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A semi-empirical engine piston/ring assembly friction model based on the concept of the Stribeck diagram and similarity analysis is described. The model was constructed by forming non-dimensional parameters based on design and operating conditions. Friction data collected by the Fixed-Sleeve method described in [1]* at one condition, were used to correlate the coefficient of friction of the assembly and the other non-dimensional parameters. Then, using the instantaneous cylinder pressure as input together with measured and calculated design and operating parameters, reasonable assembly friction and fmep predictions were obtained for a variety of additional conditions, some of which could be compared with experimental values. Model inputs are component dimensions, ring tensions, piston skirt spring constant, piston skirt thermal expansion, engine temperatures, speed, load and oil viscosity.

Cylinder pressure variation is a fundamental and widespread combustion problem in spark-ignited engines. The basic factors causing this problem are variations both in the start and in the rate of combustion. These variations occur not only from cycle to cycle within each cylinder but may also show up as consistent differences between cylinders. Our test results indicate that the major cause of cyclic combustion rate variation is the mixture velocity differences that exist within the cylinder near the spark plug at the time of ignition. As yet we do not know how to reduce the cyclic mixture velocity variations and thus reduce the problem at its origin. However, it is possible to circumvent some effects of cyclic pressure variation by increasing the average combustion rate.

Air motion in one cylinder of a Detroit Diesel 6V-92 two stroke diesel engine was studied under steady flow bench test conditions by a laser Doppler anemometer and an axisymmetric finite difference fluid dynamic model. The effects of four different exhaust opening geometries were explored. Measurements and calculations showed that the swirl induced by the 18 angled inlet ports produced non-uniform axial velocity profiles and large peaks in the mid-radius region (between cylinder center and wall). The exhaust opening geometry in the head of the cylinder influenced these axial velocity fields especially in the upper region of the cylinder. The study concluded that more uniform flow, which is favorable to the scavenging process, can be achieved by an exhaust opening located close to the cylinder periphery.

An experimental technique termed the Instantaneous IMEP Method has been developed to measure piston and ring assembly friction. The technique requires very accurate measurements of cylinder pressure, connecting rod force and calculation of inertial forces. Friction force is the difference of these forces in consideration of the slider-crank geometry. A grasshopper linkage has been used to transmit the connecting rod force signal measured by a strain gage bridge. Inertial forces have been calculated with the assumption of distributed connecting rod mass. The test engine was a Chevrolet 5 litre V-8, modified for single cylinder operation. Piston and ring assembly friction has been determined under motoring conditions with and without compression as well as firing. Friction measurements have been made with SAE 30 and 50 grade oils at different temperatures. Boundary friction has been observed especially near top and bottom dead centers.

Typically, engines with relatively few cylinders have required higher cranking speed to start in low temperature ambients. Of the several factors that contribute to cold startability, this study has focused on the instantaneous speed variation of the engine during cranking. This theoretical computer study revealed that engines slow substantially during compression and that the lengthening of compression time is exaggerated as the number of cylinders is reduced. It is hypothesized that long compression time creates excessive heat and blowby losses. In turn these produce low compression temperatures and pressures, hence greater difficulty in igniting the charge especially under cold cranking conditions were average engine speed is low, By matching the compression times of various engines designs, the relative average speeds required to start can be predicted with reasonable accuracy.

A new bench tester for laboratory simulation of piston ring and cylinder wear has been developed. Tests are made using liner segments which bear against a reciprocating piston ring. Temperatures up to 550°C, and loads and speeds representative of the most severe top ring conditions may be imposed. A precision oil spray system delivers the desired quantity and quality of oil to the wear interface. The computer controlled simulator duplicates the desired test cycle, and displays and stores data on friction forces and friction coefficients as the test proceeds. In this paper results are presented from the simulator for production and prototype ring and liner combinations, including ceramic coatings for potential use in advanced diesel engines. The importance of the method of oil delivery on test repeatability is emphasized. Some comparisons with Cameron Plint bench tests and firing engine results are presented.

This paper presents an overview of techniques for measuring friction using bench tests and fired engines. The test methods discussed have been developed to provide efficient, yet realistic, assessments of new component designs, materials, and lubricants for in-cylinder and overall engine applications. A Cameron-Plint Friction and Wear Tester was modified to permit ring-in-piston-groove movement by the test specimen, and used to evaluate a number of cylinder bore coatings for friction and wear performance. In a second study, it was used to evaluate the energy conserving characteristics of several engine lubricant formulations. Results were consistent with engine and vehicle testing, and were correlated with measured fuel economy performance. The Instantaneous IMEP Method for measuring in-cylinder frictional forces was extended to higher engine speeds and to modern, low-friction engine designs.