating range. Specific combustion load is up to 33.6 MW/m3 without excessive NOx emission under atmospheric air condition.

The surroundings around the diesel spray are entrained during the growth of the spray. The mixing process between the evaporated fuel oil and the entrained surroundings, that is, the entrainment, has a significant meaning for the combustion diesel engine. It is difficult to detect the movement of the entrainment because the diesel spray is the gas-liquid two-phase flow and the unsteady phenomenon within a few milliseconds. Then, in order to clarify and to generalize the movement of entrainment, following three experiments were done. 1)Two-dimensional steady water spray -flat spray- injected into the ambient atmosphere, using tuft and hot wire method. 2) Unsteady water jet injected into water, using tracer. 3)single diesel spray injected into the atmosphere with high pressure at room temperature, using smoke wire.

The process of forming mixtures of injected fuels and ambient air has significant effects on the ignition and combustion process in the direct injection engine. In these engines fuel is injected intermittently and fuel jet impinges on a combustion chamber wall. This study deals with a fundamental experiment on the mixing process of the transient gas jet together with the instantaneous concentration measurement and statistical analysis of the transient turbulent mixing process in the jet. Helium or carbon dioxide is injected at constant pressure into quiescent atmosphere through the single shot device. This paper presents a laboratory automation system for measuring the characteristics of transient gas jet and processing the data. A discussion on the process of mixture formation of transient gas jets impinging on a wall is carried out with time- and space- resolved concentration distribution.

This paper presents a fundamental study on the mixture formation process in a direct injection stratified charge (DISC) engine. Helium is injected intermittently and impinged on a wall to clarify the unsteady wall impinging jet. Instantaneous concentration and pressure distributions are obtained by using fast-response concentration and pressure probes, respectively. The jet tip rolls up after the impingement on the wall, consequently the volume of an unsteady wall impinging jet becomes larger than that of a steady wall impinging jet. Wall impingement increases air entrainment, which could promote faster combustion in DISC engines.

The mixture formation process plays an important role on combustion in the direct injection stratified charge engine. A new mixture formation technology named OSKA has been developed for direct injection stratified charge SI engines. The OSKA process has the potential to yield better fuel economy and cleaner emissions. However, the mixture formation process has not been clarified completely, and detailed studies of the mixture formation process with the OSKA technology are needed. As a fundamental study on the OSKA mixture formation, time and space resolved distribution is obtained on concentration and on pressure in the unsteady gas jet, which discharges with constant injection pressure into a quiescent atmosphere and impinges on a projection placed on a wall.

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.

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.

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.