Gas Blowby Research Articles

Implementation of an Algorithm to Model the Starved Lubrication of a Piston Ring in Distorted Bores: Prediction of Oil Flow and Onset of Gas Blow-By

Experimental evidence suggests that piston rings in internal combustion engines normally experience 'starved' lubrication at some points along their stroke. To take account of lubricant starvation (and hence move towards a full ring pack analysis), a 'flow continuity algorithm' has been incorporated into a non-axisymmetric lubrication model of a single ring. The algorithm allows both inlet and cavitation boundaries of the full film to be located, making it possible to predict the occurrence of gas blow-by through the ring face, particularly for distorted bores. In addition, oil availability has been determined by applying the principle of mass conservation while considering lubricant accumulation. The computational scheme has been tested extensively and, in consequence, its credibility has been confirmed. Using this approach, a piston ring in a non-circular bore has been studied. The results show that, in general, the operating performance of the ring is influenced significantly by lubricant starvation. In particular, as starvation increases, the conditions that could lead to gas blow-by are greatly enhanced.

3-D Measurement And Visual CharacterisationOf Cylinder Liner Bore Polishing

Wear in engine cylinder liners has long been a problem which has attracted considerable attention over the past 50 years. The surface of the liner is usually generated by a combination of base and plateau honing. The honed surface serves a dual function of providing good bearing capability as well as the ability to retain lubricant. Excessive wear can lead to the removal of the honing grooves and the formation of polished regions. These areas, known as bore polish, are detrimental to the overall performance of the engine and can lead to gas blow-by and scuffing. The engine testing industry, as part of their criteria for determining the performance of a lubricant, will inspect an engine liner for the size and frequency of these polished regions. The inspection of bore polish is a long and tedious process carried out by an inspector peering over the liner block with a torch and tracing the outline of polish regions onto an acetate sheet. There are numerous sources of errors and problems associated with this technique. In order to provide to provide a better insight into bore polishing the School of Manufacturing and Mechanical Engineering, in collaboration with an independent engine testing laboratory, investigated this phenomenon. This paper will describe the current inspection technique and introduce a method of visually characterising the degree of bore polish. In an attempt to quantify the polish categories recently-developed 3-D surface characterisation techniques were employed.

Cylinder Bore Wear

The author has been responsible for the design of engines for a motor car in which the life of the cylinder bore over a period of ten years and a total of eight million engines is 12,000 miles per 0·001 inch wear. The factors contributing to this result are as follows: (1) thermostatically controlled cooling for water at a minimum temperature of 145 deg. F., preferably 160 deg. F.; (2) crankcase ventilation to eliminate the effects of blow-by in the oil sump; (3) adequate oil supply to cylinder bores; (4) complete control of the lubricant at the piston rings, not at the source of supply of the oil; (5) control of gas blow-by at the rings; (6) leanest possible mixture ratios for general operating conditions; (7) close attention to the type of fuel used to ensure that it is properly vaporized; (8) a uniform hot metal temperature; and (9) an accurate spark advance mechanism. All these factors are discussed by the author in detail, special attention being paid to the testing of piston rings in the laboratory, the correct use of thermostats, and crankcase scavenging.