Donald J. Patterson

MEASUREMENT OF PISTON AND RING ASSEMBLY FRICTION INSTANTANEOUS IMEP METHOD

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. To date the technique has been used only for low speed engine operation.

Effect of Some Lubricant and Engine Variables on Instantaneous Piston and Ring Assembly Friction

The Instantaneous IMEP method has been used to measure piston and ring assembly friction in a production Chevrolet 1.8 litre L-4 and a 5 litre V-8 engine modified for single-cylinder operation. Friction measurements are reported at different loads and speeds up to 1640 RPM under firing and motoring conditions with various oils and before and after break-in of the oil ring. Oils used were SAE viscosity grades 30, 50 and 30 with a friction modifier. Differences were found between motoring and firing friction, especially on the power and exhaust strokes. These differences diminished at higher speeds and lower loads where lubrication was more hydrodynamic. Differences in response to viscosity and friction modifier changes were noted between the two engines.

Effect of some piston variables on piston and ring assembly friction

The piston and ring assembly friction of a lightweight piston with lower compression height has been compared to that of a production assembly. Additional weight was added to the lightweight piston to study the effect of that variable alone. The lightweight piston reduced friction, especially in motoring tests. Within the speed range tested (up to 1640 rpm) the friction reduction of the lightweight piston could not be attributed to the lower mass itself.

Piston and Ring Friction by the Fixed Sleeve Method

A new technique termed the «fixed sleeve» method has been developed to measure the instantaneous friction of the piston and ring assembly as a function of crank angle. This method is a derivative of what has been termed the «moveable bore» method. Results are presented for friction determinations on a 4.1 litre gasoline engine for motoring and firing operation at a variety of speeds, loads, and engine temperatures

Oil and Ring Effects on Piston-Ring Assembly Friction by the Instantaneous IMEP Method

This paper describes the friction characteristics of a 1.8 Litre J-car piston and ring assembly as influenced by oil rings of conventional design, but of varying tensions. In addition, the piston-ring assembly friction characteristics are reported for a set of oil viscosities ranging from 2 to 20 cSt with and without a molybdenum friction modifier. Multigrade oil results are shown also. Finally comparisons are presented between changes in friction measured by the Instantaneous IMEP Method and those measured by the dynamometer for the engine as a whole.

Modeling and Experimental Determination of the Axisymmetric Flow in a Diesel Engine Cylinder

Internal air motion in a Detroit Diesel 6V-92 two-stroke engine cylinder was determined by an idealized axisymmetric finite difference model under steady flow conditions. This model was used to compute axial and tangential velocities with entrance angles of 25 and 40 deg. Laser Doppler anemometer measurements were made in one plane for comparison under steady flow bench test conditions using actual engine hardware. Calculations and measurements showed that the swirl induced by the angled inlet flow was responsible for the nonuniform axial velocity profiles. These profiles exhibited large peaks in the midradius region (between cylinder center and wall). Increasing the inlet angle from 25 to 40 deg sharpened the axial velocity peak and shifted it toward the cylinder wall. The measurements indicated nearly isotropic turbulence across the measurement plane. A better understanding of the relationship between design and internal flow is expected to lead to improved combustion, scavenging tradeoffs.