10 % Fuel Economy Benefit at Part Load and up to 33 % at Idle for a Diesel Engine via Reducing Friction. Testing the Rotating Liner Engine and an Identical Baseline Under Load

The Rotating Liner Engine (RLE) is a design concept where the cylinder liner of a heavy-duty Diesel engine rotates at about 2-4 m/s surface speed to eliminate the piston ring and skirt boundary friction near the top and bottom dead center. Two single cylinder engines are prepared using the Cummins 4BT 3.9 platform, one is RLE, the other is baseline (BSL), i.e. conventional. In 2022, we published the test results of the RLE under load, but we lacked detail test data for the baseline. In this new set of experiments, we compare the RLE performance at idle and under load of up to about 7 bar IMEP (indicated mean effective pressure) to the baseline under similar conditions. It has been proven that the elimination of metallic contact between the compression rings and cylinder wall takes place with a liner speed of 1.5-2.3 m/s surface speed (283-426 rpm for the 102 mm bore) for the 850-1280 rpm crankshaft speed. The RLE FMEP is substantially reduced under load, which is a trend opposite to standard engines.

The total reduction of FMEP for idle and medium load is measured to be 0.4 and 0.8 bar respectively. When the above results are applied to complete rather than single cylinder engine application, the combined fuel efficiency benefit is approximated to a fuel consumption reduction of 33 % at idle and up to 10 % for medium loads and speeds. Minimization of cylinder and piston ring wear is expected. One significant observation from the research is that the piston rings and skirt boundary friction is a dominating factor in the friction losses of the modern diesel engine. We have not yet operated the two engines under forced air induction, but we expect the RLE benefit to be approximately double the 0.8 bar measured benefit of the naturally aspirated engines. Extrapolating the experimental results to a 20 bar BMEP bring fuel economy improvement to over 7 %