The Influences of Connecting-Rod Specifications on the Combustion Noise Generation from a Diesel Engine 2019-01-1590
Recently, premixed-charge compression ignition (PCCI) is attracting attention due to its low exhaust emission in diesel engines. However, PCCI leads to a great combustion noise which limits the operation range. Therefore, combustion noise reduction is necessary to extend the PCCI operation range.
We investigated the influence of shifting natural frequencies of the internal transmission system, which depend on the connecting-rod specifications on the radiated noise characteristics by the FFT analysis. We confirmed that by changing the thinned portion of connecting-rod, the natural frequency of the piston-connecting-rod-coupled vibration became different from another natural frequency of the engine structure, and thus the engine noise was reduced.
Nguyen et al. proposed a time-frequency-dependent combustion noise generation model. This model considers that the vibration energy of each frequency component is accumulated in the engine structure excited by the combustion impact during the combustion period in a cycle and decays over time, and combustion noise radiates from the engine surface. This model suggests that the maximum engine noise power has a linear relation to the maximum combustion energy and the gradient of the graph is proportional to the vibration-transmission efficiency from the combustion impact to the engine surface vibration. The shift of natural frequencies of the internal transmission system will change the vibration transmission path, in other words, the vibration-transmission efficiency.
We experimentally investigated the influence of shifting natural frequencies of the internal transmission system depending on the connecting-rod specifications on the radiated noise characteristics from a single cylinder diesel engine. We obtained time-frequency characteristics of combustion impact and engine noise by wavelet analysis of in-cylinder pressure and sound pressure. We discussed the vibration transmission characteristics for two different connecting rod through the relationship between the maximum engine noise power and the maximum combustion energy in the same cycle for main frequencies of combustion noise.
Hitoshi Oguchi, Koki Minato, Takehiko Seo, Masato Mikami
Noise and Vibration Conference & Exhibition