Wakuri Yutaro

Studies on the Mixed Lubrication of Piston Rings

A great deal of attention has been focused on decreasing the piston assembly friction in piston engines, since this friction acounts for the majority of total mechanical power loss in these type of engines. The tribology of the sliding surfaces between piston rings and cylinder liner includes extremely complicated phenomena which will become even more severe with an increase in the engine power. In the present study, the theoretical analysis on the mixed lubrication of piston rings is made. The analysis is comprised of Patir and Chengs average flow model and Greenwood and Tripps asperity interaction model, and is developed to consider the shear thinning effect of non-Newtonian fluid, multigrade oil. The friction characteristics of piston rings for both monograde and multigrade oils are investigated and compared with experimental results obtained by the floating liner method, which can measure the instantaneous friction force of a piston assembly under firing conditions.

Exhaust Emissions from Marine Diesel Engines Using Residual Fuel

Recently the air pollution caused by marine diesel has become a more serious problem. For such engines heavy fuel, e. g. bunker fuel oil, is usually used. High residual portion and long ignition delay are the main disadvantage of heavy fuel. Their effects are especially severe at low load, which is the running condition of ships near the seashore where the pollution is a more serious problem.In this study the emission from a relatively high speed marine diesel engine using heavy fuel is examined. Because the effects caused by heavy fuel can be observed more clearly on a high speed diesel engine, such one was used for the experiments instead of a low speed engine.The experiments show clearly that heavy fuel causes higher smoke density than gas oil. The higher smoke density is caused by direct impingement of the unevaporated residual portion onto the piston.On the other hand the effect of heavy fuel on NOx emission can not be explained simply, because it is influenced by two counteracting effects : the higher pre-mixed combustion rate, which increases NOx formation, and the later ignition timing, which decreases it.

Studies on Measurement Method of Total Friction Loss of Internal Combustion Engines

In the present study, a new test method is investigated to measure the total friction loss of engines over the entire ranges of speed and load. It is based on the idea that the friction loss close to the actual one of fired and braked engines can be measured by the run-out method because the temperature condition influencing the friction loss is nearly stable for the short test duration after the fuel cut. From the test results and the comparison with those measured by other conventional test methods, the following become evident. (1) The frictional mean effective pressure increases slightly as the revolution speed increases, but it decreases as either the load or the cooling water temperature increases. (2) The frictional mean effective pressure measured by the present method is smaller than that measured by the run-out mothod, the motoring method or Willans line method, but it is larger than the one measured by the indicated pressure diagram method.

Studies on the Characteristics of Piston Ring Friction. Influences of Oil Properties.

In reciprocating internal combustion engines, one of the most important issues is to clarify the frictional characteristics between the piston ring and the cylinder liner because of the demand for reduction in frictional loss as well as the solution to problems such as scuffing and wear with the advances in engine performance achieved in recent years. In the present study, the floating liner method in which the cylinder liner is supported by means of hydrostatic bearings was developed to measure accurately the frictional force of the piston assembly as a function of the crank angle during firing operation. The influences of engine operating conditions (engine speed, cylinder wall temperature, gas pressure in the cylinder), lubricating oil viscosity, polymer-containing multigrade oil and friction modifier on the frictional characteristics were evaluated on the basis of the experimental results obtained with this equipment.

Experimental Studies on Friction Characteristics of Cam/Tappet

The reduction of friction and wear of cam/tappet interfaces in the valve gear mechanism is effective to improve the performance and reliability of internal combustion engines. Lightweight, antiwear materials such as ceramics seem applicable to the tappet, so it is necessary to study the tribological characteristics. In the present study, the frictional force between the cam and tappet is directly measured using a load sensor installed in a test rig, and the following is carried out. Firstly, the changes of friction with valve spring load, camshaft revolution speed and oil temperature are examined for current materials and CD-level oil of diesel engines, and their empirical relations with the coefficient of friction or frictional mean effective pressure are investigated. Secondly, the influence of oil contamination is examined for the oil used. Lastly, the friction characteristics of the ceramic tappet of silicon nitride, silicon carbide and sialon are obtained, and the influence of surface roughness and the running-in effect of rubbing are clarified.

Lubrication of a Crosshead-Pin Bearing in a Two-Stroke Cycle Engine : Analysis for the Case of an Elliptical Bearing Surface

The crosshead-pin bearing equipped with axial oilgrooves in a two-stroke cycle diesel engine cannot produce such a thick oilfilm as to hold the bearing to be always free from troubles since the bearing is subjected to high load in a single direction besides a low speed. This paper refers to a theoretical analysis on the lubrication of a crosshead-pin bearing with an elliptical bearing and a circular journal. This bearing can remarkably increase the oilfilm thickness and is superior to the conventional bearing in load-carrying capacity and oilfilm exchanging ability as the wedge film action greatly increases due to the presence of two converging-diverging film shapes in load-carrying film.

An Experimental Study on the Fuel Spray Distribution and Combustion in a Direct-Injection Typed Diesel Engine

流入スワ-ル強度可変機構を設けた単流掃気形二サイクルディーゼル機関を使用した実験から、燃焼に最適なスワ-ルの強さは、噴射ノズルの噴口数だけでなく、噴霧の衝突条件や燃焼室形状、また燃焼性状によっても変化することがあきらかとなった。またビストンに設けた皿を深くすることによって、噴口数が少ない場合の排煙濃度を改善でき、皿の形状を変えることによって、さらに燃焼改善をはかる自由度があることも確かめられた。