[vex]

As promised:

Apex Seal: Early in the development stage the RE used a composite one-piece apex seal made of carbon impregnated with aluminum. It was replaced later by a two-piece apex seal to provide better gas sealing, with the material changed to a stronger one in the form of cast iron.

The top surface of this apex seal that slides on the chrome plating shown in Fig. 8 is melted by electron beam and rapid solidified to provide an approximately 3mm chilled layer.

The chilled layer has excellent anti-friction properties since it contains a crystallization of finer cementite than is obtainable by ordinary chill casting. The base metal of the apex seal is accicular cast iron with bainitic structure. In addition to offering high strength and ductility to the apex seal, this structure gives increased wear resistance to its side faces (where it contacts with the apex seal groove walls) and its end faces (where it contacts with the side housing).

Apex Seal Temperature - Since lubrication between apex seal and trochoid is an important factor of engine operation, it was necessary to learn the apex seal's temperature distribution during operation with respect to oil film formation.

The amount of necessary lubricant for the lubrication between apex seal and trochoid surface has a close relation to the apex seal temperature, as shown in Fig. 9.

The suitable amount of the lubricant is that of when apex seal temperature begins to rise up due to the lack of the lubricant.

From this point of view, the apex seal temperature was measured to know how the temperature changes during engine running.

Apex seal temperature measurement was conducted by the following procedure...(omitted because it's not necessary for discussion)...[list=1][*]Temperature of bottom and top of Apex Seal - Temperature was measured at the top and bottom of the apex seal: as shown in Fig. 11, the temperature of the apex seal rises in accordance with the engine revolution, however at 5000 RPM with high load the apex seal temperature is reduced, because the combustion gas temperature is reduced by setting of richer mixture at high load. The temperature difference between top and bottom was below 10*C as shown in Fig. 11.[*]Apex Seal's Axial Temperature - Temperature was taken at the middle and both ends of the apex seal as shown in Fig. 12. It is to be noted that the heat flux into the seal flows to the side housing and rotor housing, indicating that the heat transmitted to the side housing exceeds the heat transmitted to the trochoid surface because of wider contact area of the end surface of the apex seal.[*]Temperature in Transient Condition - Fig. 13 plots temperatures that the apex seal registered when the engine was accelerated from 1000 RPM under no load up to 5000 RPM WOT and held at this speed for 45 seconds before it was decelerated to 1000 RPM under no load.

At 1000 RPM at no load, the apex seal's top was lower in temperature but became hotter during acceleration, and during deceleration it became less hot than the bottom.

If this is to be believed the main issues of expansion and contraction as well as heat flow is going to be through the side plates.

From the same report:

Side Housings: The side housing's inner wall is rubbed by the corner seal, side seal, oil seal, and rotor flank. This associated rubbed surface is in face contact and represents a considerable bearing area, with relatively generous supply of lubricating oil. Thus the side housing's operating condition is favorable compared to the rotor housing's.

However, as the engine is made capable of higher speed and power output, the thermal load rises, causing its operating condition to become less favorable, with the result that the oil seal lip in particular suffers increased wear, thus increasing oil consumption. To solve such problems, the plain cast iron surface of the side housing was softnitrided with resultant improvement in wear resistance and anti-corrosion.

(I'm putting in large portions so individuals can decide for themselves)

I'll work on getting some of the figures posted up for everyone's benefit. But just looking at them I see something rather interesting; As load is increased both BMEP and temperature peak at 4000 RPM and both begin to decrease proportionately to HP rating from 4k RPM to 5k RPM. If I'm understanding this correctly it correlates perfectly with what has been stated by others here.

Burning super lean even in low load conditions will increase the instantaneous heat in the chamber as well as the heat transfer into the combustion face material (as can be seen in another figure showcasing why iron wasn't used for the rotor housing).

Given the nature of the defects and what the SAE paper has stated concerning a stock configuration it can be intimated that failure of the Apex Seals is going to be derived from lean conditions increasing the heat of the combustion chamber beyond design constraints. The result; heavy thermal loading of metalic parts.

To tackle thermal expansion and any subsequent interference from the Apex Seal and side housings will need to be evaluated on merit (I will actually be attempting a simulation here shortly to test just that).