Shibata, G., Nakayama, D., Okamoto, Y., and Ogawa, H., "Diesel Engine Combustion Noise Reduction by the Control of Timings and Heating Values in Two Stage High Temperature Heat Releases," SAE Int. J. Engines 9(2):868-882, 2016, doi:10.4271/2016-01-0731.
Reductions in combustion noise are necessary in high load diesel engine operation and multiple fuel injections can achieve this with the resulting reductions in the maximum rate of pressure rise. In 2014, Dr. Fuyuto reported the phenomenon that the combustion noise produced in the first combustion can be reduced by the combustion noise of the second fuel injection, and this has been named “Noise Cancelling Spike Combustion (NCS combustion)”.To investigate more details of NCS combustion, the effects of timings and heating values of the first and second heat releases on the reduction of overall combustion noise are investigated in this paper.The engine employed in the research here is a supercharged, single cylinder DI diesel engine with a high pressure common rail fuel injection system. The engine was operated at 2000 rpm and 0.8MPa IMEP, and the structural attenuation of the test engine was calculated from the power spectrum of the FFT analysis of the in-cylinder pressure wave data and the cross power spectrum of the sound pressure of the engine noise by the coherence method. With the heat release history approximated by the Wiebe function, the pressure history could be calculated from the heat release history, and the simulated combustion noise was calculated from the pressure history and structural attenuation. The test parameter variables are the combustion duration of crank angles of 10% burns in the first and second high temperature heat releases (CA101-2), the duration of the peaks of the maximum rate of pressure rise (dP/dθ1-2), and the heating values of the first and second fuel injections (Q1st and Q2nd). The effects of these parameter variables on the combustion noise were investigated. Simulations showed that the combustion noise was the minimum when the dP/dθ1-2 was 7.4 °CA, and that 4.1 dBA of combustion noise could be reduced by the NCS combustion, and this was verified by the engine tests. In the simulations, with the CA101-2 = 8 °CA and Q1st:Q2nd = 350J:450J, the overall combustion noise was the minimum, and further, the optimum heat release shape for the higher thermal efficiency and lower combustion noise are suggested in the paper.