1,962,919 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
Combustion characteristics of CAI combustion with alcohol fuels
No full textSAE paper 2010-01-0843: Copyright © 2010 SAE International. This paper is posted on this site with permission from SAE International, and is for viewing only. Further use and distribution of this paper is not permitted without permission from SAE.Due to its potential for simultaneous improvement in fuel consumption and exhaust emissions, controlled autoignition (CAI) combustion has been subject to continuous research in the last several years. At the same time, there has been a lot of interest in the use of alternative fuels in order to reduce reliance on conventional fossil fuels. Therefore, this experimental study has been carried out to investigate the effect of alcohol fuels on the CAI combustion process and on the resulting engine performance.
The experimental work was conducted on an optical single cylinder engine with an air-assisted injector. To achieve controlled autoignition, residual gas was trapped in the cylinder by using negative valve overlap and an intake air heater was used to ensure stable CAI combustion in the optical engine. Methanol, ethanol and blended fuels were tested and compared with the results of gasoline. The combustion processes were analysed through total chemiluminescence images captured with a high speed camera equipped with an intensifier. In addition, the effect of spark discharge was investigated.
The images show that CAI combustion of alcohol fuels was characterized with fast and early autoignition combustion compared with pure gasoline. Chemiluminescence of the gasoline fuel was most visible and it decreased with increasing percentage of oxygenated fuels. During the re-compression stroke, chemiluminescence images of the gasoline engine indicated the presence of oxidation reactions. In the presence of spark discharge, the location of charge ignition was dominated by spark discharge at the center of cylinder while simultaneous autoignition sites were found around the periphery of the combustion chamber for non-spark-assisted ignition
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
Rifugi montani sentinelle del clima e dell'ambiente : Un progetto CAI - CNR che si estende dalle Alpi al Mediterraneo
Get PDFNasce una Rete di Rifugi CAI e di Osservatori CNR che percorre tutta la penisola con lo scopo di mettere a sistema infrastrutture già esistenti in aree praticamente incontaminate al fine di ottenere un quadro reale ed aggiornato sullo stato del clima e dell’ambiente sulle nostre montagne.Mountain refuges sentinels of the climate and the environment - A CAI (Italian Alpine Club) - CNR (National Research Council) project that extends from the Alps to the Mediterranean
A network of CAI Refuges and CNR Observatories is born that runs throughout the peninsula with the aim of setting up existing infrastructures in practically uncontaminated areas in order to obtain a real and upda- ted reference of the state of the climate and the environment in our mountains
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
CAI combustion with methanol and ethanol in an air-assisted direct injection SI engine
No full textCopyright © 2009 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 SAECAI combustion has the potential to be the most clean combustion technology in internal combustion engines and is being intensively researched. Following the previous research on CAI combustion of gasoline fuel, systematic investigation is being carried out on the application of bio-fuels in CAI combustion. As part of an on-going research project, CAI combustion of methanol and ethanol was studied on a single-cylinder direct gasoline engine with an air-assisted injector. The CAI combustion was achieved by trapping part of burnt gas within the cylinder through using short-duration camshafts and early closure of the exhaust valves. During the experiment the engine speed was varied from 1200rpm to 2100rpm and the air/fuel ratio was altered from the stoichiometry to the misfire limit. Their combustion characteristics were obtained by analysing cylinder pressure trace. The experimental results show that both oxygenate fuels, methanol and ethanol, can lead to CAI combustion as well as gasoline fuel. The load of CAI combustion was increased and emissions were lower with the two oxygenate fuels. Methanol was found to have highest output and lowest energy consumption among the three fuels tested. CAI combustion characteristics of the oxygenate fuels were more affected by the amount of burnt residuals trapped than that of gasoline fuel
Fòrum debat: Arquitectura i tècnica. 20 anys del Departament de CAI (1a part)
No full textForum debat: arquitectura i tècnica es celebra el divendres 29 de febrer de 2008 commemorant els 20 anys del Departament de Construccions arquitectòniques (CAI)a la Sala d’actes de l’edifici Vèrtex del campus Nord.Primera part del "Foro Debat: arquitectura i tècnica" amb una presentació del director del Departament de CAI Joan Lluís Zamora Mestre i Josep Lluís González-Barroso i diverses intervencions de convidats
Concrete Crack images for segmentation
No full textThis is a concrete crack dataset for segmentation. It is partially from Ozgenel FÇ. Concrete crack segmentation dataset. Mendeley Data 2019; 1: DOI: 10.17632/jwsn7tfbrp.1. and @article{liu2019deepcrack, title={DeepCrack: A Deep Hierarchical Feature Learning Architecture for Crack Segmentation}, author={Liu, Yahui and Yao, Jian and Lu, Xiaohu and Xie, Renping and Li, Li}, journal={Neurocomputing}, volume={338}, pages={139--153}, year={2019}, doi={10.1016/j.neucom.2019.01.036}}If the dataset helps your research, please cite our paper:@article{xie2022sparse, title={Sparse-sensing and superpixel-based segmentation model for concrete cracks}, author={Xie, Xiongyao and Cai, Jielong and Wang, Haozheng and Wang, Qiang and Xu, Jieying and Zhou, Yingxin and Zhou, Biao}, journal={Computer-Aided Civil and Infrastructure Engineering}, year={2022}, publisher={Wiley Online Library}
Fòrum debat: Arquitectura i tècnica. 20 anys del Departament de CAI (1a part)
No full textForum debat: arquitectura i tècnica es celebra el divendres 29 de febrer de 2008 commemorant els 20 anys del Departament de Construccions arquitectòniques (CAI)a la Sala d’actes de l’edifici Vèrtex del campus Nord.Primera part del "Foro Debat: arquitectura i tècnica" amb una presentació del director del Departament de CAI Joan Lluís Zamora Mestre i Josep Lluís González-Barroso i diverses intervencions de convidats
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
- …
