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In this study, characteristics of the development and auto-ignition/combustion of hydrogen jets were investigated in a constant-volume vessel. The authors focused on the effects of the jet developing process and thermodynamic states of the ambient gas on auto-ignition delays of hydrogen jets. The results show that the ambient gas temperature and nozzle-hole diameter are significantly effective parameters. By contrast, it is clarified that the ambient gas oxygen concentration has a weak effect on the auto-ignition/combustion of hydrogen jets. Consequently, it is supposed that the mixture formation process is capable of improving the auto-ignition/combustion of hydrogen jets.

Utilization of biofuels to vehicles is attracting attention globally from viewpoints of preventing global warming, effectively utilizing the resources, and achieving the local invigoration. Representative examples are bioethanol and biodiesel. This study highlights biodiesel and hydrotreated vegetable oil (HVO) in view of reducing greenhouse gas emission from heavy-duty diesel vehicles. Biodiesel is FAME obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. As already reported, FAME has fuel properties different from conventional diesel fuel, resulting in about 10% increase in NOx emission [1],[2],[3]. Suppression of such increase in the NOx emission during operating with biodiesel requires adjustment of the combustion control technology, such as fuel injection control and EGR, to the use of biodiesel.

The use of biofuel is essential for the reduction of greenhouse gas emission. This study highlights the use of biodiesel as a means of reducing greenhouse gas emission from the diesel engine of heavy-duty vehicles. Biodiesel is fatty acid methyl ester (FAME) obtained through ester exchange reaction by adding methanol to oil, such as rapeseed oil, soybean oil, palm oil, etc. The CO2 emission from combustion of biodiesel is defined to be equivalent to the CO2 volume absorbed by its raw materials or plants in their course of growth. On the other hand, however, operation of diesel engine with biodiesel is known to increase the NOx emission when compared with that with conventional diesel fuel. Then suppressing this NOx increase is regarded as a critical issue. This paper consists of two parts: comprehending the factors of NOx emission increase and improving this emission performance in a diesel engine fuelled with biodiesel.

A variable valve timing (VVT) mechanism was applied to achieve premixed diesel combustion at higher load for low emissions and high thermal efficiency in a light duty diesel engine. By means of late intake valve closing (LIVC), compressed gas temperatures near the top dead center are lowered, thereby preventing too early ignition and increasing ignition delay to enhance fuel-air mixing. The variability of effective compression ratio has significant potential for ignition timing control of conventional diesel fuel mixtures. At the same time, the expansion ratio is kept constant to ensure thermal efficiency. Combining the control of LIVC, EGR, supercharging systems and high-pressure fuel injection equipment can simultaneously reduce NOx and smoke. The NOx and smoke suppression mechanism in the premixed diesel combustion was analyzed using the 3D-CFD code combined with detailed chemistry.

One of the most effective means of improving the thermal efficiency and the specific fuel consumption in spark ignition engines is the increase of the compression ratio. However, there is a limit to it because of the generation of knocking combustion due to the rise of temperature and pressure in the unburnt mixture. Also in turbo charged spark ignition engines, the ignition timing cannot be advanced until MBT in order to avoid the knocking phenomena. Generally speaking, it is very difficult to investigate the phenomena in an actual engine, because there are many restriction and the phenomena are too complex and too fast. According-ly, it is advantageous to reveal the phenomena fundamentally, including the autoignition process of the end-gas by using simplified model equipment. Therefore, a rapid compression and expansion machine (RCEM) with a pan-cake combustion chamber was designed and developed for the experiments presented here.

In the direct injection spark ignition gasoline engine (D-4), thin fan-shaped high-dispersion, high-penetration and high-atomization spray formed by the slit nozzle generates a stratified mixture cloud without depending on a strong intake air motion, subsequently realizing stable stratified charge combustion. To improve fuel economy further in actual traffic, the region of stratified charge combustion in torque-engine speed map must be expanded by improving spray characteristics. Since the fuel flow inside the nozzle has a large effect on the spray characteristics, it was clarified this effect by visual analysis of the fuel flow inside the nozzle using an enlarged acrylic slit nozzle of 10 magnifications. Consequently, it was found that vortices are generated frequently within a sac even in the case of steady state conditions. The effect on the spray characteristics is corresponding to the vortex scale.

The 1997 Kyoto protocol came into effect in February, 2005 to reduce greenhouse gases within the period 2008-2012 by at least 5 % with respect to 1990 levels. Application of biodiesel fuel (BDF) to diesel engine is very effective to reduce CO2 emission, because BDF is carbon neutral in principle. The purpose of this project is to produce a light-duty biodiesel truck which can be suitable for emission regulation in next generation. The effect of BDF on the performance and emissions of modern diesel engine which was equipped with the aftertreatment for PM and NOx emissions was investigated without modifications of engine components and parameters, as a first step for research and development of biodiesel engine. Rapeseed oil methyl ester (RME) was selected in behalf of BDF, and combustion characteristics, engine performance and exhaust emissions were made a comparison between RME and petroleum diesel fuel by steady operation and Japan transient mode (JE05) tests.

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.

We propose a new concept on simultaneous reduction of NO and soot emissions in Diesel engine exhaust by the diesel fuel oil (n-Tridecane) with liquefied CO2 dissolved. The CO2 dissolved fuel is expected to undergo flash boiling or gas separation when being injected into the combustion chamber and improve spray atomization and mixing process both of which are primary factors to govern soot formation. Also the internal EGR effect caused by CO2 injected with the fuel is expected to NO formation. In order to assess this concept, combustion experiments were carried out using a rapid compression and expansion machine. Thus, flame characteristics and heat release rate were analyzed for the combustion process of diesel fuel and CO2 mixed fuel. And, it is revealed that the diesel fuel-liquefied CO2 mixed fuel can successfully reduce NO emission in a diesel combustion system.

There is a concept that the increase in the temperature of charge in a combustion chamber and the shield of heat transferred through a chamber wall can facilitate the oxidation of soot and reduce the discharge of soot from the engine. In the experiments presented here in, an IDI diesel engine was used to inspect the concept. The engine was installed a bigger sized cylindrical swirl chamber which was equipped with two flat quarts windows, in order to observe the combustion phenomena and to apply the optical measurement. The experiments were carried out using two types of divided chambers, that is, the swirl chamber made of ceramics and that made of steel, to examine the the effects mentioned above.

A transient gas jet seems to be a model of a diesel spray because it has no vaporization process. Recently, CNG is utilized in a diesel engine. In the case of diesel engine, sprays or jets have the free state in some cases, and they are impinging surely on the piston surface in the other cases. The 2-D image of acetylene gas with tracer particles was taken by high-speed photography. In both jets, the outer shape was measured on the images and the characteristics of the internal flow was obtained by particle image velocimetry. Then, the physical models of these jets were constructed by use of experimental results.

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.

For current passenger vehicles, multi-point injection (MPI) systems are extensively employed for gasoline engines due to ease of control and rapid response. In these systems, the pressure within the intake manifold to which the injectors are installed can fall below the saturated vapor pressure of some hydrocarbon components present in the fuel. Such a condition leads to an atomization process in which flash boiling occurs. In the present work, the atomization process under flash boiling conditions has been characterized both experimentally and theoretically. The experimental investigation has been carried out with a spray test facility consisting of a variable pressure chamber equipped with a pintle type fuel nozzle. Infrared Extinction/Scattering (IRES) is utilized to provide temporal and spatially resolved distribution of the fuel vapor concentration within the spray.

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.

It is unavoidable that a DI diesel engine exhausts a blue and white smoke at starting, especially in the cold atmosphere. In the experiments presented here, a small DI diesel engine started under the conditions of coolant and suction air whose minimum temperatures were 255 K and 268 K, respectively. The flame was photographed by high-speed photography, the temperature of flame and the soot concentration were measured by two-color method, and CO2 concentration was detected by luminous method. The engine cannot be started over several cycles when the coolant temperature is 255 K and suction air temperature is 268 K. As the temperature of coolant and suction air are decreasing, the maxima of the cylinder pressure, the flame temperature, the soot concentration and CO2 concentration are decreasing. Luminous small dots or small lumps of flame become scattered in the piston cavity.

Knocking phenomenon in a spark ignition engine breaks out due to autoignition in the unburned gas region. Investigation on the pre-autoignition reaction, that is, the reaction of cool and blue flames happening before autoignition must be carried out in detail to control knocking. The reactions appear in an extremely short time before autoignition, so, much difficulties accompany an attempt to grasp the situation. In the experiments presented hear, progress situation of pre-autoignition reaction was made clear by visualized phenomena in a rapid compression and expansion machine (R.C.E.M), which had good reproducibility. Taken by two ultra high-speed video cameras. We determined the ignition delay time was caught by analyzing the emission of light from the combustion chamber before knocking occurrence.

Distribution of injected fuel droplets, total hydrocarbon concentration and soot concentration in the combustion chamber of a diesel engine with a swirl chamber have been measured microscopically with regard to the time and the space by means of optical method. As a result of this study, effect of the swirl flow on atomized droplet distribution, relation between the droplets and hydrocarbon concentration, and relation between the change in concentration gradient of hydrocarbon with the time and the velocity of the swirl flow, and effect of non-luminous flame on the time of heat release rate raising period have been obtained. And from spatial distributions of hydrocarbon concentration, soot concentration, and local temperature in the combustion chamber at each time, the locational characteristics of soot generation are clarified. Further, effects of hydrocarbon and local temperature on soot generation have been considered.

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.

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.

The use of biodiesel fuels as an alternative fuel for petroleum diesel fuel is very effective for the reduction of CO2 emission, because biodiesel is produced from renewable biomass resources. Biodiesel is usually blended to conventional diesel fuel in various proportions. It is possible that this biodiesel blending causes the problems on emission characteristics of modern diesel engine, because it could be confirmed that the application of neat biodiesel to modern diesel engines whose control parameters were optimized for conventional diesel fuel deteriorated the emission performances. It is necessary to clarify the effect of biodiesel blending on exhaust emissions of modern diesel engine. Rapeseed oil methyl ester (RME) was selected as a biodiesel used in this study.