## 3 Testing the RLE and BSL Single Cylinder Engines under Idle Conditions
### Extrapolation to a Complete Engine  
In this section, we will describe a friction energy accounting scenario, in order to extrapolate the potential reduction in the idle fuel economy of a complete 4 BT, if we had indeed converted all cylinders, and we were comparing the 4-cylinder RLE to a complete 4-cylinder baseline engine. Figure 17 shows the conceptual CAD of a multi-cylinder RLE. In this CAD representation, all the design features of the rotating liner components as fabricated for this prototype are reproduced so that the performance characteristics of this prototype would be perfectly duplicated without any changes, and would fit in the existing block. Table 3 shows a likely percentage distribution of component friction for the original Cummins 4 BT, and how the RLE reduces it, in order to approximate the measured friction reduction via analysis of the combustion characteristics of the two single cylinder engines. The numbers assigned fit general friction distributions that are reported in the literature. Note also, according to a motoring tear down friction test of a diesel engine published by [PERSON] (2013), at 750 rpm, the piston assembly (plus valves, but the valvetrain is a small contributor) was the dominant source of friction by about 75% of the total, so the Table 3 numbers may be a bit conservative concerning the piston assembly's contribution (note, [PERSON]'s graph does not properly assign the removal of the cylinder head to the piston assembly; this is a typical error in published tear down tests, which are often performed in the wrong order, [PERSON] 2019). The units in Table 3 are arbitrary, adjusted to give 100% for the 4-cylinder BSL. In the column that corresponds to the 4-cylinder BSL, the crank \(10+10\) corresponds to 10% for the connecting rod bearings and 10% for the main bearings. The accessories include the injection pump, which will have a substantially reduced power requirement when operating on one cylinder. All injection pump pistons accept fuel during engine operation, but only one piston compresses the fuel against the injector--the other three pistons just return the fuel to the tank without compressing it. The piston assembly contribution for the RLE single cylinder was reduced until the RLE single-cylinder total friction was about 25% reduced from the single cylinder BSL and so as to be consistent with the measurements presented above. The result is a total friction reduction of over 40%. The numbers in Table 3 illustrate that the measured 25% friction reduction in the single-cylinder RLE will receive a considerable amplification when a complete four-engine is converted. The dramatic piston assembly friction reduction in Table 3 from 14.25 to 5.0 is consistent with the tear  
Figure 17: CAD representation of the multi-cylinder RLE. The critical components are identical to the current prototype, and the model of the block is the production engine, so a direct modification is feasible. down presented by [PERSON] et al. (2005), where a similarly dramatic friction reduction was recorded for the light-duty RLE under motoring conditions. The fMEP shown by [PERSON] (2013) is about 105 kPa, but this is a motored condition which is known to yield reduced fMEP. The fMEP of a regular diesel at firing idle at the above coolant temperature is about 137 kPa, based on the friction model by [PERSON] (1965) and presented again by [PERSON] (2012), updated with coefficients that are a better match for modern engines. The calculation used the mid-range of all coefficients except for the hydrodynamic term, which we used the highest value, justified by the relatively low coolant and oil temperature. The above friction model is semi-empirical and calibrated to match a large number of experimental datasets by Southwest Research Institute. The calibration was performed in the late 1990s when the Cummins 4 BT engines were being tested and built. Based on our information, Cummins is currently using a similar model with coefficients of about similar values.