| 1. |
- Fang, Cheng, et al.
(författare)
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Closed-loop combustion phase control for multiple combustion modes by multiple injections in a compression ignition engine fueled by gasoline-diesel mixture
- 2018
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Ingår i: Applied Energy. - : Elsevier BV. - 0306-2619. ; 231, s. 816-825
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Tidskriftsartikel (refereegranskat)abstract
- Partially premixed combustion with low octane fuel aims to reduce NOx and soot emission simultaneously without fuel consumption penalty. Cylinder pressure based combustion phase control is an essential technology for partially premixed combustion. A novel closed-loop combustion phase control strategy for multiple combustion modes is proposed in the current study. The combustion modes are classified into three basic categories based on injection patterns and heat release stages: (1) with only one heat release stage; (2) with two separated heat release stages; (3) with two overlapped heat release stages. Crank angle when 50% fuel is consumed (CA50) is chosen as the combustion phase indicator for the first case. Start of combustion (SOC) of each heat release stage is the combustion phase indicator for the second case. Both SOC and CA50 are the combustion phase indicators for the third case. Each combustion phase is closed-loop controlled by a proportional–integral (PI) controller with the timing adjustments of the corresponding injection. The control strategy is verified under different operating conditions in a 1.9 L light duty diesel engine fueled by gasoline-diesel mixture (volumetric 70% gasoline, 30% diesel). The experimental results show that the control strategy is able to control the combustion phase, reduce cylinder to cylinder variations as well as cycle to cycle variations under the operating conditions with exhaust gas circulation (EGR) rates of 10% and 15%.
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| 2. |
- Fang, Cheng, et al.
(författare)
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Start of low temperature reactions detection based on motoring pressure prediction for partially premixed combustion
- 2018
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 141, s. 1101-1109
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Tidskriftsartikel (refereegranskat)abstract
- Partially premixed combustion aims to reduce NOx and particulate matter emission without fuel consumption penalty. Low temperature reactions are important for the partially premixed combustion. In the current study, a self-adaptive strategy is introduced to predict the motoring pressure by means of an equivalent isentropic index. The start of the low temperature reactions is detected when the pressure difference between the measured pressure and the predicted pressure is higher than a threshold value. Experimental results show that the maximum variation between the measured and the predicted motoring pressure before the top dead center is less than 0.02 bar. It is also demonstrated that the presented detection method is able to detect the start of the low temperature reactions under different engine operating conditions with varying injection timing, injection duration, number of injections and exhaust gas recirculation rate.
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| 3. |
- Fang, Cheng, et al.
(författare)
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Study on low temperature heat release of partially premixed combustion in a heavy duty engine for real-time applications
- 2019
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 148, s. 219-228
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Tidskriftsartikel (refereegranskat)abstract
- Partially premixed combustion aims to reduce NOx and particulate matter emission without fuel consumption penalty. Low temperature heat release (LTHR) is an important process to be investigated. A novel motoring pressure prediction algorithm based on variable polytropic exponents was introduced and utilized to estimate average heat transfer coefficient as well as heat dissipation for real-time applications. A series of parameters, such as start of combustion (SOC) of LTHR, crank angle of 50% heat released (CA50) during LTHR, duration of LTHR and heat amount of LTHR, were further analyzed under different engine operation conditions. The results demonstrated that: (1) the absolute motoring pressure prediction error was below 0.5 bar with a relative error below 4%; (2) the average heat released during LTHR was about 40–65 J, and the mass burned was about 1–3% of the total mass burned; (3) CA50 of LTHR was more stable than SOC of LTHR, and was a better indicator for real-time combustion phase control; (4) similar combustion phase and heat amount of LTHR could be reached by adjusting the timing of the third injection regardless the difference in timing of the second injection; (5) the combustion phase and heat amount of LTHR could be controlled by the duration of the second injection.
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| 4. |
- Yang, Junhuai, et al.
(författare)
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Holocene forcing of aeolian dust activity over the Tibetan Plateau and its surroundings
- 2024
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Ingår i: Global and Planetary Change. - 0921-8181 .- 1872-6364. ; 235
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Tidskriftsartikel (refereegranskat)abstract
- Aeolian deposits on the Tibetan Plateau (TP) and its surroundings provide crucial source materials for the Asian dust cycle, which significantly affects Asian and global ecosystems and climate. However, it is unclear how the dust dynamics of the TP and its surroundings are linked to Earth's climate system. To address this issue, we examined the grain size and accumulation rate of six Holocene aeolian sections on the southern TP (a new, well-dated high-resolution section, two relatively low-resolution sections, and three published sections) and combined them with equivalent aeolian sedimentary records from eastern arid central Asia. The results suggest that dust activity in both regions decreased during the early to middle Holocene and then increased in the late Holocene. We hypothesize that the primary drivers of Holocene dust activity in both regions are similar. Cold-season insolation, as the primary driving factor, combined with ice volume and atmospheric CO2 concentration, collectively controlled the regional temperature, which determined the near-surface wind intensity via its influence on the TP High and Siberian High, respectively, thus ultimately controlling the regional dust activity. In this context, we project that dust activity on the TP and its neighboring areas will decrease under warm scenarios in the 21st century. Overall, our findings provide an extensive overview of the past, present, and future scenarios of Asian dust activity, especially of the TP dust.
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| 5. |
- Gao, Fuyuan, et al.
(författare)
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Rapid retreat of the East Asian summer monsoon on the western Chinese loess Plateau during the middle to late Holocene and its environmental and societal implications
- 2023
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Ingår i: Catena (Cremlingen. Print). - 0341-8162 .- 1872-6887. ; 231
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Tidskriftsartikel (refereegranskat)abstract
- Spatiotemporal changes in the Holocene climate of the arid region of China were principally caused by shifts in the intensity and location of the East Asian summer monsoon (EASM). However, our knowledge of these EASM variations is limited, especially since the middle Holocene. We investigated two aeolian sedimentary sections (the Linxia/LX and Gulang/GL sections) on the western Chinese Loess Plateau (CLP), to explore the variations in the intensity and location of the EASM and their impact on the regional environment and human cultural development during the middle to late Holocene. The longitudes of these two loess sections are similar, but the GL section is located on the northern edge of the CLP, in the eastern Hexi Corridor, and it is situated further north than the LX section. The chronologies of both sections are based on accelerator mass spectrometry C-14 dating, and environmental magnetic parameters and grain size end-members were used to reconstruct their moisture histories. The results suggest that the climate at the LX section was relatively dry before 3.5 ka, after which it became wetter. In contrast, at the GL section, the climate was also relatively dry before 3.5 ka, with the wettest conditions occurring during 3.5-2 ka, but subsequently there was an abrupt shift to a dry climate. We suggest that these spatiotemporal patterns reflect the westward movement and rapid southward retreat of the EASM and the linked monsoon rainfall belt. TraCE-21 ka climate simulation results support our inference. We also found that, compared with other ancient cultures in the eastern Hexi Corrido, sites of the Shajing culture, dated to similar to 2.4-2.8 ka, are predominantly located in areas that are arid at the present-day, and relatively distant from rivers. We suggest that this distribution pattern reflected the occurrence of a humid climate during the period of the Shajing culture, thus demonstrating the impact of the EASM on cultural development in this region.
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