Takehiko Seo

A study on transient noise-generation characteristics in a diesel engine with rapid premixed-charge compression ignition combustion

This study investigates time-frequency characteristics of noise generation in a diesel engine with rapid PCCI (premixed-charge compression ignition) combustion. We increased the pilot injection quantity from a base PCCI condition to simulate rapid PCCI combustion. We measured the in-cylinder pressure and sound pressures and analyzed them using fast Fourier transformation and wavelet transformation. The main cause of the engine noise is the combustion impact on the combustion chamber. We clarified the process that the combustion impact vibrates the engine structure and then lead to sound radiation. We identified main frequencies, whose noise components largely affect the overall level of engine noise. Almost all engine noise components at the main frequencies were found to be strongly affected by the combustion impact. We researched the noise source and transmission path of each noise component by using a sound field visualization device and measuring accelerations on the engine surface.

Sound source identification on automotive muffler surface using single explosion excitation and near-field acoustic holography method

Recent automobiles tend to have larger interior space, resulting in the smaller space for arranging the muffler. Flat shape mufflers are required for this reason but cause relatively large radiation noise from the surface. In order to improve understanding of radiation noise generation mechanism of flat shape muffler, we tried to identify the noise sources using the near-field acoustic holography (NAH) method on muffler surface excited by a single explosion pulse, which simulates a single pulsation in the exhaust system,. Two types of mufflers were tested with different shapes. Results show that some areas had large vibration velocity at specific frequencies depending on the muffler shape. The flat muffler tends to generate large radiation noise and vibration velocity as compared with a conventional one. In the front and rear outer plates of the muffler, large vibration velocity exists within a certain range of frequency. Within the same frequency range, the flat muffler has more number of the peak of rad...

A Study on Ignition Characteristics of Rich-Premixed Ethanol Spray by Laser-Induced Plasma

Laser-induced breakdown and ignition of rich-premixed ethanol spray were studied using a Nd:YAG laser. The ignition characteristics in liquid fuel spray were investigated comparing the experimental result of different phases of fuel.

The Influence of Hydrogen Addition to Diesel Fuel Spray Combustion for Different Atomization Conditions

The negative effects of hydrocarbon fuels are widely highlighted by increasing global warming and declining quality of human health. Therefore, it is important to reduce the level of emissions from liquid hydrocarbon combustion. Hydrogen addition to the combustion chamber is one of the proven methods to improve emssions level. In this research, an experiment was conducted on diesel fuel spray combustion with hydrogen addition. The effect of additional hydrogen was observed on CO, CO2, NO and THC exhaust gas emissions. A small hydrogen fraction (0~3 vol %) was added to the rich premixed spray combustion. The results show that increasing the hydrogen fraction reduced the emission indexes of CO and THC, and increased the emission index of CO2. Increasing the hydrogen fraction caused an increase in the emission index of NO, but the actual physical amount was insignificant. Increasing the atomizing air flow rate reduced the CO and THC emission indexes, but increased the CO2 and NO emission indexes.