Experimental demonstration of dark current mitigation by an
over-inserted plug in a normal conducting VHF gun
Xueyuan WangGuoxiang ShuHao QianX. LiZhi LiuZhiyu JiangHaibo MengChaozhu XingQuanlai ZhouHaixiao Deng
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Abstract:
The room temperature continuous wave (CW) very-high-frequency (VHF) gun is one of the candidates for the electron gun of the high-repetition-rate free-electron lasers (FELs). The VHF gun operates with a cathode gradient of ~ 20 MV/m and an accelerating voltage of ~ 750 kV. The gun dark current emission leads to beam loss along the FEL machine, therefore is a critical parameter for the performance of the CW gun. In this paper, we presents a systematic study of the dark current reduction of the VHF gun, including cathode region optimizations, dark current tracking simulations and measurements. Over-inserted cathode plugs were tested in two VHF guns of different acceleration gap sizes, and both demonstrated significant dark current reduction ratios of more than two orders of magnitude.Keywords:
Spark plug
New concept spark plug was developed to study its influence on the combustion characteristics of SI engine. It has pre-ignition chamber at the lower end of spark plug and flame hole, in which fresh mixture gas can be put in through the flame hole without any fuel supply system. This spark plug was tested in a single cylinder engine dynamometer for different air fuel ratio to measure the fuel consumption rate, emission gases, and MET timing. And constant volume combustion chamber was made to understand flame characteristics of spark plug. New spark plug induced fast burn compared to the conventional spark plug and its effects were increased in lean air fuel ratio. Pre-ignition chamber spark plug with 5 holes which had adjusted size was more stable and effective in combustion performance than pre-ignition chamber spark plug with 1 hole. And its effects showed larger differences in lean air fuel ratio than stoichiometric condition. Flame kernel and flame growth process of conventional spark plug and pre-ignition chamber spark plug studied by flame visualization of schlieren method.
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Engine knocking
Lean burn
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The spark plug with integrated chamber increases the quality of ignition of the homogeneous mixture in the engine cylinder.The discharge of a very small amount of a burning mixture from the chamber (the so-called chamber ignition) leads to a faster development of the initial burning phase, and the subsequent burning of the mixture in the cylinder is then more stable in terms of inter-cycle variability.However, the spark plug housing with the integrated chamber is exposed to a higher thermal load compared to a conventional spark plug, and this must therefore be respected when constructing a spark plug with an integrated chamber.The paper shows the impact of the design of the spark plug with the integrated chamber on the temperature at the bottom of the cellular spark plug housing.
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The new concept spark plug was developed to study its influence on the combustion characteristics of SI engine. It has pre-ignition chamber in the lower end of spark plug and flame hole, in which fresh mixture gas can be introduced without any fuel supply system. This spark plug was tested with a commercial SI engine. Fuel consumption rate, emission gas and MBT timing were measured in the engine dynamometer for various flame hole numbers, hole positions, hole sizes of the pre-ignition chamber of the spark plug. And average flame propagation speed was measured by using the head gasket ionization probe in single cylinder engine. The new concept spark plug induces fast burn in combustion compared with the conventional spark plug, and MBT(Minimum advance for Best Torque) timing was retarded about 3~5˚ crank angle. The flame hole number, hole direction and volume of pre-ignition chamber were found to influence the combustion characteristics.
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Engine knocking
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This paper describes some results of the research in the area of multiple spark ignition engines In the single spark plug engine there is a high exhaust emission and low break thermal efficiency because of incomplete combustion .To overcome this problem new dual spark plug engine is developed. Dual spark ignition system has proved their potential in improving the performance of the engines and improved emissive characteristics as compared with the single spark plug ignition system. Recently a new type engine has been introduced which uses triple spark plugs at different location, controlled by an advanced electronic control unit. This advanced electronic control unit uses three different ignition timings with variable spark plug number. Experiments were conducted at different load conditions and different types of engines has proved that dual spark plug ignition engines are surely better than a single spark plug engine, but triple spark ignition engines has proved their potential .It is experimentally investigated that in the single spark plug mode the centrally located spark plug is most effective and gives best performance. In the dual, triple and four spark plug mode if the central location of the spark plug is not possible because of the design of the engine than spark plugs were considered to be located diametrically opposite to each other on cylinder head axis symmetrically. According to Dimensionless distance from the cylinder centre to spark plug location on cylinder head, rsd = rs/R, five locations (rsd = 0, 0.25, 0.50, 0.75, and 1.0) were considered. Inevitably rsd = 0 corresponds to the single spark arrangement that the plug is located at the centre. To comparison, single-spark plug configurations were also considered for other selected spark plug locations. Current paper investigates the effect of multi spark plug to the single spark plug on the basis of the performance of engine and emissive characteristics of engine. The result shown that the considerable improvement in the performance of engine output and considerable reduction in BSFC,HC and Co emission in multi spark plug mode.
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Abstract Robust engine operation with long maintenance intervals and low emissions is the key to meeting future engine requirements. At the same time, engines should be environmentally friendly, resource-friendly, and cost-effective to produce and operate. To meet these market requirements, a central component in engine development is the ignition system and in particular the spark plug. To increase the maintenance intervals of internal combustion engines, it is necessary to increase spark plug lifetime by reducing spark plug wear. The electrode materials used to date are often expensive and rare, and their mining is not without controversy. Successful use of alternative spark plug electrode materials which are available in large quantities, inexpensive, and more resistant to wear than existing materials with similar ignition behavior would advance engine development so it can meet further economic and environmental requirements. To this end, ceramic spark plug electrodes were investigated to determine their spark and ignition behavior as well as their wear. These materials seem to be an interesting alternative to existing spark plug electrode materials. This paper presents a spark plug with ceramic spark plug electrodes that achieves conditions similar to those of standard spark plugs in terms of secondary voltage trace and ignition behavior. Furthermore, it introduces a sophisticated method for scientific, cost-effective, and application-oriented development. Finally, it provides a promising outlook for the ignition behavior and combustion performance of engines with this spark plug.
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Spark plug
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New concept spark plug was developed to study its influence on the combustion characteristics of SI engine. It has pre-ignition chamber in the lower end of spark plug and flame hole. Fresh mixture gas can be got in pre-ignition chamber of spark plug without any fuel supply system. This spark plug was tested to a commercial engine. Fuel consumption rate, emission gas and MBT timing were measured in the engine dynamometer varying the flame hole number, hole position, hole size of the pre-ignition chamber of the spark plug. New concept spark plug induces fast burn in combustion than comparing with the conventional spark plug. MBT timing was retarded about 3~5˚ crank angle. The flame hole number, hole direction and volume of pre-ignition chamber were found to influence emission gases.
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Ignition timing
Engine knocking
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This study presents development of a new pump by modifying existing automotive spark plug, which is generally used for providing an electrode gap to produce an ignition in fuel-air mixture. Compressed air trapped between upper piston surface and spark plug was utilized by modifying spark plug design by implementing Pugh’s method. Keyword: Automotive spark plug, Pugh’s method
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Automotive engine
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New concept spark plug was developed to study its influence on the combustion characteristics of SI engine. It has pre-ignition chamber at the lower end of spark plug and flame hole, in which fresh mixture gas can be put in through the flame hole without any fuel supply system. This spark plug was tested in a single cylinder engine dynamometer for different air fuel ratio to measure the fuel consumption rate, emission gases, and MBT timing. And constant volume combustion chamber was made to understand flame characteristics of spark plug. New spark plug induced fast burn compared to the conventional spark plug and its effects were increased in lean air fuel ratio. Pre-ignition chamber spark plug with 5 holes which had adjusted size was more stable and effective in combustion performance than pre-ignition chamber spark plug with 1 hole. And its effects showed larger differences in lean air fuel ratio than stoichiometric condition. Flame kernel and flame growth process of conventional spark plug and pre-ignition chamber spark plug studied by flame visualization of schlieren method.
Spark plug
Ignition timing
Laser ignition
Engine knocking
Lean burn
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