95,796 research outputs found
Investigation of combustion and performance characteristics of CAI combustion engine with positive and negative valve overlap
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.In the first part of studies, Controlled Auto-Ignition (CAI) combustion was investigated in a Ricardo E6 single cylinder, four stroke gasoline engine. CAI combustion is achieved by employing positive valve overlap configuration in combination with various compression ratios and intake air temperature strategies. The CAI operational region is limited by engine load due to knock and partial burned boundaries. The combustion characteristics and emissions are studied in order to understand the major advantages and drawbacks of CAI combustion with positive valve overlap.
The enlargement of the CAI operational region is obtained by boosting intake air and external EGR. The lean-boosted operation elevators the range of CAI combustion to the higher load region, and the use of external EGR allows the engine to operation with CAI combustion in the mid range of region between boosted and N/A CAI operational range. The results are analyzed and combustion characteristics, performance and emissions are investigated.
A Ricardo Hydra single cylinder, four stroke optical gasoline engine with optical access is then experimented to investigate CAI combustion through negative valve overlap configuration and an intake heater. The effects of direct fuel injection timings spark timings and air/fuel ratio are studied by means of simultaneous incylinder heat release study and direct visualization, chemiluminescence techniques which uses full, OH radical and CHO species. Both heat release analysis and chemiluminescence results have identified the pressure of minor combustion during the NVO period. Both the charge cooling and local air/fuel ratio effects are also investigated by varying the quantity of direct air injection
Performance and analysis of a 4-stroke multi-cylinder gasoline engine with CAI combustion
No full textCopyright © 2002 SAE International. This paper is posted on this site with permission from SAE International. Further use of this paper is not permitted without permission from SAEControlled Auto-Ignition (CAI) combustion was realised in a production type 4-stroke 4-cylinder gasoline engine without intake charge heating or increasing compression ratio. The CAI engine operation was achieved using substantially standard components modified only in camshafts to restrict the gas exchange process
The engine could be operated with CAI combustion within a range of load (0.5 to 4 bar BMEP) and speed (1000 to 3500 rpm). Significant reductions in both specific fuel consumption and CO emissions were found. The reduction in NOx emission was more than 93% across the whole CAI range. Though unburned hydrocarbons were higher under the CAI engine operation.
In order to evaluate the potential of the CAI combustion technology, the European NEDC driving cycle vehicle simulation was carried out for two identical vehicles powered by a SI engine and a CAI/SI hybrid engine, respectively. The simulation results showed only moderate improvement in fuel economy and exhaust emissions because of low utilisation of CAI during the drive cycle.
In order to take full advantage of the CAI combustion technology, detailed analyses were carried out on the engine’s performance, heat release and combustion characteristics, emissions and the effect of gas exchange processes. These analyses showed that the engine’s performance and emissions were mainly affected by the trapped residual fractions and residual temperature. In addition, the backflow was found to affect the combustion and emission as well
First-order system least squares for the Stokes and linear elasticity equations: Further results
No full textFirst-order system least squares (FOSLS) was developed in [SIAM J. Numer. Anal., 34 (1997), pp. 1727-1741; SIAM J. Numer. Anal., 35 (1998), pp. 320-335] for Stokes and elasticity equations. Several new results for these methods are obtained here. First, the inverse-norm FOSLS scheme that was introduced but not analyzed in [SIAM J. Numer. Anal., 34 ( 1997), pp. 1727-1741] is shown to be continuous and coercive in the L-2 norm. This result is shown to hold for pure displacement or pure traction boundary conditions in two or three dimensions, and for mixed boundary conditions in two dimensions. Next, the FOSLS schemes developed in [SIAM J. Numer. Anal., 35 (1998), pp. 320-335] are applied to the pure displacement problem in planar and spatial linear elasticity by eliminating the pressure variable in the FOSLS formulations of [SIAM J. Numer. Anal., 34 (1997), pp. 1727-1741]. The idea of two-dimensional variable rotation is then extended to three dimensions to make the intervariable coupling subdominant (uniformly so in the Poisson ratio for elasticity). This decoupling ensures optimal (uniform) performance of finite element discretization and multigrid solution methods. It also allows special treatment of the new trace variable, which corresponds to the divergence of velocity in the case of Stokes, so that conservation can be easily imposed, for example. Numerical results for various boundary value problems of planar linear elasticity are studied in a companion paper [SIAM J. Sci. Comput., 21 (2000), pp. 1706-1727].Z Cai: This author was sponsored by the National Science Foundation under grant DMS-9619792;
C.-O. Lee: This author was sponsored by BSRI-97-1436 and KOSEF 97-0701-01-01-3.
T. A. Manteuffel and S. F. McCormick: These
authors were sponsored by the National Science Foundation under grant DMS-9706866 and the Department of Energy under grant DE-FG03-93ER2516
New performing GC columns with unmatched separation capabilities
No full textGas chromatography (GC) is widely used for qualitative and quantitative analysis in numerous fields, such as petroleum, chemical industry, agriculture, environmental protection, medicine, and so on, due to its high
versatility, high selectivity, simplicity of use, analysis speed, and low sample consumption. The column is the heart of a GC instrumentation, which allows the analyte separation and their recognition and quantification. Commercial columns do not always allow a complete peak separation when compounds (i.e., isomers) are very
similar in molecular weight, polarity, and vapor pressure. The choice of the correct stationary phase, with high selectivity towards target analytes, is the key to obtaining the required chromatographic separation and the subsequent qualitative and quantitative analysis.
Considering the rapid polymer science development and the growing demand for new columns with
improved resolution capabilities, in this work novel stationary phases for capillary GC have been designed, synthesized, and characterized in terms of polarity range, resolution, column efficiency, thermal stability, filmforming properties, and support-deactivating capacity1-5. The separation features of these novel stationary phases allow high-resolution performances for a wide range of compounds, like aromatic anilines, xylenes, aromatic amines, halogenated benzenes, and aromatic aldehydes, with marked capabilities toward isomer separations.References:
[1] T. Sun, M. Ba, Y. Song, W. Li, Y. Zhang, Z. Cai, S. Hu, X. Liu, D. Nardiello, M. Quinto, Analytica Chimica Acta, 2024, 1291, art. no. 342221.
[2] T. Sun, R. Chen, Q. Huang, M. Ba, Z. Cai, H. Chen, Y. Qi, H. Chen, X. Liu, D. Nardiello, M. Quinto, Analytica
Chimica Acta, 2023, 1251, art. no. 340979.
[3] T. Sun, R. Chen, Q. Huang, M. Ba, Z. Cai, S. Hu, X. Liu, D. Nardiello, M. Quinto, ACS Applied Materials and Interfaces, 2022, 14 50, pp. 56132-56142
[4] R. Chen, Z. Cai, W. Li, Q. Huang, D. Nardiello, M. Quinto, X. Liu, S. Hu, T. Sun, Chemistry and Biodiversity, 2022,
19, art. no. e202200829
[5] Q. Huang, Z. Cai, R. Chen, W. Zhang, D. Nardiello, M. Quinto, X. Liu, S. Hu, T. Sun, Microchemical Journal, 2022,
183, art. no. 10808
Experimental studies of CAI combustion in a four-stroke GDI engine with an air-assisted injector
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.CAI combustion and the factors affecting it were intensively investigated in a single cylinder, air-assisted gasoline direct injection engine. CAI was achieved by means of residual gas trapping by utilising low-lift short duration camshafts and early closing of the exhaust valves. The effects of EVC (Exhaust Valve Closure) and IVO (Inlet Valve opening) timings, spark timing, single and split injection timings, coolant temperature, compression ratio, cam lift and duration on exhaust emissions and CAI operation were investigated experimentally. Engine speed throughout the course of the experiments, was varied from 1200rpm to 2400rpm and the air/fuel ratio was altered from stoichiometric to the misfire limit. The results show that the EVC timing, compression ratio, cam lift and duration had significant influences on CAI combustion and emissions. Early EVC when combined with higher compression ratio and higher cam lift, enhance CAI combustion operation and stability. IVO timing had minor effect on CAI combustion while spark timing hardly affects CAI operation as soon as fully-developed CAI conditions were established. Coolant temperature was revealed to have substantial impact on CAI combustion when the coolant temperature was below 65oC. The results also show the importance of injection timing. Early injection gave faster and more stable combustion, less HC and CO emissions, but more prone to knocking combustion and higher NOx emissions. Furthermore, CAI operation range could considerably be extended with injection during the recompression process. Late injection led to slower and unstable combustion, higher HC and CO emissions but lower combustion noise and NOx emissions. Split injection gave even further extension of CAI range in both stoichiometric and lean mixture operations. All the above clearly suggest, that optimising injection timing and using split injection is an effective way to control and extend CAI operation in a direct injection gasoline engine
Phosphorylation of PDHA by AMPK drives TCA cycle to promote cancer metastasis-Zhen Cai
No full textRaw gel for Phosphorylation of PDHA by AMPK drives TCA cycle to promote cancer metastasi
Investigation of transition between spark ignition and controlled auto-ignition combustion in a V6 direct-injection engine with cam profile switching
No full textControlled auto-ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI) can be achieved by trapping residuals with early exhaust valve closure in a direct fuel injection in-cylinder four-stroke gasoline engines (through the employment of low-lift cam profiles). Due to the operating region being limited to low and mid-load operation for CAI combustion with a low-lift cam profile, it is important to be able to operate SI combustion at high-load with a normal cam profile. A 3.0L prototype engine was modified to achieve CAI combustion, using a Cam Profile Switching mechanism which has the capability to switch between high and low-lift cam-profiles. A strategy was used where a high-profile could be used for SI combustion and a low-lift profile was used for CAI combustion. Initial analysis showed that for transitioning from SI to CAI combustion, misfire occurred on the first CAI transitional cycle. Subsequent experiments showed that the throttle opening position and switching time could be controlled avoiding misfire. Further work investigated transitioning at different loads and from CAI to SI combustion
Experimental investigation of gasoline – Dimethyl Ether dual fuel CAI combustion with internal EGR
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.A new dual fuel Controlled Auto-Ignition (CAI) combustion concept was proposed and researched for lower exhaust emissions and better fuel economy. The concept takes the advantage of the complementary physical and chemical properties of high octane number gasoline and high cetane number Di-Methyl Ether (DME) to organize the combustion process. Homogeneous gasoline/air mixture is utilized as the main combustible charge, which is realised by a low-cost Port Fuel Injection (PFI) system. Pressurised DME is directly injected into cylinder via a commercial Gasoline Direct Injection (GDI) injector. Flexible DME injection strategies are employed to realise the controlled auto ignition of the premixed charge. The engine is operated at Wide Open Throttle (WOT) in the entire operating region in order to minimize the intake pumping loss. Engine load is controlled by varing the amount of internal Exhaust Gas Recirculation (iEGR) which is achieved and adjusted by Positive Valve Overlap (PVO) and/or exhaust back pressure, and exhaust rebreathing method. The premixed mixture can be of either stoichiometric air/fuel ratio or fuel lean mixture and is heated and diluted by recycled exhaust gases. The use of internal EGR is considered as a very effective method to initiate CAI combustion due to its heating effect and moderation of the heat release rate by its dilution effect. In addition, the new combustion concept is compared to conventional SI combustion. The results indicate that the new combustion concept has potential for high efficiency, low emissions, enlargement of the engine operational region and flexible control of CAI combustion
Higgs-Z-photon coupling from effect of composite resonances
No full textWe explore the Higgs-Z-photon coupling in the Minimal Composite Higgs Model with vector and axial resonances. The electroweak precision measurement, i.e. S and T, is estimated for this model. We calculate the signal strength for Higgs decay into Z-photon and notable enhancement is found in certain EWPT allowed parameter region.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000334449700001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Physics, Particles & FieldsSCI(E)[email protected]
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