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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.

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.

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.

Taking note of the value of the maximum delivery ratio Km produced by the inertia effect, the authors qualitatively considered the influences of the atmospheric conditions and the engine factors to compare them with the experimental. It is ascertained that the value od maximum delivery ratio depends on the inertia effect and the theoretical results correspond fairly well with those of the experimental value.

In a gasoline engine, it is most important to recognize the behavior of fuel liquid-film flow in the intake pipe. Accordingly, the authors have tried to measure directly the amount of fuel liquid-film flow by means of the each separator inserted in the intake manifold and at the same tine to record the instantaneous behavior of liquid-film thickness from the change in electric conductivity. Especially, the experimental results on the measuring method of fuel liquid-film thickness will be described in this paper.

In a two-stroke cycle engine, it is impossible to except the effect of engine brake, owing to its structure. However, since the necessity of engine brake has increased with increasing the vehicle speed, and with increasing the complexity of traffic problems, it is demanded to solved. For this reason, the authors investigated the mean frictional loss pressure of engine, and the effect of releasers on the engine brake with a crankcase-compression two-stroke cycle engine. The results, one of the weak points on a two-stroke cycle engine be solved completely by the application of releaser.

It is important not only to increase a thermal efficiency of a spark ignition engine, but also to decrease a driving loss of auxiliary component of engine such as a cooling system. For example, there is a limitation of cooling performance when a requirement of aerodynamics design of a motorcycle or an automobile is severe. We propose an active application of ejector pump drove by exhaust energy to the cooling system. There were several applications of ejector system to the intake or exhaust system, but there was nothing for the design of it. In this report, one of the fundamental researches conducted in our laboratory, the effects of the dimensions of the ejector on the ejector performance are discussed. The results are followings: (1) The more the engine speed decreases, the more the ejector efficiency (G2/G1: G1 is the mass of charging air in the engine, G2 is the mass of entrained air by the ejector system) increases.