Arc welding is usually used for bonding structural members and machine parts. When some defects or cracks are detected, however, it sometimes provides practical and effective means for compensating the strength of welded joint as a so-called repair welding. In normal practice, the regions containing defects are removed as a circular hole whose diameter is larger than 8cm. A circular plate with the same diameter is placed to plug the hole; then the repair welding with curved beads is conducted to bring the structure into the original shape. In this paper, a numerical approach using three-dimensional Finite Difference Method (FDM) in the transient temperature field is presented for evaluating the fundamental characteristics of cooling process of patch welding with curved beads. Arc welding is performed to verify the validity of the proposed numerical method by measuring the cooling process at the welding junction. In addition, the numerical results of temperature distributions on plate surface are also compared with those obtained by infrared thermography.
A great deal of attention has been focused on decreasing the piston assembly friction in piston engines, since this friction acounts for the majority of total mechanical power loss in these type of engines. The tribology of the sliding surfaces between piston rings and cylinder liner includes extremely complicated phenomena which will become even more severe with an increase in the engine power. In the present study, the theoretical analysis on the mixed lubrication of piston rings is made. The analysis is comprised of Patir and Cheng's average flow model and Greenwood and Tripp's asperity interaction model, and is developed to consider the shear thinning effect of non-Newtonian fluid, multigrade oil. The friction characteristics of piston rings for both monograde and multigrade oils are investigated and compared with experimental results obtained by the floating liner method, which can measure the instantaneous friction force of a piston assembly under firing conditions.
In this study, experiments were carried out to investigate the effects of fuel properties such as cetane number, aromatic content on NO, THC, smoke and particulate emissions of a DI diesel engine. Cetane number and aromatic content of the fuels were varied independently to separate their effects on emissions. The results showed that for the fuels with the same aromatic content, reducing cetane number resulted in the decrease of particulate emission and the increase of NO emission. As cetane number was kept constant, changing the aromatic content had little effect on combustion characteristics. However, increasing aromatic content resulted in higher particulate and NO emissions. At retarded injection timing, for the low cetane number fuels, THC increased dramatically at low load due to the overleaning caused by long ignition delay. In particular, for the low cetane number fuel with aromatic content, not only THC but also SOF increased at low load. As the injection pressure was raised, NO increased and particulate decreased for all fuels tested, and also particulate emission became less sensitive to fuel properties.
We have always suplied diesel engines and around systems that are in harmony with times request. 22HLX·28HLX·34HLX type diesel engines are newest diesel engine and planned as our company'snext generation “new medium speed engine” based on achievements of existing Niigata medium speed diesel engines. 22HLX series come with 6·8 and 12·16·18 cylinders, 28HLX series also with 6·8 and 12·16·18 cylinders, and 34HLX series comes with 12·16·18 cylinders. HLX series cover a wide range of output that is from 1392kWm to 9990kWm. The following will introduce the “new medium speed engine” 28HLX.
This paper describes the influences of fluctuation factors in respect to NOx emissions from medium speed generating diesel engines. In order to confirm the possible influences of absolute humidity Ha, air temperature Ta and intercooled air temperature Tsc, in an attempt to correct the measured result of NOx, annual NOx data was modified through two cogeneration engines of 220mm and 280mm in bore. The result indicates that the influence degree from the absolute humidity factor is larger than from the other factors. It was found that annual NOx variations could not be eliminated by the correction formula as given by the Technical Code.
This paper describes the results of the combustion test by controlling the absolute humidity and the cylinder inlet air temperature in air in order to confirm the NOx variations in the medium speed single cylinder diesel engine with 200mm in bore. The absolute humidity is controlled by varying the quantity of water injected into the suction port. These findings show a close proximity to the result of research conducted by the authors on “Follow-up Survey on NOx Concentration from Cogeneration Engines”