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We experimentally investigated effects of pilot diesel-fuel injection on ignition timing variation and noise reduction in a diesel engine with hydrogen addition to the intake pipe. The pilot diesel-fuel injection suppressed ignition timing variation which was significant under hydrogen addition conditions. The heat release by the pilot diesel-fuel injection stably acted as an ignition source of the hydrogen-air mixture. The maximum in-cylinder pressure rise rate increased with the hydrogen fraction. However, the sound pressure level attained minimum around a specific hydrogen fraction.

We experimentally investigated the influence of shifting natural frequencies of the internal transmission system depending on the connecting-rod specifications on the characteristics of noise radiated from a single-cylinder diesel engine. We used FFT analysis to investigate the influence of shifting natural frequencies of the internal transmission system on the radiated noise characteristics. By changing the thinned portion of the connecting-rod, we confirmed that the natural frequency of the piston-connecting-rod-coupled vibration differed from another natural frequency of the engine structure, and thus the engine noise was reduced. This research studied the time-frequency characteristics of combustion impact and engine noise by wavelet analysis of in-cylinder pressure and sound pressure.