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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.

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.

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.

Selected as an alternative diesel fuel based on consideration regarding the relationship between the fuel molecular structure and exhaust emission and criteria as alternative fuels, Dimethylacetal (DMA) was evaluated in both a direct injection (DI) diesel and a Direct Fuel Injection Impingement Diffusion Combustion Diesel (OSKA-D) engines. Since DMA with a 1% commercial-type cetane improver has 53 for the cetane number, no ignition-assist divice such as a spark plug is needed, unlike methanol. According to the DI diesel engine test, the NOx emission for DMA was almost equal to that for hydrocarbon diesel fuel, but smoke for DMA was much lower than that for diesel fuel. The OSKA-D engine test showed that NOx emission for DMA was much lower than that for diesel fuel and smoke emission for DMA was zero under all engine conditions.

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 direct injection stratified charge engine using New Mixture Formation Technology (OSKA) has been developed. Experiments on a single cylinder engine, with methanol and gasoline fuels showed the following results: 1) With methanol, the maximum IMEP was 1.3 MPa and the best indicated thermal efficiency was 46 %. 2) With gasoline, the maximum IMEP was 1.16 MPa and the best indicated thermal efficiency was 43 %. Analysis of the cylinder pressure diagram showed the following results: 1) High indicated thermal efficiency was observed by low time loss. 2) A relatively short combustion duration was observed even if the engine was operated with an overall lean fuel-air mixture in the part-load condition. This fact suggests that a stratified charge was attained. 3) From observation of the heat release rate,it will be predicted that combustion is characterized by flame propagation.

The mixture formation by fuel spray impingement (OSKA system) was applied to a small direct-injection diesel engine in order to reduce the wall quenching- induced emissions, i.e., the emissions of THC and soluble organic fractions (SOF). Experiments were carried out using a single-cylinder engine, fitted with various piston cavity geometries, ran under a wide range of compression ratios and fuel injection specifications. The piston cavity was designed as a centrally located reentrant type. The combination of the high squish flow and the weak penetration of the OSKA spray was very effective in reducing harmful emissions. A short ignition delay, under the retarded fuel injection timing, was obtained because of the high compression ratio. The OSKA DI diesel engine showed reduced NOx, smoke, and THC emissions without deterioration of the fuel consumption compared to modern DI diesel engines used in automotive applications.

The effects of the spray impinging part on the in-cylinder airflow were numerically analyzed in the combustion chamber of the impinging diffusion direct injection diesel engine using KIVA-3 code. KIVA-3 code was enhanced to cater the impinging part as an internal obstacle by adopting the virtual droplet method, which is relatively easy to implement. Numerical result shows that the turbulence generation is promoted by the impinging part and is transformed by the squish flow into the piston cavity. The secondary flow is generated beneath the impinging part as well. The secondary flow area increases as the distance between top surface of the impinging part and bottom surface of the cylinder cover increases.

The new type of Diesel combustion engine has been developed. The new Idea Incorporates an impingement part in the central piston cavity. The fuel jet is injected against the impingement part, spreads and form fuel-air mixture. Single hole fuel injection nozzle is used and the relatively low opening pressure is needed. Intake air swirl is not needed. The re-entrant type combustion chamber is employed to get a relatively strong squish speed. Experimental with single cylinder 4 stroke prototype test engine showed that the brake mean effective pressure was 0.82 MPa and the maximum net specific fuel consumption was 220 g/kW.h. The NOx and smoke emissions was reduced compared with the conventional DI Diesel engine. The authors have developed a new type of Direct Injection Stratified Charge SI engine called “Direct Fuel Injection Impingement Diffusion Stratified Charge System” (hereafter called OSKA).

As a fundamental work on Direct Injection Impinging Diffusion Combustion Engine, fuel spray was injected momentary into a pressured CO2 gas and impinged onto a projection on a wall. Instantaneous photograph was taken and analyzed to clarify the spray characteristics. Nozzle opening pressure was varied to clarify its effects on spray characteristics. Nozzle needle was cut to form two pairs of flats on needle surface instead of its cylindrical one. The effect of this needle shape was also studied. Opening pressure of injection nozzle has produced very little effect on the spray tip penetration. Spray thickness is larger when needle opening pressure of injection nozzle is high. Spray tip penetration and spray thickness have become large when widths across flats is narrow.

This study is concerned with development of a new type of Diesel engine by impingement of fuel jet. The impinging part is installed on the cylinder head (OSKA-DH), against which the fuel jet is injected to spread and form fuel-air mixture. As a fundamental study on the mixture formation process, the observation of the impinged fuel jet was studied by using a pressurized vessel. High-speed combustion photographs of the OSKA and DI Diesel engine were also taken by using the experimental transparent engine. A single cylinder 4 stroke cycle prototype OSKA-DH engine (ø 118 x 108 mm) was developed. Pintle type single hole fuel injector is used and relatively low opening pressure of 15.3 MPa is employed. The re-entrant type combustion chamber and relatively high compression ratio of 20.4: 1 are employed. Experiments with a single cylinder proto-type engine showed that the lower NOx and smoke emissions compared with the conventional DI diesel engine.

This study is concerned with development of a new type of diesel engine using the fuel jet impingement (OSKA-DH). Simultaneous reduction of the NOx and smoke emission were demonstrated with single cylinder prototype OSKA-DH engine. As a fundamental study on the mixture formation process, the observation of impinged fuel spray was studied by using a pressurized constant volume vessel. The high-speed combustion photographs of both re-entrant and open type combustion chamber were also taken by using the experimental transparent engine. From the observation of pressurized vessel and high-speed combustion photographs, the mixture formation and combustion was strongly affected by the squish flow velocity. The short ignition delay and faster combustion were observed by the re-entrant type combustion chamber because of high squish speed.

A new mixture formation and combustion process for reducing both emissions and fuel consumption has been developed, where the fuel impinges onto the impinging surface and spreads into the free space, named the OSKA process. A single cylinder engine particulate emission test was conducted with full flow dilution tunnel. The OSKA process shows lower TPM (total particulate matter) emission than the conventional DI diesel at the corresponding operating condition. ISF(insoluble fractions) and SOF(soluble organic fraction) are lower than DI diesel's. Correlation between SOF and THC of OSKA engine is, however different from that of conventional DI diesel. OSKA emits lower THC than conventional DI diesel does at the same SOF emission. This is because the wall quenching effect is smaller in OSKA than in conventional DI diesel. A NEW MIXTURE FORMATION and combustion technology, impinging diffusion one named OSKA, has been developed by the authors.

The OSKA-DH diesel engine employed a unique system (hereafter called OSKA system) which is composed of a single-hole fuel injector, an impinging disk and a re-entrant type combustion chamber. This study is concerned with the combustion observation of both OSKA-DH diesel engine and conventional DI diesel engine by the high-speed photography and video system. This video system enables us to take combustion photographs under the warm-up condition of the engine. From the observation of those photographs, the OSKA-DH engine shows the shorter ignition delay compared with a DI diesel engine and the combustion flame of OSKA-DH diesel engine are concentrated in the center of the combustion chamber and a relatively monotonous flame intensity are observed. THE AUTHORS HAVE DEVELOPED a new type of Direct Injection Stratified Charge Engine called “Direct Fuel Injection Impingement Diffusion Stratified Charge System” (hereafter called OSKA System).

The new idea incorporates an impinging part in the central piston cavity. A relatively low injection pressure, lower than that of a conventional IDI Diesel engine, and a single hole fuel nozzle are used. The fuel spray is injected against the impinging part, spreads and forms a fuel-air mixture. Since a comparatively rich fuel-air mixture always stays around the impinging part and ignition is accomplished near the center of the mixture, steady, instantaneous and high-speed combustion is possible. As the fuel-air mixture is formed mostly in the cavity, there is little fuel in the squish area. Therefore, it is possible to prevent end-gas knocking, and in spite of the use of spark ignition, to employ a higher compression ratio than that of the conventional premixed SI engine. Experiments with a single cylinder prototype (4-stroke cycle) engine with gasoline fuel showed that the maximum BMEP was 1.0 MPa and the maximum brake thermal efficiency was 37.7 % (217 g/kW.h).

A new type of internal combustion engine has been developed. The new idea incorporates an impinging part in the central piston cavity. The fuel spray is injected against the impinging area, spreads and forms a fuel mixture. Since a comparatively rich fuel mixture always stays around the impinging part and ignition is acomplished at the center of the rich fuel mixture, steady, instantaneous and high-speed combustion is possible. As the fuel mixture is always formed in the cavity, there is little fuel in the squish area. Therefore, it is possible to prevent end-gas knocking, and in spite of the use of spark ignition, to operate the engine at higher compression ratio than a conventional premixed SI engine. Experiments with methanol fuel showed that BMEP was 1.1MPa and the maximum brake thermal efficiency was 42%. The combustion noise was lower than that of diesel engine. Brief tests with gasoline showed a maximum brake thermal effiency of 36%.

Ethanol is a promising alternative to fossil fuels because it can be made from biomass resources that are renewable. In the most cases, however, ethanol is blended with conventional fuels because of the limited amount of production. Ethanol-fuel blends are typically azeotropic and have a unique characteristic in vapor pressure and phase equilibrium, which is different from that of blends composed of simple aliphatic hydrocarbons. The current studies by the authors have developed a numerical vaporization model for ethanol-gasoline blends, which takes into account vapor-liquid equilibrium of azeotrope and high latent heat of vaporization of ethanol, in order to update the authors' multicomponent fuel spray model and to investigate effects of blending ethanol on droplet vaporization processes. In this paper, the developed vaporization model was validated through a comparison with experimentally-observed vaporization rate for single droplets of ethanol-n-heptane blends.

Effects of chemical reaction characteristics of premixed fuel were experimentally studied in a dual fuel compression ignition engine using port injection (PI) of gasoline-like component and direct injection (DI) of diesel fuel. Octane number of port injection fuels, direct injection timing and injection amount ratio between PI and DI were swept to assess the interaction between chemical reaction and mixture distribution in a combustion chamber. Chemical kinetic study using multi-zone modeling was also performed in order to explain experimental results under quiescent condition.