Search Results

Regarding S.I. gasoline engine, it is one of the most important matters to eliminate cyclic variation of combustion. Especially with high compression ratio and high boosted engine, the difficulties increase more. This paper describes the analysis of combustion process precisely by using many ion-current probes and CFD with the unique approaches. The number of used ion-current probes is 80 and they are mounted on whole combustion chamber wall especially including moving intake and exhaust valve faces. Thus cyclic variations of flame propagation can be measured precisely under high compression ratio and high boosted conditions in a multi-cylinder engine. In addition, CFD combustion simulation is conducted through full four strokes of continuous nine cycles. Moreover air motion and pressure vibration in intake and exhaust manifolds in whole cycles are considered. These unique approaches have made CFD result correspond to the measurement result of cyclic variations of actual combustion.

Attempts have been made to develop an electronically controlled fuel injection system that is ideal for small motorcycles, cost-efficient, compact, and electric power-saving while maintaining accuracy. For reducing the number of sensors and cost, highly accurate methods have been developed for the measurement of intake air mass, detection of acceleration, distinction of engine stroke, and estimation of atmospheric pressure without using a throttle position sensor, cam timing sensor, and barometric sensor in such a manner as to carry out sampling with the intake manifold pressure of single-cylinder engines synchronizing with the crank angle. For compactness and electric power saving, an injector and in-tank fuel pump module have been developed for small motorcycles.

Reduction in the cycle-to-cycle variation (CCV) of combustion in internal combustion engines is required to reduce fuel consumption, exhaust emissions, and improve drivability. CCV increases at low load operations and lean/dilute burn conditions. Specifically, the factors that cause CCV of combustion are the cyclic variations of in-cylinder flow, in-cylinder distributions of fuel concentration, temperature and residual gas, and ignition energy. However, it is difficult to measure and analyze these factors in a production engine. This study used an optically accessible single-cylinder engine in which combustion and optical measurements were performed for 45 consecutive cycles. CCVs of the combustion and in-cylinder phenomena were investigated for the same cycle. Using this optically accessible engine, the volume inside the combustion chamber, including the pent-roof region can be observed through a quartz cylinder.

Mixture formation is one of the most important factors for the combustion in the spark ignition engine with port fuel injection. The relation between combustion and mixture quality, however, is not quantitatively well established. In this study, the connection of combustion and mixture formation was explored with various measurement techniques. Borescopes were used in order to investigate the flame propagation in the combustion chamber and behavior of spray and fuel film on the wall in the intake port. For the purpose of investigation on the effect of mixture formation, various port fuel injection systems and parameters were tested and compared: direction, timing, and size of droplet. An SI engine for small vehicle was used under condition of 4 000 rpm. The investigation by images obtained has shown that inhomogeneity of mixture causes low combustion stability, especially due to direct introduction of fuel droplets into the combustion chamber.

A periodic impulsive sound at idle is occasionally described as ‘disagreeable’ in two-stroke engines. The relation between combustion conditions, piston vibrations, and the disagreeable sound is analyzed to clarify the phenomena. Some means to alleviate disagreeable sound are then proposed through stabilized combustion, high rigidity sound transfer systems, and refined skirt profiles. Experimental results are shown for the effects on main three factors evaluating disagreeable sound-loudness, impulsiveness, and frequency characteristics. In addition, piston behavior is measured, and the relation between piston motion and disagreeable sound is discussed in this paper.

In two-stroke engines, the exhaust port timing has a great effect on engine performance characteristics. If the exhaust port timing can be varied in response to variations in the engine speed, an extensive improvement of performance can be realized. The Yamaha Power Valve System (YPVS) increases engine output with a valve which operates in the exhaust passage; this valve controls exhaust port timing in response to engine speed, despite the extremely high thermal load encountered in the exhaust passage. This literature deals with the construction and operation principles of YPVS and its effect on the increase of engine output. Also discussed is a series of tests and measurements made on the delivery ratio and trapping efficiency in order to elucidate why engine output is increased.

This paper describes aspects of YAMAHA 2 cycle, high speed, high output engines. Generally speaking, in order to obtain good results in developing engine performance, high delivery ratios and high thermal and mechanical efficiencies are essential. In addition to these, the most suitable cooling and lubricating systems must be employed. YAMAHA has developed a separate and automatic lubrication system for 2-cycle gasoline engines, which keeps YAMAHA engines well lubricated.

In this study, an improvement of fuel consumption by changing the exhaust timing of a two-stroke engine has been made. The study results revealed that a remarkable improvement of fuel economy is possible by controlling the exhaust timing according to the engine speed. The reason for the better fuel economy was clarified through an analysis of exhaust gases, theoretical cycle calculations, and an analysis of combustion pressure. As an example of actual application, the results of tests made on an engine equipped with Yamaha power Valve System (YPVS), which is a variable exhaust timing mechanism using a tabor-shaped valve, will also be discussed.

THE MULTI-VALVE FOUR STROKE CYCLE engine design trend is Coward increased engine power and higher fuel efficiency. While a four-valve system is the most common direction, problems occur when the valve area is widened by increasing the cylinder bore for a higher engine output. The layout of four larger valves causes the combustion chamber shape to flatten and the combustion time period to increase. In pursuit of the optimum multi-valve engine we have studied four, five, six and seven-valve per cylinder design. Performance targets and design constraints led us toward the successful five-valve engine technology. This technology develops high engine torque and efficient combustion over a wide range of engine speeds.

The behavior of the liquid in the motorcycle fuel tank is an interesting theme from the viewpoint of the fuel meter construction, as effected by variance in the fuel pressure resulting from acceleration or deceleration, etc. It can be assumed that the behavior of the liquid in the fuel tank will be affected by the running pattern, the shape and capacity of the fuel tank, etc. Here is a report on an experiment recently made to observe how the liquid behaves in a partially fully enclosed tank. We simplified the tank shape and the involved conditions (to actually observe the behavior of the inside liquid by the suspension method.) Then we have analized the effectes according to different liquid containers, to different velocities, and to different liquid volumes as well as the time history variance in the internal pressure.

In order to obtain more reduction of two-stroke motorcycle engine noise than usual, it becomes necessary to make improvements within the combustion process itself. This study was carried out for two objectives. One is the investigation of the relationship between combustion and noise, and the other one is the development of noise reduction techniques. As the result, it was discovered that there was a significant correlation between engine noise and (dP/dθ)max, called the maximum rate of cylinder pressure rise. Therefore, the reduction of the (dP/dθ) max was recognized to be effective for engine noise reduction. The optimized alteration of combustion chamber shape is the most effective noise reduction technique, because it is able to reduce (dP/dθ) max without any sacrifice of engine power. In fact, the level of noise reduction can be predicted by one of the parameters obtained from the combustion chamber shape.

Measurement using a three-dimensional anemometric-tester was made for the gas flow inside the cylinder of a two-stroke engine while the shape of the transfer port was modified. The relationship between port shape and engine performance was investigated for various factors that characterize the flow in cylinder. In this paper, we focused mainly on two engine running conditions: the maximum output at 11750 rpm and the output at 10000 rpm. As a result, we found that the maximum output is most related to the tangential inclination angles of the main transfer port, and the inner vent radius of the main transfer duct.

An original multi-body dynamics simulation program for reciprocating engine system with elastically deformable piston skirt was developed in order to understand and examine the secondary motion of piston. This program uses specialized equations of motion using only the rotational degree of freedom of each components taking the valiation of rotating speed of crank into account. In order to validate the practical use of this program, the calculations were compared with the measurements on the piston motion of a two-stroke engine for motorcycles and a four-stroke engine for automobiles, and good agreements were obtained between them.

The demands on internal combustion engines for low emissions and fuel consumption are increasing year by year. On the other hand, engines to be used in motorcycles need to provide high output and quick response to meet user desire. In order to realize low fuel consumption while keeping high performance, it is necessary to properly understand cyclic variations during combustion as well as the influence of the injection system on fuel control during transient periods. The current paper reports on the results of a study in the influence of port fuel injection on combustion stability in a small displacement motorcycle engine, using both a series of experiments and CFD. The parameters of the injection systems under study are: (1) injection targeted area, (2) injection timing, and (3) fuel droplet size. The results of the current study show that injection aimed at the upstream wall yielded the best combustion stability.

A construction of the technology concerning fuel consumption improvement is an important problem not only for the four-wheeled vehicle but also for the motorcycle in recent years when petroleum resources are depleted rapidly. Yamaha originally developed a new fuel injection system (YMJET-FI) and applied the system to a single cylinder, water-cooled and small-displacement engine. In this paper, we would introduce the results of improving the fuel economy with keeping high performance. Improvements were noted in three matters, namely, in the lower load range, 1.Strengthening of in-cylinder flow, 2.Atomization of fuel spray, and 3.Reduction of wall film quantity.

This paper reports visualization of behavior of spray, wall film, and initial flame propagation in an SI engine with port fuel injection system for motorcycle in order to directly investigate their influences on combustion and relations among them. Borescopes were used to visualize the flame propagation in the combustion chamber and wall film in the intake port. Various injection systems and injection parameters were tested: injection direction, timing, and size of droplets to investigate the effect of mixture formation. It is concluded that combustion stability under low load condition is greatly influenced by mixture inhomogeneity in the combustion chamber whose evidence is the luminous emission. It is caused by direct induction of considerable amount of liquid fuel with large size of droplets into combustion chamber or too inhomogeneous mixture in the intake port.

The two-stroke engines were in the main stream of the outboard motors, but they have been replaced with the four-stroke counterparts reflecting the environmental protection movement in recent years. However, the replacement with four-stroke engines involves increased number of components and additional displacement, and the outboard motors tend to be larger and heavier. This represents an issue, since the maneuverability of the boat is degraded due to the inappropriate weight distribution on the boat. Yamaha outboard motors F300B and VF250A, of which the production started in the year 2009, are equipped with four-stroke engines, and yet achieved the light weight equivalent to their two-stroke counterparts. The production volume of these models reached 20,000 units.