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Hydrogen can be readily used in spark-ignition engines as a clean alternative to fossil fuels. However, a larger burning velocity and a shorter quenching distance for hydrogen as compared with hydrocarbons bring a larger cooling loss from burning gas to the combustion-chamber wall. Because of the large cooling loss, the thermal efficiency of a hydrogen-fueled engine is sometimes lower than that of a conventionally fueled engine. Therefore, the reduction of the cooling loss is very important for improving the thermal efficiency in hydrogen-combustion engines. On the other hand, the direct-injection stratified charge can suppress knocking in spark-ignition engines at near stoichiometric overall mixture conditions. Because this is attributed to a leaner end gas, the stratification can lead to a lowered temperature of burning gas around the wall and a reduced cooling loss.

Recently, particulate matter (PM) emission from internal combustion engines, especially particles having the diameter of less than 100 nm (Nano-particles) are being considered for their potential hazards posed to human health and the environment. Nano-particles are unstable and easily influenced by the conditions of engine operation and measurement techniques. In this study, the influences of cooling and dilution processes on nano- particles are presented to understand the generation and dilution mechanisms, and to further development of an accurate measurement method. It is found that the thermo-dilurter is necessary for measuring the nano-particles with higher accuracy. Accurate measurement of nano-particles requires immediate dilution of the exhaust gases by hot air.

The results of this study make clear the characteristics of electrode performance deterioration in terms of cell voltage reduction in polymer electrolyte fuel cells (PEFCs) caused by the presence of certain quantities of carbon monoxide and/or hydrogen sulfide in the anode feed. AC impedance measurements of the anode and cathode potentials revealed that both electrode potentials showed deterioration in the presence of each type of poisoning gas. This suggests that the poisoning gases permeated the electrolyte membrane and transferred to the cathode, causing performance deterioration by poisoning the catalyst. In addition, AC impedance measurements indicated that the presence of hydrogen sulfide in the anode feed increased the membrane impedance, thus implying some poisoning effect even on the electrolyte membrane.

Reformed fuel from hydrocarbons or alcohol mainly consists of hydrogen, carbon monoxide and carbon dioxide. The composition of the reformed fuel can be varied to some extent with a combination of a thermal decomposition reaction and a water gas shift reaction. Methanol is known to decompose at a relatively low temperature. An application of the methanol reforming system to an internal combustion engine enables an exhaust heat recovery to increase the heating value of the reformed fuel. This research analyzed characteristics of combustion, exhaust emissions and cooling loss in an internal combustion engine fueled with several composition of model gases for methanol reformed fuels which consist of hydrogen, carbon monoxide and carbon dioxide. Experiments were made with both a bottom view type optical access single cylinder research engine and a constant volume combustion chamber.

Thermodynamic characteristics of premixed compression ignition combustions were clarified quantitatively by heat balance estimation. Heat balance was calculated from temperature, mole fractions of intake and exhaust gases, mass and properties of fuels. Heat balance estimation was conducted for three types of combustion; a conventional diesel combustion, a homogeneous charge compression ignition (HCCI) combustion; fuel is provided and mixed with air in an intake pipe in this case, and an extremely early injection type PREmixed lean DIesel Combustion (PREDIC). The results show that EGR should be applied for premixed compression ignition combustion to complete combustion at lower load conditions and to control ignition timing at higher load conditions. With an application of EGR, both HCCI and PREDIC showed low heat loss characteristics at lower load conditions up to 1/2 load.

The newly developed rotary engine has achieved major progress in high performance, improved fuel economy and clean exhaust gas by innovative action. The engine of the next generation is named RENESIS, which stands for “The RE (Rotary Engine)'s GENESIS” or the rotary engine for the new millennium. The peripheral exhaust port of the previous rotary engine is replaced by a side exhaust port system in the RENESIS. This allows for an increase in the intake port area, thus producing higher power. Exhaust opening timing is retarded to improve thermal efficiency. The side exhaust port also allows reducing the internal EGR, stabilizing the combustion at idling. The improved thermal efficiency and the stabilized idle combustion result in higher fuel economy. In addition, the side exhaust port allows a reduction of the HC mass, realizing reduced exhaust gas emission.

Homogeneous Charge Compression Ignition (HCCI) is effective for the simultaneous reduction of soot and NOx emissions from diesel engine. In general, high octane number and volatility fuels (gasoline components or gaseous fuels) are used for HCCI operation, because very lean mixture must be formed during ignition delay of the fuel. However, it is necessary to improve fuel injection systems, when these fuels are used in diesel engine. The purpose of the present study is the achievement of HCCI combustion in DI diesel engine without the large-scale improvements of engine components. Various high octane number fuels are mixed with diesel fuel as a base fuel, and the mixed fuels are directly applied to DI diesel engine. At first, the cylinder pressure and heat release rate of each mixed fuel are analyzed. The ignition delay of HCCI operation decreases with an increase in the operation load, although that of conventional diesel operation does not almost varied.

Particulate Matter (PM) from diesel engines is thought to be seriously hazardous for human health. Generally, it is said that the hazard depends on the total number and surface area of particles rather than total mass of PM. In the conventional gravimetric method, only the total mass of PM is measured. Therefore, it is very important to measure not only the mass of PM but also size and number density of particulates. Laser-Induced Incandescence (LII) is a useful diagnostic for transient measurement of soot particulate volume fraction and primary particle size. On the other hand, Scanning Mobility Particle Sizer (SMPS) is also used to measure the size distribution of soot aggregate particulates at a steady state condition. However, the measurement processes and the phenomena used to acquire the information on soot particulate are quite different between the LII and SMPS methods. Therefore, it is necessary to understand the detailed characteristics of both LII and SMPS.

This study analyzes the factors influencing the thermal efficiency of a homogeneous charge spark-injection (SI) engine fuelled with hydrogen, focusing on the degree of constant volume and cooling loss. The cooling loss from the burning gas to the cylinder walls is quantitatively evaluated by analyzing the cylinder pressure diagram and exhaust gas composition. The degree of constant volume burning and constant volume cooling are also obtained by fitting the Wiebe function to the rate of heat release calculated using the cylinder pressure diagram. A comparison of combustion and cooling characteristics of hydrogen and methane combustion reveals that cooling loss in hydrogen combustion is higher than that of methane combustion due to the short quenching distance and rapid burning velocity during hydrogen combustion. It is also suggested that the high cooling loss observed during hydrogen combustion reduces thermal efficiency.

The authors have developed a new partial flow dilution tunnel (hereafter referred to as PPFT), whose principal device is a flux splitting gas divider, as a new means of measuring particulate emissions which can be applied to transient cycle testing of diesel engines. The advantage of this system is that it can achieve perfect constant velocity splitting by means of its structure, and theoretically can also maintain high splitting performance despite fluctuations in the exhaust flow rate, including those due to engine exhaust pulsation. We compared this system with a full tunnel by analyzing the basic performance of the system and measuring particulate matter (PM) using an actual vehicle engine.

The full-flow dilution tunnel (hereinafter referred to as full tunnel) measurement method has become the de facto standard for the evaluation of particulate matter (hereinafter referred to as PM) emitted from diesel-powered vehicles. However, due to its drawbacks such as bulkiness and expensiveness, a method that uses a very small partial dilution tunnel (hereinafter referred to as micro tunnel) has been developed, mainly in Europe, nearly to the level of practicality. With this method, a higher degree of freedom in controlling sampling flow and temperature can be obtained. Another advantage of the micro tunnel is that the system is compact. However, the micro tunnel's measurement accuracy remains uncertain because the accumulation of measurement data is not yet sufficient. Measuring PM while varying micro tunnel operating parameters permitted a check on the equivalency with a full tunnel system.

A numerical study was carried out to investigate combustion characteristics of a dual-fuel gas diesel engine, using a multi-dimensional model combined with detailed chemical kinetics, including 43 chemical species and 173 elementary reactions. In calculations, the effects of initial temperature, EGR ratios on ignition, and combustion were examined. The results indicated EGR combined with intake preheating can favorably reduced NOx and THC emissions simultaneously. This can be explained by the fact that combustion mechanism is changed from flame propagation to HCCl like combustion.

Particulate matter (PM) and polynuclear aromatic hydrocarbons (PAH) were measured under steady state engine operating conditions in the exhaust of a DI diesel engine that meets the Japanese 1994 heavy-duty vehicle standards. In this study, to examine and discuss the effects of pyrene and sulfur contents in fuels on PM and PAH emissions, experiments were performed using both ordinary diesel fuel and a specified fuel having simple hydrocarbon components and very few aromatics. In the experiments, pyrene and sulfur contents in the fuels were changed by the addition of reagents to the fuel. The following conclusions were obtained. (1) From the experiments using ordinary JIS No. 2 diesel fuel with a pyrene reagent added to yield 400ppm pyrene, it was found that pyrene addition brings about an increase in soluble organic fraction (SOF) under low load engine operating conditions.

In this study, an experimental investigation was conducted using a direct injection single-cylinder diesel engine equipped with a test common rail fuel injection system to clarify how dimethyl ether (DME) injection characteristics affect the heat release and exhaust emissions. For that purpose the common rail fuel injection system (injection pressure: 15 MPa) and injection nozzle (0.55 × 5-holes, 0.70 × 3-holes, same total holes area) have been used for the test. First, to characterize the effect of DME physical properties on the macroscopic spray behavior: injection quantity, injection rate, penetration, cone angle, volume were measured using high-pressure injection chamber (pressure: 4MPa). In order to clarify effects of the injection process on HC, CO, and NOx emissions, as well as the rate of heat release were investigated by single-cylinder engine test. The effects of the injection rate and swirl ratio on exhaust emissions and heat release were also investigated.

Fuel composition is investigated as a parameter influencing fuel/air mixing of direct injected fuel and the subsequent consequences for particulate emissions. Presumably, enhanced mixing prior to ignition results in a larger portion of fuel burning as a premixture and a smaller portion of diffusion burning around fuel-rich regions. This would potentially lower particulate emissions without overly compromising hydrocarbon emissions or high load operation. Using mixtures of n-paraffin fuels, particulate emissions were measured and the results were compared with in-cylinder visualization of the injection process and two-color method calculations of flame temperature. In general, lower boiling point fuels exhibited higher flame temperatures, less visible flame, and lower particulate emissions.

The effect of boiling point difference as well as the flash boiling of two-component normal paraffin fuels on combustion and exhaust emission has been examined under different test conditions. To obtain a wide variation in boiling point between components different high boiling point fuels (n-undecane, n-tridecane and n-hexadecane) were blended with a low boiling point fuel (n-pentane) and different low boiling point fuels (n-pentane, n-hexane, and n-heptane) were blended with a high boiling point fuel (n-hexadecane). In addition the volume fraction of n-pentane was varied to have the best mixture ratio with n-tridecane. These fuel combinations exhibit different potential for flash boiling based on a certain ambient condition. The results indicate that though the potential for flash boiling is the highest for a mixture of n-pentane and n-hexadecane it emits about 20% higher PM than a mixture of n-pentane and n-tridecane.

Although various factors affecting oil consumption of an internal combustion engine can be considered, a technique to predict the amount of oil consumed within a cylinder that passes across a running surface of a ring was developed in this study. In order to predict the effect of cylinder deformation on oil consumption, a simple and easy technique to calculate the oil film thickness in deformed cylinder was proposed. For this technique, the piston ring was assumed to be a straight beam, and the beam bends with ring tension, gas pressure, and oil film pressure. From the calculated oil film thickness, amount of oil passing across the running surface of the TOP ring and into the combustion chamber was calculated. The calculated results were then compared to the oil film thickness of the ring and oil consumption measured during engine operation, and their validity was confirmed.

A diesel fuel and air diffusion flame burner system has been designed for laboratory simulation of diesel exhaust gas. The system consists of mass flow controllers and a fuel pump, and employs several unique design and construction features. It produces particulate emissions with size, number distribution, and morphology similar to diesel exhaust. At the same time, it generates NOx emissions and HC similar to diesel. The system has been applied to test plasma discharges. Different design discharge devices have been tested, with results indicating the importance of testing devices with soot and moisture. Both packed bed reactor and flat plate dielectric barrier discharge systems remove some soot from the gas, but the designs tested are susceptible to soot fouling and related electrical failures. The burner is simple and stable, and is suitable for development and aging of plasma and catalysts systems in the laboratory environment.

A study was performed on a lean NOx trap in which the loading of a ceria-containing mixed oxide in the washcoat was varied. After a mild stabilization of the traps, the time required to purge the NOx trap generally increased with increasing amount of mixed oxide. The purge NOx release also increased with increasing mixed oxide level but was greatly diminished after thermal aging. The sulfur tolerance of the NOx trap improved as the mixed oxide content was increased from 0% to 37%. The sample with 0% mixed oxide was more difficult to desulfate than the other samples due to poor water-gas-shift capability. After thermal aging, the NOx reduction efficiency on a 60 second lean/5 second rich cycle was highest for the samples with 0% to 37% mixed oxide at evaluation temperatures of 400°C to 500°C.

A dual fuel natural gas diesel engine suffers from remarkably lower thermal efficiency and higher THC, CO emissions at lower load because of its lower burned mass fraction caused by the lean pre-mixture. To overcome this inevitable disadvantage at lower load, two methods of reducing the number of operating cylinders were examined. One method was to use the two cylinders operation while the second one was to use the quasi-two cylinders operation. As a result, it was found that the unburned hydrocarbons and CO emissions could be favorably reduced with the improvement of thermal efficiency by reducing the number of cylinders to half for a dual fuel natural gas diesel engine. Moreover, it was also found that the quasi-two cylinders operation could improve the torque fluctuation more compared to the two cylinders operation.