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This study deals with reduced-order modeling of intake air dynamics in single-cylinder four-stroke naturally-aspirated spark-ignited engines without surge tanks. It provides an approximate calculation method for embedded micro computers to estimate intake manifold pressures in real time. The calculation method is also applicable to multi-cylinder engines with individual throttle bodies since the engines can be equated with parallelization of the single-cylinder engines. In this paper, we illustrate the intake air dynamics, describe a method to estimate the intake manifold pressures, and show experimental results of the method.

In four-cycle single-cylinder motorcycle engines, high Hertzian stress is generated on and beneath the big-end surface of the connecting rod. If the surface strength would be improved, the diameter of the big-end could be made smaller, making the entire engine smaller and lighter. Therefore, application of carbide dispersion carbonitriding using a vacuum furnace (hereinafter referred to as “vacuum CD carbonitriding”) on the big-end surface was investigated. Vacuum CD carbonitriding was carried out by three processes. The first was a CD carburizing process. This process is done to obtain granular cementite, but in order to avoid decreasing the strength, it is necessary to prevent the formation of coarsened cementite at the grain boundary. The second process was a refining process. This process is done for the purpose of refining the prior austenite grain size. The third process was a carbonitriding process.

Gasoline fueled Homogeneous Charge Compression Ignition (HCCI) combustion with internal exhaust gas re-circulation using Negative Valve Overlap (NOL) was investigated by means of calculation and experiment in order to apply this technology to practical use with sufficient operating range and with acceptable emission and fuel consumption. In this paper we discuss the basic characteristics of NOL-HCCI with emphasis on the influence of intake valve timing on load range, residual gas fraction and induction air flow rate. Emission and fuel consumption under various operation conditions are also discussed. A water-cooled 250cc single cylinder engine with a direct injection system was used for this study. Three sets of valve timing were selected to investigate the effect of intake valve opening duration. Experimental results demonstrated that an engine speed of approximately 2000rpm yields an NMEP (Net Mean Effective Pressure) range from 200kPa to 400kPa.

In this study, lean combustion concept was investigated to realize better Fuel Economy (FE) on a single cylinder motorcycle engine. A low-pressure direct injection (DI) system was applied to realize lean stratified combustion concept with good combustion stability. In addition, Exhaust Gas Recirculation (EGR) system applicable to small motorcycle engines was used to attain FE improvement and NOx reduction. EGR gas temperature and EGR return position were focused on and effects on FE and NOx were investigated. Computational Fluid Dynamics (CFD) was used to reveal EGR distribution and air motion in both the intake port and the cylinder. As a result, the influence of the stratified charge, EGR temperature and EGR return position on FE and NOx were explained quantitatively. These techniques were effective in reducing NOx and improving FE for a single cylinder motorcycle engine.

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.

Combustion phenomena inside the actual Gasoline-Direct-Injection (GDI) engines have been drawing high attention to its emission characteristics as well as its potential to deal with ultra lean mixture. Although the detailed observation is necessary for its improvement, combustion visualization seems to be strangely overlooked for some reason. This study focuses on the direct observation of GDI combustion to clarify the difficulties behind GDI concept by using a test engine of an actual “wall-guided” configuration and by comparing GDI spray quality with diesel spray in a high-pressure constant volume bomb. The results show that some of the problems about GDI combustion seem to be rather essential than easily conquered, which suggests the necessity for another combustion concept.

The in-cylinder flow, mixture distribution, combustion and exhaust emissions in a research, five-valve purpose-built gasoline engine are discussed on the basis of measurements obtained using laser Doppler velocimetry (LDV), fast spark-plug hydrocarbon sampling, flame imaging and NOx/HC emissions using fast chemiluminescent and flame ionisation detectors/analysers. These measurements have been complemented by steady flow testing of various cylinder head configurations, involving single- and three-valve operation, in terms of flow capacity and in-cylinder tumble strength.

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.

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 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.

With emergence of fuel cells which have much better thermal efficiency than internal combustion engines (later abbreviated as ICE), ICE has to improve its thermal efficiency to the level of 50%. One of the ways to improve the thermal efficiency of ICE is to utilize ultra-lean combustion and several technical papers have been published. But it seems the thermal efficiency has not been improved as the theory predicts. The test data of these technical papers were re-examined and it was concluded that the thermal dissociation of burned gas and NOx formation is the key factor of a discrepancy between the theory and the actual test data. In order to prevent an occurrence of thermal dissociation, emulsified fuels (mixture of carbonaceous fuels with water) was proposed.

In the past, the performance of motorcycle engines has improved quite rapidly through intensive competition in racing and in the marketplace. Motorcycle engines have contributed to the technological progress of internal combustion engines (hereafter abbreviated as ICE). Today's environmental concerns require motorcycle engines to improve fuel economy and exhaust emission pollutants. After examination of potential measures to improve the thermal efficiency of small engines, it was concluded that if engineers of motorcycle engines fail to take on new ideas such as those being developed in cold fusion, it is foreseen that motorcycle engines will be replaced with new power plants as was seen on locomotives in the past.

In recent years, global warming, depletion of fossil fuels, and reducing pollution have become increasingly prominent issues, resulting in demand for environmentally-friendly two-wheeled vehicles capable of reducing CO2 emissions. However, it remains necessary to meet customers’ expectations by providing smaller drivetrains, lighter vehicles, and support for long-distance riding, among other characteristics. In the face of this situation, hybrid electric vehicle (HEV) systems are considered to be the most realistic method for creating environmentally-friendly powertrains and are widely used. This research introduces a hybrid electric two-wheeled vehicle fitted with an electrical variable transmission (EVT) system, a completely new type of electrical transmission that meets the aforementioned needs, achieving enhanced fuel efficiency with a compact drivetrain. The EVT system comprises double rotors installed inside the stator.

In recent years, efforts to reduce CO2 emissions (carbon neutrality) have accelerated worldwide. In the aluminum manufacturing industry, CO2 emissions can be reduced by switching the raw materials of choice; from virgin ingots to recycled ingots. However, the possible characteristic change accompanying the usage of impurity-ridden recycled ingots severely limits its applications, which also limits its potential contribution to carbon neutrality. Determining how impurity elements present in recycled ingots can affect the function of manufactured components is a necessary first step towards expanding the usage of recycled ingots. In this study, we aimed to apply recycled ingots to the monolithic cylinder made of hypereutectic Al-Si alloy and investigated how impurity elements in recycled ingots affect properties (especially seizure characteristic). Die-cast cylinders using virgin and recycled ingots were manufactured and their properties were investigated.

This paper reports a methodology to estimate combustion pattern and emission by predictive simple simulation with good accuracy on various conditions of PFI engine. 3D-CFD cord VECTIS has been applied for this simulation, its settings and methods are as follows. RANS equation with liner k-epsilon model has been used as the turbulence model. Turbulent burning velocity equation contains not only turbulent velocity term but also laminar burning velocity term. For ignition model, we use a predictive model called DPIK. We iterate cycle calculation until wallfilm behavior is stabilized to get the reasonable mixture formation. We have applied this methodology to 125cc engine of motorcycle. As a result, we have obtained heat release curve and pressure curve with good accuracy on various operating conditions such as engine speed, engine load, air fuel ratio, wall temperature, and spray direction. CO and NOx calculated simultaneously have also been acceptable.

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.

Recently the response of the engine speed at starting has more importance than ever for quick start satisfying rider’s needs, as well as exhaust emissions. We have developed a simulation for studying engine and starter specifications, engine control algorithm and other engine control parameters. This system can be utilized to realize appropriate starting time by considering air-fuel ratio under various conditions. This paper addresses what are taken account of in our method. Examples applying this to a conventional motorcycle engine are shown.