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A two-stroke engine has various advantages. It is simple in structure, light in weight, high in mechanical efficiency, superior in accelerating ability, etc. However, its fuel consumption is bad, its combustibility under partial load is poor and it is usually accepted that its exhaust gas is problematic. With increasing traffic flow volume, it has become recently necessary to operate transiently each vehicle with frequent stops and starts, as well as decelerations and accelerations. From this standpoint, the authors have formed a simple dynamic model of two-stroke engine, and by means of simulation investigated how its performance can be improved while it is transiently operated, in combination with experiment. The results confirm that the calculations from the model coincide approximately with experiment. The influences of various factors on the performance have been revealed.

In this study, accordingly, methanol fuel was supplied in suction pipe with carburetor and with electronically-controlled fuel injector (EFI), which located in front of the suction valve, to clear experimentally the influence of various factors, such as the methanol-gasoline ratio (M/F), the difference in fuel feed system, the number of times of injection [ni], the injection timing (θinj), the engine speed (N), the volumetric efficiency (η v), the suction pipe wall temperature (tw), the water content in fuel (yw) etc., on the engine performance (the output and the thermal efficiency), the exhaust characteristics (NOx, CO, UBF and HCHO concentrations) and combustion variation as well as obtaining a guideline to establish the optimum condition. The authors will be report about the results of above-mentioned.

Under the accelerating or decelerating operation, it is demanded to improve the performance and reduce the exhaust smoke of diesel engines. Regarding the exhaust smoke regulation for a vehicle engine under transitional operation, the so-called free or controlled accelerating operation, are adopted as the simple measuring method. And the engine applied for the construction or agriculture is always operating under the load conditions of stepwise or periodical changes. For two-stroke engines, in particular, the effects of operating conditions on the engine performance and the smoke character are unclear. In order to meet such demand, it is necessary to make clear the transitional character of each transfer element, i.e., the fuel injection system, the combustion process and the frictional loss.

Reduction of soot and NOx emissions from a prechamber-type diesel engine is studied by employing both chemical and physical aspects of the fuel and induction method. Fuel modification was performed to produce several forms of composite fuel: solution of alcohol and gas oil (JIS No. 1); emulsification and mixture of methyl alcohol-gas oil prepared by off- and in-line fuel systems; and separate injection of fuels into the pre- and main-chamber.

To examine the effects of exhaust gas recirculation (EGR) on the exhaust emissions and on the cycle-by-cycle variation of combustion process in a methanol engine, the authors have tried to measure the emissions of total hydrocarbon, carbon monoxides, nitric oxides and formaldehyde and to record the cylinder pressure development histories of 1000 cycles duration. Moreover, the standard deviation of peak pressure Pmax, the heat release rate and the averaged pressure history are analyzed. The results are compared with those of gasoline fueled operation.

The engine performance, combustion characteristics and exhaust emission of pre-chamber type compression ignition engine operated by various biomass fuels were investigated experimentally. The biomass fuel investigated in this report are an emulsified fuel made with gas oil and hydrous ethanol or hydrous methanol, an emulsified fuel made with hydrous methanol and rape-seed oil, and neat rape-seed oil, and gas oil. There are small deviations of the experimental results between the biomass fuels, however, the general tendencies of the engine performances and exhaust gas characteristics operated by biomass fuels are as follows: The brake thermal efficiency during biomass fuel operation becomes maximum at a certain injection timing as well as those of the gas oil operation. And this injection timing is advanced with increasing the biomass content in the fuel.

So far the studies on the dynamic characteristic of internal combustion engines have been mainly carried out on the governor system and have led to development of a mathematical model more efficient for simulation and control purpose. But, there are still uncertain dynamic behaviors of the engine. The experiment and analysis on the transfer characteristic of effective torque and engine speed under a changing fuel feed quantity or brake load were carried out by using the frequency response and step response methods. Consequently, it was confirmed that the transfer response of effective torque and engine speed to the changes in fuel feed quantity or brake load comprises a response time lag and its time constant is variable with the operating condition of the engine.

If the water/gas-oil-emulsion fuel is to be used in a compression ignition engine, it is necessary not only to carry out directly engine experiment but also to determine the characteristics of so-called mixture formation process, including those of fluidity, spray mode, injection rate and evaporation in high-temperature environment and on high-temperature wall as well as the influence of these characteristics on engine performance. In this report, the authors have experimentally investigated on the physical properties and injection characteristics of water/gas oil-emulsion fuel (W/O).

Dimethyl Ether (DME) is a promising new alternative fuel for compression ignition DI engines. However, some problems arise from the poor lubricity of DME. Breakdown of the film bearing between needle and sleeve of the injector can lead to mechanical wear and leakage, a problem that is not mitigated easily. For example, the application of returning the leakage to fuel tank could raise a back pressure on the injection needle. This pressure can affect injection rate and consequently engine performance. In this study, fuels based on various DME to gas oil (diesel fuel) ratios were investigated, in part. Physical and chemical properties of DME and gas oil are shown to lead to mutual solubility at any ratio. Blended fuels have a higher lubricity compared with pure’ DME and a better injection spray compared with pure gas oil.

Hydrogen produced from regenerative sources has the potential to be a sustainable substitute for fossil fuels. A hydrogen internal combustion engine has good combustion characteristics, such as higher flame propagation velocity, shorter quenching distance, and higher thermal conductivity compared with hydrocarbon fuel. However, storing hydrogen is problematic since the energy density is low. Hydrogen can be chemically stored as a hydrocarbon fuel. In particular, an organic hydride can easily generate hydrogen through use of a catalyst. Additionally, it has an advantage in hydrogen transportation due to its liquid form at room temperature and pressure. We examined the application of an organic hydride in a spark ignition (SI) engine. We used methylcyclohexane (MCH) as an organic hydride from which hydrogen and toluene (TOL) can be reformed. First, the theoretical thermal efficiency was examined when hydrogen and TOL were supplied to an SI engine.

Dimethyl ether (DME) holds promise as an alternative to diesel fuel. However, its physical properties are not similar to those of conventional diesel fuel. The P-V, bulk modulus and viscosity of DME are derived as a function of temperature and pressure. As a result, the Weber and Reynolds number of DME is very large as compared with that of diesel fuel. So, the spray characteristics of DME are not those of a liquid spray but similar to those of gas spray. The spray formation is strongly affected by the fuel flow in the nozzle. The Computational Fluid Dynamics (CFD) and experiments are examined to analyze the fuel flow in the nozzle. The DME physical properties make some difference to the flow in the nozzle, in comparison with those of diesel. As a CFD result, cavitation in the injection nozzle is more frequent with DME than with diesel oil. From experimental results, the temperature in the nozzle sac is higher with DME than with diesel oil.

Recently, dimethyl ether (DME) has been attracting much attention as a clean alternative fuel, since the thermal efficiency of DME powered diesel engine is comparable to diesel fuel operation and soot free combustion can be achieved. In this experiment, the effect of ambient pressure on DME spray was investigated with observation of droplet size such as Sauter mean diameter (SMD) by the shadowgraph and image processing method. The higher ambient pressure obstructs the growth of DME spray, therefore faster breakup was occurred, and liquid column was thicker with increasing the ambient pressure. Then engine performances and exhaust emissions characteristics of DME diesel engine were investigated with various compression ratios. The minimum compression ratio for the easy start and stable operation was obtained at compression ratio of about 12.

Dimethyl Ether (DME) is one of the major candidates for the next generation fuel for compression ignition (CI) engines. It has good self-ignitability and would not produce particulate, even at rich conditions. DME has proved to be able to apply to ordinary diesel engines with minimal modifications, but its combustion characteristics are not completely understood. In this study, the behavior of a DME spray and combustion process of a direct injection CI engine fueled with DME was investigated by combustion observation and in-cylinder gas sampling. To distinguish evaporated and non-evaporated zones of a spray, direct and schlieren imaging were carried out. The sampled gas from a DME spray was analyzed by gas chromatography, and the major intermediate product histories during ignition period were analyzed.

Dimethyl ether(DME) is a promising new alternative fuel not only diesel fuel but also power generation, fuel cell and city gas. However, the physical properties are not similar to those of conventional diesel fuel. The P-v, bulk modulus and viscosity of DME are derived as a function of temperature and pressure. As a Result, the Weber and Reynolds number of DME is very large as compared with that of diesel fuel. So, the spray characteristics of DME is not the liquid spray but similar to that of gas spray. The spray formation is strongly affected by the fuel flow in the nozzle. The Computational Fluid Dynamics (CFD) and the experiments are examined to analyze the fuel flow in the nozzle. The DME physical properties make some difference of the flow in the nozzle, comparing with those of diesel. As a CFD result, cavitation in the injection nozzle is more frequent with DME than with diesel oil.

Characteristics of dimethyl ether spray formation were observed using schlieren photography, and the combustion characteristics and performance of a dimethyl ether-operated diesel engine were investigated. Accordingly, this paper describes the basic characteristics of engine performance and the potential for decreased exhaust emissions, as well as discussing problems concerning the practical application of dimethyl ether-operated diesel engines.

Many studies on the Cyclic variation of combustion process are made with a spark ignition engine. However, there are scarcely such studies with a diesel engine. Because, in general, the combustion of diesel engine is believed very stable. However, there exist some combustion variations in a diesel engine. As it is universally known, the combustion in a diesel engineis the series of a pre-mixed and a diffusion combustion, which is completely different from the combustion of a spark ignition engine. Therefore, it is impossible to determine the combustion variation of diesel engine by a direct application of the results of spark ignition engine. In this report, we discuss the several factors which indicate the combustion variation with a pre-chamber type diesel engine. The maximum pressure Pmax, the maximum rate of pressure rise (dP/dθ )max, the combustion pressure at each crank angle, etc. are analyzed from the continuous five handred of combustion pressure histories statistically.

A water/Oil type emulsified fuel has been demonstrated to decrease the harmful exhaust emissions and increase a thermal efficiency of internal combustion engine experimentally(1)*. However, an emulsified fuel is not currently used for internal combustion engines. When we try to use an emulsified fuel for the internal combustion engines, especially for a compression ignition engine, we should clear the physical properties of emulsified fuel. Because the viscosity of the emulsified fuel affects the spray characteristics and following combustion characteristics. It is commonly recognized that the viscosity of emulsified fuel is much higher than that of the base fuels. However, there are no data which show the viscosity increase of emulsified fuel. We proposed an newly introduced specific surface area Sp/Se to estimate the viscosity of the emulsified fuel.

Under accelerating or decelerating operation, it is demanded to improve the performance and to reduce the exhaust smoke of diesel engines. Regarding the exhaust smoke regulation for a vehicle engine under transitional operation, the so-called free or controlled accelerating operation, are adopted as the simple measuring method. And the engine applied the construction or agricultural use is always operating under the load conditions of stepwise or periodical changes. For two-stroke cycle engines, in particular, the effects of operating conditions on the engine performance and the smoke character are unclear. In order to meet such demand, it is necessary to make clear the transitional character of each transfer element, i.e., the fuel injection system, the combustion process and the frictional loss.

A direct fuel-injection two-stroke cycle engine operated with neat methanol was investigated. The engine performance, combustion and exhaust-gas characteristics were analyzed experimentally and compared for operation with a carburetor, EFI injection at the intake manifold, and EFI injection at the scavenging port. The power and the brake thermal efficiency of the direct fuel-injection engine were higher than those of engines operated with a carburetor and either of the two EFI methods. The exhausted unburnt fuel of the direct fuel-injection engine was lower than that for operation with a carburetor, and formaldehyde and the CO concentration were of the same level as for operation with the carburetor and EFI methods. The NOx concentration of the direct fuel-injection was half the level of the result of carburetor operation.

Effects of the intake air oxygen enrichment (IOE) on the combustion processes and performance of a spark ignition (SI) engine were investigated when the engine was operated under part load conditions both after and during the warm-up period. The study was performed by comparing the direct measurements of engine performance and emission characteristics with instantaneous digital imaging of in-cylinder reaction processes obtained using our high-speed dual-spectra infrared imaging system developed at Rutgers. The IOE under the partial load operations of an SI engine produced some comparable improvements in the thermal efficiency and mean effective pressure to those from the full load operations. Although no dramatic reduction of unburned hydrocarbon emissions with the IOE was realized in the present measurement, the insignificant increase of Nox under the same condition is noteworthy.