A modified exhaust valve timing (earlier close) in order to increase the real compression ratio of the engine and the compression temperature also. The adjusted valve timing is possible to increase not enough the compression temperature and some other solutions should be employed.
Another solution (in conjunction or not with the first one) would be a pilot injection earlier in the cycle (around TDC) when the fuel would self-ignite and would enable (despite all the heat loses) to maintain the charge temperature high enough for the main late injected quantity of fuel to self-ignite too. It should be pointed out, that the engine new settings and modifications should be active only for less than 10 seconds, during the pass through the barred speed range.
Table 3 Amplitude of the 6th harmonic versus engine speed and combustion start
Fig. 11 The phase of the 6th harmonic of tangential pressure with the combustion timing: 6RTA62 engine, 44 rpm, propeller law
7. FOURIER ANALYSIS OF THE TANGENTIAL PRESSURE
The Fourier analysis of the tangential pressure obtained from the cylinder pressure trace, showed invariably the same trend:
for +25 deg. ATDC combustion starting, for all investigated speeds, the excitation amplitude of the 6th order harmonic component has the smallest level from all the combustion timings: [-30 deg. BTDC...+30 deg. ATDC].
These results are plotted in Fig. 7, 8, 9, 10 and Fig. 14. Table 3 shows the differences between "standard" and "new" engine setting for the 6th order harmonic amplitude behavior:
