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For diesel vehicles, NOx aftertreatment systems have become increasingly important, since the emission legislations continuously tightened. However, particulate matters (PM) and NOx aftertreatment systems have an impact on the engine operation and fuel penalties. Therefore, it is necessary either to find some auxiliary systems to decrease this impact or to find some brand new deNOx aftertreatment systems. In the literature, most research works concerning NOx and PM emission elimination using non-thermal plasma was conducted by employing either a dielectric barrier discharge (DBD) reactor alone or a plasma-assisted catalysis working under high temperature condition (over 150°C). Although there have been evidences that non-thermal plasma decomposes diesel PM but its mechanism is still not clear. In this paper, the simplified model for laboratory experiments consists of a wire-to-cylinder DBD reactor combined with a DPF was used to investigate NOx removal characteristics.

A six-stroke DI diesel engine proposed by the authors had second compression and combustion processes which were added on a conventional four-stroke diesel engine. This engine had the first and second power strokes before the exhaust stroke. Numerical predictions and experiments previously carried out had shown that this six-stroke diesel engine could reduce NO exhaust emission. Further, the ignition delay of the second combustion process could be shortened by a high temperature effect in the second compression stroke. This advantage of short ignition delay could be utilized for an ignition improvement of a fuel with low cetane number. In the engine system reported here, a conventional diesel fuel was supplied as the fuel of first combustion process, and in the second combustion process, methanol was supplied.

A high-speed photographic study is presented illustrating the influence of engine variables such as an introduced air swirl, the number of nozzle holes and the piston cavity diameter, on the combustion process in a small direct-injection (D.I.) diesel engine. The engine was modified for optical access from the under and lateral sides of the combustion chamber. This modification enabled a three-dimensional analysis of the flame motion in the engine. The swirling velocity of a flame in a combustion chamber was highest in the piston cavity, and outside the piston cavity it became lower at the piston top and at the cylinder head in that order. The swirl ratio of the flame inside the cavity radius attenuated gradually with piston descent and approached the swirl ratio outside the cavity radius, which remained approximately constant during the expansion stroke. Engine performance was improved by retarding the attenuation of the swirl motion inside the cavity radius.

In this paper, a new concept of an attitude control of a diesel spray was proposed. The Coanda effect known in the fields of the fluidics was applied to control a penetrating direction of a diesel spray injected into a combustion chamber of a D.I. diesel engine. In general, a jet moving along a wall was deviated by the Coanda effect. So if the shape of a cavity crown of the combustion chamber would be suitably designed and a diesel spray behavior would be similar to a gaseous jet, the spray might penetrate along the cavity wall. Furthermore, the switching effect of the penetrating direction might appear with a piston movement. To establish this method for an attitude control of a diesel spray, behavior of a diesel spray that was affected by a fixed interference plate located near the spray axis was experimentally investigated.

In order to clarify the trend of PM emission characteristic caused by fuel change, we propose a fundamental flame research method using a small pool flame system. Characteristics such as size distribution and formation rate of PM from laminar diffusion flames of gasoline fuels (JIS No.1 and No.2) were investigated by an electric microbalance and a SMPS (Scanning Mobility Particle Sizer). PM exhaust from flame of surrogate gasoline fuels and hydrocarbon fuels of various chemical structures were also measured. As the result, it was found that both of exhaust-PM concentration and PM number peak size increased with increasing of alkene and aromatic compositions in fuel.

Characteristics of PM and its compositions inside and outside of flame were required to develop reduction technologies for combustion origin PM. In this paper, relationship between PM size distribution and compositions such as soot and soluble organic fraction (SOF) of PM sampled with filter were investigated. Number distributions of PM (30 nm-10 μm) were measured using an ELPI (Electrical Low Pressure Impactor). Dry-soot and SOF in PM that was captured an individual stage of ELPI were analyzed using a combustion type PM analyzer (MEXA-1370PM). It was clarified that nuclei mode particle included more SOF than accumulation mode particle. PM characterization showed that there were many differences between in-flame PM and out-flame PM. In-flame PM contained much of low boiling point SOF and dry-soot composition was thermally unstable. Further, similarities between SOF in PM sampled with filter and gaseous hydrocarbons passing through PM filter were discussed.

Characteristics of fuel adhering after wall impingement of diesel spray were investigated experimentally. A flat wall, a recessed-wall which has a conical opening at impingement point, and a rugged-wall which has many concentric circular grooves, were used as an impingement wall. Diesel spray was impinged vertically to the wall in a high pressure chamber under a cold state. The spray behavior impinged on each of the three types walls was observed using a drum camera, which allowed high speed photographs. The spray after impingement on the recessed-wall was reflected from the wall with rolling-up motion, while the spray impinging on the flat wall was expanded along the wall surface to the radial direction. So, the recessed-wall might be expected to control the spray attitude in real engines. The spray height on the recessed-wall was higher than that on a flat wall. The amount of fuel stuck on each wall was measured by a precision balance.

Average concentration of a diesel impingement spray and characteristics of fuel adhering on a flat wall were investigated experimentally. Spray tip penetration and spray volume before and after impingement were measured on high speed photographs of the spray which was injected into a high pressure chamber of cold state. Further, the adhered fuel on the wall was directly measured by a precision balance. To clarify the characteristics of the impingement spray at various wall distances, pre-impingement spray and post-impingement spray were individually analyzed. Based on the entrainment air and fuel mass which was corrected by the adhered fuel, the air-fuel ratio was derived at various wall distances. As the results, the wall impingement of the diesel spray caused lean mixture spray concentration in comparison with the free spray. As the wall distance increased, the fuel film diameter to spray width ratio decreased.

Multi-stage injection diesel spray was investigated to understand the internal flow of a diesel spray. This multi-stage spray consisted of two sprays (we called them the first and second sprays) which were formed by a split injection with a short dwell time. In this paper, we discussed the dynamic behavior of a two-stage injection diesel spray. Especially, we focused on the characteristics of internal velocity and the decay of spray density fluctuation. When the injection rate of a conventional spray increased within an injection period, a spray tip of initially injected fuel was caught up and overtaken by the spray of a following injection. Then the internal structure of a conventional spray greatly depended on the internal spray velocity controlled by the injection rate. Since the second spray penetrated into the first spray, the spray tip motion of the second spray could be considered to be similar to the behavior of an internal spray motion in a conventional spray.

In this study, compositions, size distributions and activation energy in oxidation of diesel PM were investigated. Benzene (C6H6) was mixed to diesel fuel as a promoter of PM formation, and further, ferrocene (Fe(C5H5)2) was added as a promoter for oxidation processes during in-cylinder combustion and after-treatment. The effect of those additions on the PM characteristics was discussed on the basis of measured results such as SOF and dry-soot ratio in PM, primary and aggregate particle size distributions of PM, activation energy of PM oxidation, and PM components with elemental analysis. As a result, it was shown that ferrocene had special effect on the PM size distribution and the activation energy.

Effects of fumigated fuel on the initial combustion stage of a diesel spray were studied by measuring an ignition delay period and rate of heat release, clarifying a self-ignition limit of a fumigated fuel. Combustion experiments on both fumigated diesel fuel and methanol in a direct injection diesel engine gave the following results; a rapid combustion occurs with the methanol fumigation, while, the diesel fuel fumigation slightly changes the combustion of the main spray of diesel fuel injected directly into the combustion chamber. Regarding the rate of heat release, the maximum rate in the initial combustion stage increases rapidly with an increase in methanol fumigation, while for the fumigated diesel fuel, the maximum rate changes only slightly. The ignition delay period affected by fumigated diesel fuel is shorter than that affected by methanol at the same fumigation equivalence ratio and intake temperature.

New empirical equations to represent the Sauter mean diameter of a spray injected by a diesel nozzle are presented in this paper. In order to determine the new equations, drop sizes of a diesel spray were analyzed by a laser diffraction technique. Liquids with different viscosities and different surface tensions were tested to obtain the generalized empirical equations. The maximum injection and maximum ambient pressures were 90 MPa and 3.0 MPa respectively. Both the minimum value of the injection pressure to produce a fine spray and the Sauter mean diameter increase the greater the viscosity and the surface tension of the liquid. At a high injection velocity, the Sauter mean diameter increases with an increase in ambient pressure, but it decreases when ambient pressure is increased at a low injection velocity.

In this study, using a droplet dripping and evaporation test rig, over ten thousands droplets of diesel and bio-diesel fuels were dripped on a hot surface repeatedly, and evaporation deposits formed from them were quantitatively analyzed. Results show that wet-dry condition and hot surface temperature were main controlling factors of deposits development. Empirical equations of deposits development were derived from the experimental results. Further carbonaceous evaporation deposits from RME were around ten times serious than diesel fuel. The main reason of it was that bio-diesel fuel was produced from various plant oils through esterification and it was liquid phase chemical reaction process with no hot distillation, so that thermal stability of bio-diesel fuel was poor.

Recently, for reduction of PM emission from diesel engine, low sulfur diesel fuel was introduced and commercialized. There are some reports for effect of fuel sulfur on PM characteristics by using engine dynamometer tests. However, it is difficult to understand mechanism of PM formation and effect of fuel sulfur on PM formation process. Thus, investigation by a simple flame is effective way for understanding detail PM formation process. In this paper, effect of sulfur content in fuel on PM characteristics was investigated by using laboratory-scale PM generator. Test fuels were diesel and surrogate diesel fuel, and sulfur concentration in the surrogate fuel was controlled with thiophene addition. Effects of fuel sulfur on PM were clarified with characteristics of PM obtained from PM number distribution measurements and PM compositions analysis.

The purpose of this study was to investigate the effect of residual gas fraction and compositions on the ignition delay of a diesel spray. The air residual gas mixture was produced by injecting diesel sprays into a constant volume combustion bomb with no scavenging burned gas in it. The air initially contained in the bomb was enough to completely burn the fuel supplied by more than 20 injections. The spray injected in the bomb was ignited by the self-ignition process affected by the residual gas. Repetitions of the fuel injection raised the fraction of residual gas in the bomb. The ignition delay in each injection was measured by a photo-transistor. The ignition delay was a minimum when the ambient mixture contained about 4 % residual gas. The effect of residual gas compositions was investigated by adding small amount of CO, CO2 and THC into the bomb. The CO and CO2 compositions in the burned gas produced an elongation of the ignition delay, while the THC shortened the delay period.

The ignition and flame propagation processes of a propane-air mixture compounded with a kerosene spray were investigated in order to allow a better understanding of the multi-phase combustion process of the spray compound mixture in a direct injection stratified charge (DISC) engine. The ignition probability and the flame propagation velocity, as functions of the overall equivalence ratio, fraction of propane in the fuel, ignition energy and the Sauter mean diameter of the spray, were measured under atmospheric conditions. The development of the flame kernel and the propagating flame were observed by a high-speed video camera combined with a schlieren system. Adding small amounts of the kerosene spray to the lean propane-air mixture improved the ignition probability. However, the ignition probability depended strongly on the Sauter mean diameter and the ignition energy. Replacing the propane with the kerosene spray in a rich propane-air mixture increased the flame propagation velocity.

This paper presents the experimental analysis for the turbulence in the combustion chamber of a direct injection (D.I.) diesel engine. A dual beam mode, forward-scattering laser doppler velocimeter was applied to the flow measurement in a four-stroke, single-cylinder direct injection diesel engine of 110 mm bore and 125 mm stroke. The turbulence component was separated from instantaneous velocity using a high-pass filter. As a result, the difference in turbulent intensity between the intake and compression processes was discussed. Also, the effect of intake port and piston cavity shapes, the compression ratio and the engine speed on the turbulent intensity were clarified. In addition, the empirical equation for the decay of turbulent intensity in the compression process was expressed by a function of the Reynolds number based on the mean swirling flow.

The behavior of diesel spray impinging on an inclined wall was experimentally investigated in a pressurized vessel. To clarify the wall effect on a diesel spray, a relative angle of the inclined wall to a spray axis was varied. Spray penetration along the wall was observed optically and it was compared with that of a free spray. To evaluate various spray motion quantitatively, a spray path penetration which described a development of a spray tip along the wall was newly introduced. To observe an internal structure of the spray, it was visualized by a YAG laser sheet light and its tomographic image was captured on a film. The photo-image on a film was taken into an image analyzing computer using a high resolved image scanner. A high density zone in the tomographic image was extracted to clarify the internal structure of an impinging spray. The main parameter of the relative position of the wall was its inclined angle which was defined as the angle between the spray axis and wall.

The formation mechanism of Particulate Matter (PM) in a flame and fuel effect on this mechanism, are still under unclear problems. In this study, a fundamental pool combustion flame of diesel fuel was formed and PM emission from the flame was analyzed. As a result, though emission of soot from the flame was not observed, significant number of nuclei mode PM was emitted. From a flame of incomplete combustion, aggregate mode particles increased and nuclei mode particles reduced drastically. When a little mount of lubricant oil was contaminated into diesel fuel, number concentration of nuclei mode particle increased.

In this report, a new six-stroke diesel engine is proposed and the thermodynamic performances of this engine are numerically and experimentally analyzed. Since the six-stroke diesel engine introduced here has two combustion processes in one cycle, it offers new methods of combustion control which can't be attained in an ordinary four-stroke diesel engine. In the analysis, we use a simple single zone thermodynamic model with considering the Wiebe's function for heat release rate and the Woschni's equation for heat transfer coefficient. As a results, it was confirmed when the heat release of 1st combustion stroke and 2nd combustion stroke were equivalent, the maximum in-cylinder gas temperature was the lowest, and further it was lower than that of the four stroke diesel engine.