Piston Crown Research Articles

On the Strength of Piston Crown of the Large marine Diesel Engine

Recently, special considerations must be taken for accidents caused by corrosion, wear and ther·mal stress in main parts of the large marine diesel engine because of the temperature increase of combustion gas resulting from the supercharge by the exhaust gas turbine and the utilization of bunker oil. Piston crown is one of the parts which have heavy local temperature rise and thermal stress as the result of exposure to this high temperature combustion gas. According to stress calculations, maximum stress of piston crown is generated at first piston ring groove and, at the working condition of the engine, the fluctuating stress by gas pressure is superposed to statical thermal stress. If these superposed stress is larger enough than yield strength of the material employed, the high residual stress in reversed direction occurs by the stop of the en gine. In this way the stress is repeated in reversed directions over the yield strength of the material in the worst case. We discussed a method of calculation of stress mentioned above and some points to be specially considered for the strength of machine parts which show such a complicated stress hysteresis.

Piston Assemblies for Road Transport Oil Engines

After reviewing the more usual types of piston failures such as breakage, seizure, ring sticking, land breakage, land scuffing, and groove destruction, means are suggested for their avoidance. There follows a consideration of the limiting factors of piston life, as indicated by the oil consumption of the engine. Dangers of overscraping new engines are emphasized and a method of retaining a minimum consumption over a long life is suggested. Examination of the rates of wear of the various components of the piston assembly leads to the conclusion that the top compression ring is the weakest point. Service test results with different piston ring materials are given and improved materials are suggested. Chromium-plated piston rings give the best results and are recommended for use as the upper compression ring. Finally, suggestions are given for designing the successful oil engine piston with a strong recommendation for the use of 12 per cent silicon alloy material and an adequate path for heat flow from the piston crown to the ring zone. Gudgeon-pin design is an important feature and design formulae are given. In summarizing, a model piston ring layout is given in detail.

Some Notes on the Mechanical Factors Affecting Ring Gumming in Petrol Engines with Particular Reference to the Rating of Lubricating Oils

The phenomenon of piston ring gumming in petrol engines is well known. It is of importance not only because it is the cause of considerable trouble in service, but it has also formed the chief criterion in the majority of attempts to rate or classify lubricating oils according to their deterioration characteristics in an engine cylinder. Existing standard chemical tests on lubricating oils form no guide to the behaviour of oils from the point of view of ring gumming in a petrol engine, and the only reliable method of grading oils at present is by tests in an actual engine. The next logical step is to develop a simple chemical test or series of tests which will give the same grading as that obtained in an actual engine. Before this can be done it is necessary to have a knowledge of the nature of ring groove deposits, the mechanism of ring gumming, and the relative effects of the various factors which affect the rate and degree of ring gumming. Mechanical factors can be of sufficient magnitude not only to affect, but possibly reverse, the relative rating of oils on a ring gumming basis. Various mechanical factors which affect the degree of ring gumming obtained are discussed in detail in the paper. Those mechanical variables which cannot be eliminated must either (1) be taken into account when sifting available engine data, or (2) must be a consideration when formulating a laboratory test or series of tests simulating engine conditions. Correlation between engine tests and laboratory tests is best based on the time to give incipient gumming in the engine. To do this it is necessary to have a reliable indicator to show when ring gumming commences. Preliminary experiments have indicated that piston-crown temperature is probably the best control temperature in oil rating tests; and the temperature at the back of the ring groove, taken in conjunction with the piston crown temperature, is probably the best indicator of incipient ring sticking capable of application to any engine.

Communications on Piston Crown Temperatures in a Compression-Ignition Engine with “Comet” Head

Communications on Piston Crown Temperatures in a Compression-Ignition Engine with “Comet” Head

Piston Crown Temperatures in a Compression-ignition Engine with “Comet” Head

The paper describes tests on a high-speed compression-ignition engine of 120 mm. bore fitted with a Ricardo “Comet” head in which the piston was of “Y” alloy. The temperatures were measured by thermocouples in the crown, the connexions to the temperature-measuring apparatus being intermittent, and made only when the piston approached bottom dead centre. Thermocouple voltages were measured on a potentiometer, using the “null deflexion” method. Piston crown temperatures were measured for various loads, speeds, and cylinder liner temperatures, and were found to be higher than those obtained in previous investigations because of the very high turbulence induced by the “Comet” type antechamber. Confirmatory tests were made by using temperature-indicating paints, but these were not as satisfactory as had been expected. The results are discussed in the light of knowledge gained in former work on this subject; and, in particular, comparison is made with temperatures obtained in tests on a Mirrlees-Ricardo sleeve valve engine of similar speed and using a piston of the same design and material.

Test for diethyl phthalate : Samuel Levinson ( Ind. and Eng. Chem., 1925, 17, 929)

This article presents a critical review of the studies performed to investigate combustion-chamber crevices as sources of hydrocarbon (HC) emissions, and an evaluation of potential technologies for reducing these emissions. Of the combustion-chamber crevices, the piston upper crevice volume is the main contributor to engine-out HC emissions. Chamfering the piston crown or reducing the top-land height and/or the volume behind the top compression ring may result in significant reductions in HC emissions. Modest reductions may also be achieved by reducing the central-electrode crevice of the spark-plug. However, reducing the head gasket crevice of current production engines appears to have little effect on engine-out HC emissions. In general, the sensitivity of the HC emissions to the combustion-chamber crevices is influenced strongly by the in-cylinder flow field and combustion, which influence the concentration of burned gases in the crevice gases.