## 2 The Heavy-Duty RLE Prototype  
### Selected Pictures from the Diesel RLE Prototype  
This section presents pictures of the prototype. The actual CAD of the prototype was presented by [PERSON] et al. 2012 [5]. Relatively minor design changes have been made, and many of these will be pointed out in this section. Both baseline and RLE started life as a four-cylinder Cummins 4 BT 3.9 model year prior to 1998 (two valves per cylinder, mechanical fuel injection). Both are converted to single-cylinder operation. The overall layout of the RLE prototype can be seen in Figure 4. Cylinder #2 is the only active cylinder, and all other three crank throws are covered by bob weights that block oil leakage and also rebalance the crankshaft. The brass driving gear on the position of cylinder #1 engages the crankshaft via an external level 90-degree gearbox and belt with a total gear reduction of about 2.7:1 (later, when detailed testing was performed, the ratio was reduced to 3:1). This driving gear is identical in diameter and number of teeth to the rotating liner flange gear; therefore, it could be replaced by an actual rotating liner if the engine was to be a complete four-cylinder (proposed driving mechanism is shown by [PERSON] et al. 2012). However, now two bearing holders are secured on the untouched original engine bore, and these bearings support the vertical shaft that is shown in Figure 4. The shaft goes through the cylinder head and engages the bevel gearbox discussed above. Figure 5 shows the details of the face seal features on the rotating liner flange. These are exactly as described by [PERSON] et al. 2012. The face has been flattened by lapping to the tolerance level of typical face seals, which is of the order of 1 micron flatness or less, and was also polished. There are nine oil supply holes across the flange which feed oil to the annular groove. The annular area inside the annular groove is called the \"sealing zone\" (see [PERSON] 2012) [5] and acts as a sealing dam and squeeze film bearing. The etched step pads are visible, and these constitute the primary hydrodynamic features. The primary sealing ring can also be seen, held by a human hand. The primary sealing ring is actually flat (the radial marks seen are from the oil, which is deposited in an uneven manner, replicating the pattern from the rotating liner features that it was in contact with). The head gasket is a 2.25 mm (0.090 inch)-thick copper unit (identical gasket used in the baseline). In the case of the RLE, the head gasket only seals coolant and oil, so the head bolts need not be torqued down to the full 90 ft-lbs required by the Cummins shop manual. Figure 4: Block of the RLE diesel prototype. The driving gear could be replaced by another rotating liner, so the engine could operate as a complete four-cylinder 4 BT RLE. Figure 5: Details of the rotating liner face seal features. The copper head gasket only needs to seal oil and coolant. This picture is shown again in the Appendix A with a higher resolution. Figure 6 shows the block with the cylinder head removed, the rotating liner pulled out to expose the polished outside surface. The brass thrust washer on the head block is visible. This thrust washer is loaded by the spring load acting on the primary sealing ring. However, as discussed by [PERSON] et al. (2012) [5], when the engine is started and oil pressure is restored, the oil pressure will take the load and this thrust washer will no longer be active. The bearing holder for the driving gear shaft but without the ball bearing used is also visible on the bottom left of the picture (the driving gear has been removed). Figure 7 shows the cylinder head with the head insert and primary sealing ring springs (component terminology follows [PERSON] et al. 2012). This part is built out of mild steel and houses the secondary seal and springs, as described by [PERSON] et al. 2012 [5]. The only deviation from the [PERSON] et al. (2012) description is that conventional coil springs are used in place of a conical washer spring due to cost considerations.