Torsional Vibration Reduction in Compression Ignition Engines for Aviation: A sweep through 2 and 4-Stroke Engines with differing Numbers of Cylinders and Powertrain Configurations.

Paper #:
  • 2017-01-1808

Published:
  • 2017-06-05
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Abstract:
In a previous report, it was shown that power transmission through the camshaft reduced the first mode natural frequency of the powertrain and translated its convergence with dominant engine excitatory harmonics to a lower engine speed resulting in a marked reduction in torsional vibration for geared 6 cylinder compression ignition engines for aviation. This report describes a sweep though 2 and 4 stroke engines with differing numbers of cylinders configured as standard gear reduction (SGRE) and with power transmission through the camshaft (CDSE). Four and 6 cylinder engines were modeled as opposed boxer engines and 8, 10 and 12 cylinder engines were modeled as 180-degree V-engines. Mass-elastic models of the different engine power train configurations were modeled using the torsional vibration module in Shaft Designer obtained from SKF (Svenska Kullagerfabriken). Crankshaft, camshaft, gearing, pistons, piston pins and connecting rods with bolts were modeled in Solidworks. Mass, mass moments of inertia and component dimensions were obtained from the modeled components in Solidworks. Camshaft section stiffness was calculated from area polar moments of inertia based on shaft section internal and external diameters, lengths and modulus of rigidity. Crankshaft section stiffness was calculated from area polar moments of inertia based on equivalent solid shaft lengths of main journal diameter calculated according to Ker Wilson 1956, Practical Solution of Torsional Vibration Problems, Wiley, New York, Volume 1, and modulus of rigidity. Gear stiffness was calculated using formulas from Nestorides, E. J., 1958, A Handbook on Torsional Vibration, Cambridge University Press, New York. Damping was applied as internal damping to each shaft segment and gears and assigned as 1.59% of critical damping. Maximum torsional stress at the powertrain segments was used to discriminate between the different configurations. The best 4-stroke CDSE configuration was the 6-cylinder engine as described previously and the worst 4-stroke application was in the 4-cylinder engine. The best 2-stroke applications of the CDSE configuration were in the 8 and10 cylinder engines and the worst application in the 4-cylinder engine. These simulation studies provide further guidance for uses of the CDSE powertrain configuration for reduction of torsional vibration in aviation diesel engines.
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