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A free piston engine linear generator (FPEG) with potential for compact build, high efficiency and high fuel flexibility was developed in this study. The FPEG consists of a two-stroke combustion system, a linear generator, and a gas spring chamber. There are some technical challenges in ensuring an FPEG can achieve continuous operation over a long period, including lubrication, cooling, and piston motion control. Among these technical challenges, the piston motion control is the most significant factor in improving the robustness and efficiency of the FPEG because the combustion characteristics depend strongly on the piston motion, which is controlled by the linear generator. This paper describes a novel linear generator control method which realizes the simple harmonic oscillation governed by the piston mass and the air spring pressure. In general, the generating efficiency of linear generators is low in the low-speed region.

Free Piston Engine linear Generator (FPEG) that is thin and compact and has high efficiency and high fuel flexibility has been developed. The developed FPEG consists of a two-stroke combustion chamber, a linear generator, and a gas spring chamber. This paper focuses on the control logic of the linear generator, where the generator can be changed instantly to act as a driving motor, according to demand. Both the position and velocity of the piston are selected as feedback parameters for the control logic. The proposed feedback method realizes stable and robust control behavior with respect to abnormal combustion conditions, such as pre-ignition. In addition, the control logic must satisfy the following requirements. First, in order to achieve stable two-stroke combustion, the position of the piston is precisely controlled, especially near the top dead center (TDC) and the bottom dead center (BDC).

Free Piston Engine Linear Generator (FPEG) with features of thin and compact build, high efficiency and high fuel flexibility is developed. The FPEG consists of a two-stroke combustion chamber, a linear generator and a gas spring chamber. The key technologies to realize stable continuous operation are lubricating, cooling, and control logic. This paper proposes the original structure of the FPEG for enabling stable continuous operation. The main feature is a hollow circular step-shaped piston. The smaller-diameter side of the piston constitutes the combustion chamber, and the larger-diameter side constitutes the gas spring chamber. The larger cross-sectional area of the gas spring chamber leads to lower compression temperature of the gas spring chamber and consequently decreased heat loss. In addition, an oil cooling passage is built in the column stay, which ensures the enough cooling ability of the piston.

The aim of this work is to investigate the possibility of heat insulation by “Temperature Swing”, that is temperature fluctuation, on combustion chamber walls coated with low-heat-conductivity and low-heat-capacity materials. Adiabatic engines studied in the 1980s, such as ceramic coated engines, caused constantly high temperature on combustion wall surface during the whole cycle including the intake stroke, even if it employed ceramic thermal barrier coating methods. This resulted in increase in NOx and Soot, decrease in volumetric efficiency and combustion efficiency, and facilitated the occurrence of engine knock. On the other hand, “Temperature Swing” coat on the combustion chamber walls leads to a large change in surface temperature. In this case, the surface temperature with this insulation coat follows the transient gas temperature, which decreases heat loss with the prevention of intake air heating, and also which is expected to prevent NOx and Soot from increasing.

The effects of an increasing boost pressure, a high EGR rate and a high injection pressure on exhaust emissions from an HSDI (High Speed Direct Injection) diesel engine were examined. The mechanisms were then investigated with both in-cylinder observations and 3DCFD coupled with ϕT-map analysis. Under a high-load condition, increasing the charging efficiency combined with a high injection pressure and a high EGR rate is an effective way to reduce NOx and soot simultaneously, which realized an ultra low NOx of 16ppm at 1.7MPa of IMEP (Indicated Mean Effective Pressure). The flame temperature with low NOx and low soot emissions is decreased by 260K from that with conventional emissions. Also, the distribution of the fuel-air mixture plot on a ϕT-map is moved away from the NOx and soot formation peninsula, compared to the conventional emissions case.

We have developed a novel engine cycle simulation program (UniDES: universal diesel engine simulator) to reproduce the diesel combustion process over a wide range of engine operating parameters, such as the amount of injected fuel, the injection timing, and the EGR ratio. The approach described in this paper employs a zoning model, where the in-cylinder region is divided into up to five zones. We also applied a probability density function (PDF) concept to each zone to consider the effect of spatial non-homogeneities, such as local equivalence ratios and temperature, on the combustion characteristics. We linked this program to the commonly used commercial GT-Power® software (UniDES+GT). As a result, we were able to reproduce transient engine behavior very accurately.

A concept of dual-fuel, Premixed Compression Ignition (PCI) combustion controlled by two fuels with different ignitability has been developed to achieve drastically low NOx and smoke emissions. In this system, isooctane, which was used to represent high-octane gasoline, was supplied from an intake port and diesel fuel was injected directly into an engine cylinder at early timing as ignition trigger. It was found that the ignition timing of this PCI combustion can be controlled by changing the ratio of amounts of injected two fuels and combustion proceeds very mildly by making spatial stratifications of ignitability in the cylinder even without EGR, as preventing the whole mixture from igniting simultaneously. The operable range of load, where NOx and smoke were less than 10ppm and 0.1 FSN, respectively, was extended up to 1.2MPa of IMEP using an intake air boosting system together with dual fueling.

The effects of multiple-injection on exhaust emissions and performance in a small HSDI (High Speed Direct Injection) Diesel engine were examined. The causes for the improvement were investigated using both in-cylinder observation and three-dimensional numerical analysis methods. It is possible to increase the maximum torque, which is limited by the exhaust smoke number, while decreasing the combustion noise under low speed and full load conditions by advancing the timing of the pilot injection. Dividing this early-timed pilot injection into two with a small fuel amount is effective for further decreasing the noise while suppressing the increase in HC emission and fuel consumption. This is realized by the reduced amount of adhered fuel to the cylinder wall. At light loads, the amount of pilot injection fuel must be reduced, and the injection must be timed just prior to the main injection in order to suppress a possible increase in smoke and HC.

Through the basic research of the plasma assisted catalyst system using DeNOx catalysts and the gas analysis of the system, its conceptual use for automobile diesel engine applications has been studied. This study has shown that the length between the plasma reactor and the catalyst reactor does not affect the NOx conversion. To obtain an efficient NOx conversion, the plasma should affect both the HC as the reductant and NOx at the same time. In the case of γ-Al2O3 and C3H6, the main component for NOx reduction was CH3CHO generated by the plasma. Under 250 deg. C, the temperature was too low for the γ-Al2O3 to become effective. Therefore, the NOx conversion became low. At 400 deg. C, the NOx conversion became high. However, at 600 deg. C, the CH3CHO for reducing NOx was not generated, and the NOx conversion decreased.

NOx reduction activity in an oxidizing exhaust gas was significantly improved by discharging non-thermal plasma and catalysts (plasma assisted catalysis). We investigated effective catalyst for plasma assisted catalysis in view of hydrocarbon-selective catalytic reduction(HC-SCR). Plasma assist was effective for γ-alumina and alkali or alkaline earth metals loaded zeolite and γ-alumina showed the highest NOx conversion among these catalysts. On the other hand, Plasma assist was not effective for Cu-ZSM-5 and Pt loaded catalyst. The NOx conversion for the plasma assisted γ-alumina decreased by formation of a deposit on the catalyst below 400°C. It is shown that indium loading on γ-alumina improved the NOx reduction activity and suppressed the degradation of the NOx reduction activity at 300°C with plasma assist.

A new technique using Laser-Induced Incandescence (LII) has been developed to quantify the soot concentration in a diesel engine. Characteristic problems in quantitative measurements, such as LII signal attenuation by soot clouds between the camera and the measurement plane, and incident laser attenuation due to soot clouds in the laser path, were corrected by the multi-layer correction method developed in this work. When this LII measurement method is applied to an optically accessible engine, the developing soot clouds in spray combustion can be visualized in detail. The changes in soot formation process caused by increasing fuel injection pressure with reduced hole size of injector, and by altering fuel chemical property, are both clarified quantitatively in this paper.

Exhaust emissions and combustion characteristics from well-characterized diesel test fuels have been measured using two types of single-cylinder HSDI diesel engines. Data were collected at several fixed speed/load conditions representative of typical light-duty operating conditions and full-load performance (smoke-limited maximum torque) points. In addition, in-cylinder soot formation processes of these fuels were investigated via Laser Induced Incandescence (LII) using an optically accessible single-cylinder engine. The test fuels used in this study have been formulated with a sophisticated blending algorithm that systematically varies the hydrocarbon molecular structure in the fuels while maintaining the distillation characteristics of market diesel fuels. The following results have been obtained from this study. (1) The lowest PM emissions were observed with a fuel containing approximately 55% iso-paraffins and 39% n-paraffins with CN=52.5.

The cause of the exhaust smoke and its reduction methods in a small DI Diesel engine with a small-orifice-diameter nozzle and common rail F.I.E. were investigated under high-speed and high-load condition, using both in-cylinder observations and Three-dimensional numerical analyses. The following points were clarified during this study. At these conditions, fuel sprays are easily pushed away by a strong swirl, and immediately flow out to the squish area by a strong reverse squish. Therefore, the air in the cavity is not effectively used. Suppressing the airflow in a piston cavity, using such ideas as enlarging the piston cavity diameter or reducing the port swirl ratio, decreases the excessive outflow of the fuel-air mixture into the squish area, and allows the full use of air in the whole cavity. Hence, exhaust smoke is reduced.

Some methods to quantify the soot concentration by Laser-Induced Incandescence were developed using a flat flame burner in our previous work [1]. Those methods take the following points into consideration. (1)a correction of the LII signal intensity profile distorted by the laser attenuation due to soot clouds on the laser path, (2)a correction of the LII signal intensity attenuated by soot clouds between a camera and a measurement plane, (3)soot particle sizing up using 2-color LII signals and (4)conversion from a signal intensity to a soot concentration based on a calibration data. Using the methods, the accuracy of less than 10% was achieved in soot concentration measurement by a flat flame burner. In this study, the above methods were applied to an optically accessible single-cylinder diesel engine to measure in-cylinder soot concentration quantitatively.

The effect of the chemical reactivity of diesel fuel on PM formation was investigated using a flow reactor and a shock tube. Reaction products from the flow-reactor pyrolysis of the three diesel fuels used for the engine tests in Part 1(1) (“Base”, “Improved” and Swedish “Class-1”) were analyzed by gas chromatography. At 850C, Swedish “Class-1” fuel was found to produce the most PM precursors such as benzene and toluene among the three fuels, even though it contains very low amounts of aromatics. The chemical analyses described in Part 1 revealed that “Class-1” contains a large amount of branched and cyclic structures in the saturated hydrocarbon portion of the fuel. These results suggest that the presence of such branched and ring structures can increase exhaust PM emissions.

Combustion and exhaust emission characteristics were compared among three representative diesel fuels called “Base (corresponding to a Japanese market fuel)”, “Improved” and Swedish “Class-1” using both a modern small and an optically accessible single-cylinder DI diesel engines. In these tests, the relative amount of PM collected in the exhaust was “Base” >“Class-1” >“Improved” at almost all of the operating conditions. This means that “Class-1” generated more PM than “Improved”, even though “Class-1” has significantly lower distillation temperatures, aromatic content, sulfur, and density compared with “Improved”. There was little difference in combustion characteristics such as heat release rate pattern, mixture formation and flame development processes between these two fuels. However, it was found that “Class-1” contained more branches in the paraffin fraction and more naphthenes.

Means for reducing the particulate matter (PM) from swirl chamber type diesel engines were searched out, and the reducing mechanisms were examined using an optically accessible engine. The following points were clarified in this study. 1. At light load, the suppression of the initial injection rate reduces PM, because SOF is reduced by the change in ignition point and smoke is reduced by the retarded flowout of the dense soot from the swirl chamber 2. Under medium and high load conditions, the main cause of the exhaust smoke is fierce spray-wall impingement which leads to fuel adhesion on the wall and the stagnation of a rich fuel-air mixture. 3. Enlarging swirl chamber volume ratio suppresses the formation of dense soot in the swirl chamber. In the main chamber, however, the soot oxidization becomes insufficient due to the mixing effect reduced by the essentially decreased chamber depth. 4.

The compositions of hydrocarbons in diesel fuel, exhaust gas and particulates were analyzed and the relationships among them were determined. It was found that the compositions of the hydrocarbons in the exhaust gas were almost the same as that of the fuel, and that the hydrocarbons in the particulates corresponded to their heavy fractions. When the engine condition was fixed, both the soluble organic fraction (SOF) and insoluble fraction ( ISF) showed positive correlation coefficients versus HC×R310, where HC denotes the hydrocarbon emission and R310 denotes the backend fraction, as measured by the fraction of fuel boiling above 310°C. On the other hand, when the engine condition was varied, ISF had negative correlation coefficients versus HC×R310, while SOF showed positive correlation coefficients.

Soot formation process was examined by high speed photographs, using a single cumbustion diesel engine with a transparent swirl chamber. Fuel-air mixture and flames, and soot clouds were visualized by the schlieren method and the back-illuminated method, respectively. A three dimensional simulation program with soot formation and oxidation models was developed to clarify diesel soot formation processes. The models consist of several models previously proposed and partly improved in this study. Good agreement was obtained between calculated and experimental results. The following points were clarified through observation and numerical studies: (1) The main soot area is considerably smaller than luminous flame area, especially in the initial soot formation process. (2) The main soot cloud first appears in the tip region of fuel-air mixture, downstream of ignition position a few submilliseconds after the ignition.