## 3 Testing the RLE and BSL Single Cylinder Engines under Idle Conditions
### Extrapolation to a Complete Engine
If we assume that the total friction energy of the four-cylinder BSL in Table 3 is distributed among all 4 cylinders, and that the 100 units of friction energy corresponds to 137 kPa, one can calculate the predicted burden for the single cylinder BSL and RLE. The operating IMEP of the single cylinder BSL would be 137 kPa/100 \(\times\) 36.75 \(\times\) 4 = 201 kPa. The IMEP for the RLE would be 137/100 kPa \(\times\) 27.5 \(\times\) 4 = 150.7 kPa. Indeed, our IMEP calculation for BSL Case 1 is 208 kPa, while the RLE cases vary between 155 and 180 kPa. As discussed in Section 3.2, the IMEP numbers are not reliable due to the torsional vibrations that upset the volume calculation (likely more so for the RLE with the additional shaft portion that drives the rotating liner), but the order of magnitude IMEP seems to be in general agreement. The RLE seems to reduce the fMEP by about 50 kPa at idle. Since the boundary friction assembly term that the RLE minimizes increases at higher loads, the fMEP reduction will increase at these higher loads. We expect that future research will confirm that. Some researchers may find it difficult to believe that a piston friction reduction method can reduce total engine friction by 50 kPa or more. Part of the reason for this resistance is the many erroneous test results reported by the literature. While usually, the researchers mention that confidence in the absolute numbers of their reported fMEP is low and only the reported trends and margins are useful, nevertheless, readers tend to accept the numbers as given. [PERSON] et al. (2013) show (once corrected) that the piston assembly-loaded friction, plus unloaded piston assembly friction (boundary oil control rings and the hydrodynamic terms) and the valvetrain contribute 69 kPa for motoring conditions at the lowest rpm range. This graph is reproduced as Figure A6 in the Appendix A. [PERSON] et al. (2005) (2016), in a similar motoring tear down of the light-duty RLE and BSL engines, showed a friction reduction of 50+ kPa under motoring conditions. These motoring tests are relatively simple, so the confidence level in the absolute numbers is high. [PERSON] et al. (2017) presented two naturally aspirated spark ignition engines, one a conventional poppet valve, DOHC (dual overhead cam), and 4 valves per cylinder with stationary liners, and one a sleeve valve \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **4-Cylinder BSL** & **1-Cylinder BSL** & **1-Cylinder RLE** & **4-Cylinder RLE** \\ \hline Piston + valves 1  & 65 & 14.25 & 5.0 & 20 \\ \hline Crank & 10 + 10 1  & 2.5 + 10 & 2.5 + 10 & 10 + 10 \\ \hline Accessories & 15 & 10 & 10 & 15 \\ \hline Total & 100 & 36.75 & 27.5 & 55 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Hypothetical accounting of friction energy percentages at 750 rpm idle relative to the 4-cylinder BSL. The numbers for the 4-cyl. BSL are adjusted to reasonable numbers from the literature. The numbers for the 1-cyl. BSL are adjusted based on the components removed. The 1-cyl. RLE piston is reduced until the measured margin in friction is reached. Then, the RLE 4-cyl. contains the friction of the added components over the 1-cyl. RLE. This scenario shows a 45% reduction in 4-cylinder idle fuel consumption. (rotating cylinders close to TDC), both operating at a compression ratio of 6.5:1 and at wide open throttle (shown in Figure A8 in the Appendix A). The sleeve valve unit produced about 100 kPa more BMEP, even at a low engine speed where any possible advantage in volumetric efficiency of the sleeve valve cannot be significant. Note that the pressure loading of the piston rings of these two engines is not too far from our idling diesels, due to their very low compression ratio, even though they were operating at full throttle. Therefore, friction reduction of this order of magnitude, if indeed the boundary friction terms are minimized, is possible and consistent with the prior literature.