Fig. 12 Shafting stress within barred speed range: combustion starts at +25 deg. ATDC, unrefined injection law
Fig. 13 Cylinder pressure: 6RTA62 engine, 48 rpm, 20% load, pilot injection at TDC, main combustion starts at +25 deg. ATDC
Fig. 14 Tangential pressure Fourier Analysis: 6RTA62 engine, 48 rpm, 20% load, Pilot injection at 0 deg. -TDC, main combustion starting +25 deg. ATDC
Fig. 15 Cylinder pressure, Heat release, Cylinder temperature, 6RTA62 engine, 48 rpm, pilot injection BTDC, main combustion starts at +25 deg. ATDC
From this data can be easily seen that as the engine load goes higher on the propeller law, the 6th harmonic component amplitude for "standard engine settings" has an increasing trend, compared with the +25 deg. ATDC combustion start, where the pressure trace Fourier analysis showed a decreasing trend for the 6th harmonic amplitude. The amplitude for the 6th harmonic component with the "new" setting is approx. 3 times lower than the original one that caused the allowable stress to be exceeded at the resonance. These results have not only the advantage of a low excitation amplitude but also a simplified injection management due to the fact that all optimised excitations are obtained for the same combustion timing: +25 deg. ATDC, despite the load and speed variation. The phase of the 6th order vectors versus the combustion timing is in the range from approx. -10 deg. to -30 deg. the only out of range for all three speeds being that at +30 deg. ATDC combustion starting, with a value of approx. +20 deg. These values doesn't support again the belief that with different injection timing in each cylinder the different phasing of vectors could decrease the torsional deformation and stress drastically for this particular application (Fig. 11).
