Abstract
The Rotating Liner Engine (RLE) concept is a design concept for internal combustion engines, where the cylinder liner rotates at a surface speed of 2–4 m/s in order to assist piston ring lubrication. Specifically, we have evidence from prior art and from our own research that the above rotation has the potential to eliminate the metal-to-metal contact/boundary friction that exists close to the piston reversal areas. This frictional source becomes a significant energy loss, especially in the compression/expansion part of the cycle, when the gas pressure that loads the piston rings and skirts is high. This paper describes the Diesel RLE prototype constructed from a Cummins 4BT and the preliminary observations from initial low load testing. The critical technical challenge, namely the rotating liner face seal, appears to be operating with negligible gas leakage and within the hydrodynamic lubrication regime for the loads tested (peak cylinder pressures of the order of 100 bar) and up to about 10 bar BMEP (brake mean effective pressure). Preliminary testing has proven that the metal-to-metal contact in the piston assembly mostly vanished, and a friction reduction at idle conditions of about 40% as extrapolated to a complete engine has taken place. It is expected that as the speed increases, the friction reduction percentage will diminish, but as the load increases, the friction reduction will increase. The fuel economy benefit over the US Heavy-Duty driving cycle will likely be of the order of 10% compared to a standard engine.
Highlights
The Rotating Liner Engine (RLE, www.rotatingliner.com) is a unique lubrication concept aimed at Diesel engines, where the cylinder liner rotates to eliminate the boundary friction environment for the piston rings and skirt around the TDC of compression-expansion
Sci. 2021, 11, 779 necessarily represent the actual friction. Another factor that limits the accuracy of floating liner testing is the fact that the state of wear of the cylinder liners and piston rings is generally in the close to new condition with the honing marks still fresh, and the piston ring profile is still mostly intact as it was optimized by its designers
It can be assumed that the indicated thermal efficiency of both engines is about identical, and since the only load on the engine at idle is its own internal friction, the fMEP is directly proportional to the heat needed to sustain the engines. This total heat release per cycle is proportional to the PCP-peak motoring pressure (PMP), as long as the comparison is made for cases where about the same percentage of the total heat release is complete at the TDC, and/or as long as the peak cycle pressure is around the TDC
Summary
The Rotating Liner Engine (RLE, www.rotatingliner.com) is a unique lubrication concept aimed at Diesel engines, where the cylinder liner rotates to eliminate the boundary friction environment for the piston rings and skirt around the TDC (top dead center) of compression-expansion. It is well understood from the literature that this specific form of friction loss is responsible for a substantial portion of the mechanical losses in Diesel engines (especially at high loads). The observed considerable increase in FMEP (friction mean effective pressure) as a function of engine load can be traced mostly to this particular factor and it is responsible for the principal wear mechanism that limits engine life
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