Torsional Vibration Reduction for Geared Aviation Compression Ignition Engines with Power Transmission Through the Camshaft or Dedicated Internal Driveshaft A Sweep Through 2 and 4-Stroke Engines with Differing Numbers of Cylinders and Two Comparison Power Train Configurations Indicate the 4-Stroke, 6-Cylinder Engine is Ideally Suited for this Application 2017-01-1808

In a previous report, it was shown that power transmission through the camshaft reduced the first mode natural frequency of the power train and translated its convergence with dominant engine excitatory harmonics to a lower engine speed resulting in a marked reduction in torsional vibration while achieving 2/1 gear reduction for a 4-stroke 6-cylinder compression ignition (CI) engine 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) or an equivalent dedicated internal driveshaft (DISE). Four and 6-cylinder 4-stroke engines were modeled as opposed boxer engines. Four and 6-cylinder 2-stroke engines and 8, 10 and 12-cylinder 2-stroke and 4-stroke engines were modeled as 180° V-engines. All 2-stroke engines were considered to be piston ported and configured as SGRE or DISE. All 4-stroke engines were configured as SGRE or CDSE. Mass-elastic models of the different engine power train configurations were constructed and analyzed using the torsional vibration module in Shaft Designer obtained from SKF (Svenska Kullagerfabriken). Maximum torsional stress at the power train segments was used to discriminate between the different configurations. The best 4-stroke CDSE configuration was the 6-cylinder engine as described previously and provided a significant advantage over the SGRE configuration. The best 2-stroke applications with the analogous DISE configurations were the 8 and 10-cylinder engines although they were inferior to the SGRE configurations. These simulation studies suggest that the 6-cylinder 4-stroke engine is ideally suited for use with the CDSE power train configuration for reduction of torsional vibration and achieving gear reduction compared with SGRE.