180

CRANK ANGLE (DEG)

Figure 14. Cylinder pressure (upper), strain gauge (center), and resulting friction force. WOT, 1000 rpm, motoring.

Each engine presents a different challenge in so far as designing and applying the Fixed Sleeve method. Figure 15 shews a design created for the Cummins 903. At the left is a collar which is rigidly attached to the underside of the block. That collar has a necked-down section with strain gauges mounted inside and outside. The collar and liner bottom are both threaded. The liner is then inserted into the block and screwed in to the collar which supports it rigidly at the bottom. The top of the liner is specially prepared as a separate piece shown on the right in the figure. This piece is clamped to the block by the cylinder head in the same manner as the production engine. The liner and the top piece have a concentric step, and are allowed to slip relative to each other. Seeding is accomplished by two o-rings. Combustion gases are sealed by a metal o-ring. Rubber o-rings axe used to isolate coolant from the metal combustion seal ring area.

Figure 15. Fixed Sleeve design for Cummins 903 engine.

At this time it is not known whether the Fixed Sleeve method will be satisfactory in the 903 engine without further modification. Its virtues are that the strain gauge instrumentation is attached neither to the piston or liner, and consequently either piston or liner can be replaced without disturbing the instrumentation. Also the instrumentation is located away from the major heat source and could be cooled as required. This is expected to be a plus for the uncooled diesel. Finally errors in the cylinder pressure measurement are less of a problem since the pressure correction involves forces acting on the rim area rather than the entire piston crown as is the case in the Instantaneous IMEP method. Finally there are no inertia forces to take into account. The next step is to complete the fabrication of the Fixed Sleeve method for the 903 engine and evaluate it.

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