1. |
-
- 2019
-
Journal article (peer-reviewed)
|
|
2. |
- He, Shuai Feng, et al.
(author)
-
Multi-scale dynamics for a lean-burn spark ignition natural gas engine under low load conditions
- 2023
-
In: Fuel. - : Elsevier BV. - 0016-2361. ; 332
-
Journal article (peer-reviewed)abstract
- This work investigates the multi-scale dynamics of the combustion system in a lean-burn spark ignition natural gas engine using different gas injection timings (GIT). The in-cylinder pressure time series are measured, and the indicated mean effective pressure (IMEP) time series are calculated. The influence of GIT on the combustion system is investigated through wavelet analysis, multi-resolution analysis, and the return maps with the GIT covering from 0 to 90°CA after top dead center at the intake stage. Results show that the combustion system has multi-scale chaotic characteristics, and it is sensitive to the change of GIT. The unreasonable GIT will result in serious combustion variations. Meanwhile, the combustion instability of the engine evolves on multiple time scales, showing evident multi-scale oscillation characteristics. All the wavelet power spectrums (WPS) present the characteristics of intermittent short-time periodic oscillations and persistent large-scale periodic oscillations concealed inside the IMEP time series. When the GIT approaches the medium value, the persistence of large-scale periodic oscillations is weakened, while the characteristics of high-frequency intermittent oscillations are enhanced. Under all working conditions, the contribution rate of high-frequency signal D1 decomposed by the IMEP time series to the overall time series fluctuation is about 40% or even higher. The contribution rate of the signal D1 also increases with the aggravation of combustion instability. The return map structures of high-frequency signals D1 and D2 show bifurcation structures, and the bifurcation characteristics of the signal D1 are more evident under medium GIT conditions, indicating a certain correlation between the 2–8 engine cycles, and the correlation between the adjacent engine cycles is stronger. The deterministic relationship between the multiple engine cycles found can help in developing a more reasonable and efficient combustion control strategy, which provides a theoretical basis for improving the stability of a natural gas engine.
|
|
3. |
- Ding, Shun Liang, et al.
(author)
-
Analysis of the fractal characteristics for combustion instability in a premixed natural gas engine
- 2023
-
In: Applied Thermal Engineering. - 1359-4311. ; 233
-
Journal article (peer-reviewed)abstract
- To investigate the influence of gas injection timing (GIT) on the combustion instability of a premixed natural gas engine, experiments were conducted under low load conditions using various GITs. Multifractal and multiscale entropy analyses were employed to examine the fractal characteristics and complexity of the experimental time series for indicated mean effective pressure (IMEP) and heat release (Q) at different scales. Statistical analysis and return maps of the IMEP and Q time series were utilized to verify the results. The findings revealed that the combustion process of the natural gas engine demonstrates clear fractal characteristics at different scales. A strong correlation is found between the combustion instability and the fractal characteristics. Furthermore, the probability densities of the IMEP and Q time series exhibit super-Gaussian distributions. Retarding the GIT results in an initial increase, followed by a decrease in the difference value of the Hurst index and singular spectrum width. The mapping point distributions of the IMEP and Q time series initially disperse and subsequently concentrate. The fractal complexity and chaotic characteristics of combustion instability initially strengthen and then gradually diminish. Moreover, under lower load conditions, the anti-persistent correlation becomes more pronounced, and the intermittence and complexity of the fractal characteristics also intensify, signifying a more significant impact of GIT on the combustion instability of the natural gas engine. Notably, when the GIT is approximately 60°CA after top dead center, the combustion process exhibits stronger fractal characteristics, accompanied by a greater dispersion degree of the mapping points. This study provides a theoretical basis for enhancing the lean-burn stability of natural gas engines.
|
|
4. |
- Wu, Kuan-Hsun, et al.
(author)
-
Considerations of SiP based Antenna in Package/Module (AiP/AiM) Design at Sub-Terahertz Frequencies for Potential B5G/6G Applications
- 2021
-
In: Proceedings - Electronic Components and Technology Conference. - 0569-5503. ; 2021-June, s. 1162-1168
-
Conference paper (peer-reviewed)abstract
- Antenna-in-Package/Module (AiP/AiM) are the primary technologies to realize the RF subsystems for frequencies beyond millimeter-wave (mmW) bands, including sub-terahertz for potential B5G/6G applications. Due to the small wavelength, the mechanical process of the current system-in-package (SiP) results in limitations to realize antenna arrays at sub-terahertz. In this paper, the mechanical limits to cause radiation discrepancy is investigated by designing an AiP/AiM at 110 GHz band. Through the parametric studies based on the currently available cheap SiP process, one may summarize the considerations of AiP/AiM design for beyond sub-terahertz frequencies. The examination will consider the design of an 8x8 antenna array to provide a radiation gain of 20 dBi. Numerical full-wave simulations by HFSS were performed to obtain reliable behaviors of AiP/AiM radiations.
|
|