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In this study, we evaluated NOx production rates of diesel combustions occurred in a constant volume chamber of a rapid compression machine in order to investigate relationship between flame behaviors and NOx emissions. A total gas sampling device was used to measure the NOx concentration in total gases existing in the chamber at a designated time. An EINOx (Emission Index of NOx) production rate was evaluated on the time history of NOx concentration. Temporal temperature distributions in the chamber were measured with a high speed 2-color thermometry. Gas oil (JIS #2) was used as the fuel. The EINOx production rate increases with increasing injection pressure through temperature rises in flames due to enhanced mixing of fuel vapor with ambient air. An increase in the ambient pressure causes overlaps between flames formed around the nozzle, which reduces the flame temperature.

Spray development and fuel-air mixture formation are important process early in diesel combustion. Moreover, wall impingement of spray and spray interaction also affect combustion process greatly. The spray interaction happens in multi-hole injector. This study investigated influence of spray combustion accompanied with wall impingement and spray interaction on heat release history. The experiment observed initial spray development by shadowgraph technique using a constant volume spray chamber. The injectors were a single-hole injector and multi-hole injectors with the hole-number of 8, 6 and 4. The combustion experiment observed flame development. The spatial distribution of the flame temperature and the soot oxidation were analyzed by the flame images. Results of the unburned spray images revealed the difference of mixture formation and initial combustion between single-hole and multi-hole sprays.

It is widely known that direct application of biomass fuels oil to DI diesel engines increases the carbon deposit in the engine. To minimize this effect, biomass fuel is subjected to transesterification process. Nevertheless, it is still desirable to use biomass fuel without transesterification. As diesel engine combustion and emissions are strongly dependent on spray characteristics and mixture formation, this study tries to clarify the spray characteristics of rape-seed oil (SVO) including spray structure, spray development, fuel evaporation, and droplets atomization. Optical observation reveals that rape-seed oil (SVO) spray forms a stick-like structure without branching structure at spray boundary and has heterogeneous density distribution in a liquid column at spray centerline. SVO spray hardly penetrates at exceedingly initial stage of injection, in particular at low injection pressure.

Hydrogen engines have problems of knocking, lower thermal efficiency and NOX emission. These problems are caused by the hydrogen characteristics of high burning velocity. This study tried to reduce rapid combustion of hydrogen. Hydrogen was injected directly into the combustion chamber and the hydrogen-jet was ignited by a spark plug. Moreover, this kind of combustion system was applied to a newly developed engine employing Z-crankshaft mechanism. This mechanism can realize a quasi-constant volumetric cycle. In the result, the engine realizes knock-less combustion with low NOX emission. In addition, Z-crankshaft engine can keep high thermal efficiency even at late ignition timing.

Diesel spray evaporation in a high pressure and high ambient temperature close to actual diesel engine condition was investigated in this study. A nano-spark shadowgraph photography technique and a rapid compression machine were applied in this experiment. By using this method, relatively clear image of liquid phase, vapor phase and droplets was obtained. In order to quantify the spray characteristics in the spray liquid area and vapor phase area, an image analysis method was applied. An algorithm was developed to quantify the droplets size and number of the droplets characteristic in the vapor phase. Experimental results have revealed that the injection pressure and the ambient temperature do not affect the spray penetration length apparently. In the case of ambient temperature Ti = 700K, the liquid core is observed in the region near the spray axis. Meanwhile, the vapor exists mostly in the outer region in the middle of the spray.

This study investigates the effect of using waste cooking oil (WCO) and Bio-diesel Fuel (BDF) of WCO on combustion performance and exhaust emissions compared with diesel fuel (JIS#2) in a direct injection diesel engine. Results show that WCO and BDF emit higher concentration of SOF at low load compared with JIS#2. A study on blending WCO and BDF with several percentage of JIS#2 reveals that reduction of kinematic viscosity would be able to improve SOF emissions at low load. SOF emission also can be reduced by using high squish combustion chamber which continues high turbulence combustion in the chamber.

The objective of this investigation is to characterize the influence of injection parameters and spray-wall interaction on atomization and gas entrainment processes of high-pressure non-evaporative sprays injected into a high-pressure vessel using several imaging techniques. The effects of injection pressure on the droplet distribution, size and velocity were quantified using single and double nano second exposure photography techniques. A laser-sheet imaging method was employed to measure the two-dimensional gas velocity around the spray and to clarify the effects of the above parameters on the gas entrainment into the impinging sprays. It was found that increasing the injection pressure causes an increase in droplet number in both free and wall-jet regions of the sprays. Spray-wall impingement creates a large-scale gas vortex around the spray, which promotes the gas entrainment into sprays typically at the impinging zone, and it also affects the spatial distribution of droplets.

The aim of this study is to develop a plasma-assisted after-treatment system for simultaneous reduction of NOx and PM in diesel exhaust, which is less sensitive to the fuel sulfur. The work presented focuses on development of a high-frequency dielectric barrier discharge reactor for oxidation of NO to NO2 in diesel exhaust and low-temperature oxidation of diesel soot with NO2. The first part of this paper describes the combustion characteristics of carbonaceous matters with pure NO2 and discusses the difference when oxygen is used as oxidation agent. The second part focuses on the development of a high-frequency dielectric barrier plasma reactor and describes the effects of plasma reactor configuration, energy density and gas composition on the NO conversion into NO2, and last part describes the soot oxidation with the plasma gas. The results reveal that NO can be efficiently oxidized into NO2 using the developed plasma reactor.

Effects of water-emulsified fuel on diesel combustion and emission reduction process were investigated under various ambient temperatures, equivalence ratios and water addition ratios using a rapid compression machine and a total-gas sampling device. The results indicate that promoted diffusion combustion of emulsified fuels offers a shorter combustion duration and an increase in amount of heat release when compared with those of gas oil. NOx concentration decreases with increasing the water content in emulsion fuels. This reduction is due to low NO formation rate and short duration of NO formation. Laser extinction measurement of the in-chamber KL factor shows that soot oxidation is promoted for emulsified fuels during the diffusion combustion stage.

The aim of this study is to clarify the mixture formation in the combustion chamber of our developed natural gas engine incorporating the sub-chamber injection system, in which natural gas is directly injected into a combustion sub-chamber in order to completely separate rich mixture in the sub-chamber, suitable for ignition, from ultra-lean mixture in the main chamber. Mixture distributions in chambers with and without sub-chamber were numerically simulated at a variety of operating conditions. The commercial software of Fluent 16.0 was used to conduct simulations based on Reynolds averaged Navier-Stokes equations in an axial 2 dimensional numerical domain considering movements of piston. Non-reactive flow in the combustion chamber was simulated before the ignition timing at an engine speed of 2000 rpm. The turbulence model employed here is standard k-ε model. Air-fuel ratio is set with a lean condition of 30.

The mixture formation prior to the ignition process is a key element in the diesel combustion because it significantly influences throughout the combustion process and exhaust emissions. Purpose of this study is to clarify the effects of ambient temperature, oxygen concentration and air entrainment into the spray on the heat release process during ignition delay periods. This study investigated diesel combustion fundamentally using a rapid compression machine and high speed digital video camera. The detail behavior of spray evaporation, spray interference and mixture formation during ignition delay period was investigated using the schlieren photography system. Ignition process, flame development and images of the spray ignition with extremely dark flame were investigated by light sensitivity direct photography method. Heat release processes were analyzed by pressure measurement in the chamber.

It is well known that indirect injection (IDI) diesel engines have better exhaust performance but lower fuel economy than direct-injection (DI) diesel engines. In recent years, fuel efficiency has been strongly demanded to reduce global warming. Therefore, the IDI engine is required to reduce fuel consumption. According to past research, fuel injection control can be one of the means to improve fuel efficiency in the IDI system. This paper tried to apply two-stage fuel injection as one of the fuel injection control methods to improve fuel efficiency while suppressing exhaust emissions. Particularly, since it is considered necessary to reduce the amount of injection during the ignition delay period in the sub-chamber with the IDI type, two-stage injection with a small amount of pilot injection was applied.

The chemical behaviors of diesel fuel and the effects of aromatic content on combustion characteristics and NOx histories were experimentally investigated using a rapid compression machine and a total-gas sampling device. The aromatic content was changed under constant cetane number. Composition of the individual hydrocarbons, inorganic gases and NOx under various ambient temperatures and fuel injection pressures were analyzed with aromatic-free and aromatic-containing fuels. The results indicate that injected fuel is rapidly decomposed and dehydrogenated during the ignition delay period. The decomposed low boiling-point hydrocarbons consist of mainly unsaturated hydrocarbons such as C2H4, C2H2 and C3H6 at the initial combustion phase. At the diffusion combustion phase, the low boiling-point hydrocarbons consist of mainly CH4.

This study investigates the effects of fuel properties on combustion characteristics and emissions such as NOx, smoke, THC and particulates in a direct-injection diesel engine. Fuel properties, such as cetane number and aromatic content, are varied independently in the experiments to separate their effects. The engine tests are carried out at steady operation with changed load, injection timing and injection pressure. The results show that reducing cetane number results in the increase of NOx and decrease of particulate emission at high load. This is because the low cetane number fuel has the long ignition delay and causes the high maximum heat release rate and the short combustion duration. However, high THC emission is produced at low load for the low cetane number fuel.

In this study it is tried to reduce NOx and particulate emissions simultaneously in a direct injection diesel engine based on the concept of two-stage combustion. At initial combustion stage, NOx emission is reduced with fuel rich combustion. At diffusion combustion stage, particulate emission is reduced with high turbulence combustion. The high squish combustion chamber with reduced throat diameter is used to realize two-stage combustion. This combustion chamber is designed to produce strong squish that causes high turbulence. When throat diameter of the high squish combustion chamber is reduced to some extent, simultaneous reduction of NOx and particulate emissions is achieved with less deterioration of fuel consumption at retarded injection timing. Further reduction of NOx emission is realized by reducing the cavity volume of the high squish combustion chamber. Analysis by endoscopic high speed photography and CFD calculation describes the experimental results.

High boosting technology is commonly applied to diesel engines in recent years. Amid this trend, the study of spray behavior at ignition delay period still plays an important role in diesel combustion. This study focuses on the effect of ambient condition on diesel spray. The study investigates both macro-scale and micro-scale dynamic behaviors of diesel spray affected by ambient density and temperature at early stage of injection. A study via dual nano-spark shadowgraph method and rapid compression machine has been carried out to simulate real diesel engine combustion and to further understand the dynamics behavior of droplet evaporation and size distribution at early stage of mixture formation in the chamber. The micro-scale images captured reveal a shape variation of branch-like structures formed at the spray boundary. The evaporation of droplets is also captured clearly in macro- and micro scale photographs under the condition of high temperature ambient.

This study tries to reduce SOF (Soluble Organic Fraction) emissions at low load by improving spray characteristics of rape-seed oil and avoiding wall-impingement of the spray to the piston wall in a real direct-injection diesel engine applying rape-seed oil directly. High swirling air motion and squish flow caused by the piston configurations are taken as measures. Further, flat bottom shape of the piston is applied. Results show that emissions can be improved by the support of air motions. High swirl with toroidal piston is effective to reduce SOF emissions. Re-entrant piston with flat bottom shape offers the best emission performance. Raising gas temperature is also effective to reduce SOF emissions at low load.

Evolution of evaporating diesel spray is complex phenomena; however, it is important process for ignition, combustion and emission formation in diesel combustion. In this research, droplets evaporation process at spray boundary was experimentally investigated focusing on the behavior of evaporating droplets during ignition delay period. In the experiment, nano-spark shadowgraph photography technique was applied to a rapid compression machine. This study developed a new optical system to observe spray evaporation process. The existing systems can hardly analyze transitional behavior of vapor phase of spray and droplets behavior in high number-density region. The new technology that is named dual nano-spark shadowgraph photography method can record both macro-scale and micro-scale continuous spray images clearly at very short time interval of 15µsec on normal photographic black and white film.

Sub-chamber is a useful device with regard to sustaining stable operation of compressed natural gas (CNG) engines under lean burn conditions. In our previous studies, we applied a sub-chamber injection system to CNG engines, in which a single injector and a spark plug are mounted in a small sub-chamber. The aim of this study is to investigate the effect of the sub-chamber configuration on heat release in the main combustion chamber. 11 types of sub-chamber with different nozzle number, nozzle diameter, and sub-chamber volume were examined under a condition that pressure is 2.3 MPa, and global equivalence ratio is 0.6. When the sub-chamber with smaller nozzles are used, the penetration velocity of burned gas jet increases. In addition, the velocity also increases with an increasing sub-chamber volume. The high-speed penetration of burned gas jet shortens the period of initial flame development.

Many technologies for reducing exhaust emissions of wide variety of diesel engines from small size to large size ones have been considered with the improvement throughout the combustion process. To reduce emissions, mixing of fuel and air is still important phenomena. Purpose of this study is to clarify the relation between mixture formation during the ignition delay period and burning process in diesel combustion that strongly affects the exhaust emissions. In this study, a rapid compression machine was used to simulate actual phenomenon inside the combustion chamber with changing ambient density. In addition, swirl velocity and injection pressure were changed as experimental parameters to improve mixture formation at high ambient density. This study constructed schlieren photography system with a high-speed digital video camera to investigate the detail behavior of mixture formation during ignition delay period.