Theoretical studies of natural gas vaporization of an air-methane mixture in a diesel engine cylinder

This article presents theoretical studies of the vaporization of natural gas of an air-methane mixture in a diesel engine cylinder. These studies were conducted in order to find a rational volume of methane supplied to the cylinder of a diesel engine. Having carried out a thermal calculation of the working processes of the gas engine, we obtained the size of the gas droplet supplied to the engine cylinder, which should have a size of no more than 0.405 mm. Having evaluated the experimental studies conducted in this area, the dependence of the nozzle diameter of the nozzle and the diameter of the gas droplet was revealed, it was determined that with a pressure drop on the gas nozzle equal to 0.2 MPa, the diameter of the gas droplet practically coincides with the diameter of the nozzle. Based on this, the diameter of the nozzle of the gas nozzle sprayer is not more than 0.35...0.4 mm. The conclusion of this article is that it is possible to determine the optimal volume of gas supplied and assess the real picture of the processes taking place in the cylinder of a diesel engine only. Keywords: INTERNAL COMBUSTION ENGINE, WORKING FLUID, FUEL, VAPORIZATION, GAS, COMBUSTION

Work Envelope Expansion and Parametric Optimization in WAAM with Relative Density and Surface Aspect as Quality Constraints: The Case of Al5Mg Thin Walls with Active Cooling

The successful and efficient production of parts with specific features by Wire + Arc Additive Manufacturing (WAAM) strongly depends on the selection of proper and typically interrelated deposition parameters. This task might be particularly challenging in the making of thin walls, which might be highly impacted by processing conditions and heat accumulation. In this context, this study aims at expanding the work envelope and optimizing the parametric conditions in WAAM with relative density and surface aspects of the preforms as quality constraints. The experimental approach was based on the deposition of thin Al5Mg walls by the CMT process on its standard welding setup and with an active cooling technique to enhance the deposition robustness. Internal voids were estimated by Archimedes’ method. The surface quality of the walls was assessed through the visual aspect and the surface waviness by cross-section analysis. All the conditions presented relative density higher than 98%. The upgrade of the standard welding hardware to WAAM purposes through the addition of a supplementary shielding gas nozzle to the torch and the intensity of the heat sinking from the part significantly expanded the process work envelope, with its applicability being successfully demonstrated with multi-objective optimization. To sum up, a decision-making procedure is presented towards achieving intended preform quality.

Influence of the CO2 Content in Shielding Gas on the Temperature of the Shielding Gas Nozzle during GMAW Welding

Gas metal arc welding torches are commonly chosen based on their current-carrying capacity. It is known that the current-carrying capacity of welding torches under CO2 is usually higher than under argon dominated shielding gases. In this publication, the extent to which this can be attributed to the shielding gas dependent arc radiation is investigated. For this purpose, the influence of the shielding gas on the thermal load of the shielding gas nozzle of a GMAW torch was calorimetrically measured. These experiments were carried out for four different shielding gases (argon, CO2, and two argon/CO2 mixtures). The measurements were all performed at an average current of 300 A. The welding current was set by adjusting the wire feed rate or the voltage correction. For each case, a separate set of experiments was done. It is shown that the changed arc radiation resulting from the different shielding gases has an influence on the heat input into the gas nozzle, and thus into the torch. For the same shielding gas, this influence largely correlates with the welding voltage.

Innovative Robotic System for MAG Welding with Two Filler Metal Wire Feeders

The article describes an innovative robotic MAG method for the welding for ship elements. The method involves the use of two wire feeders and one torch, making it possible to weld two different steel grades. In addition, the robot application is equipped with an off-line programming DTPS system (Desk Top Programming & Simulation System) as well as an arc sensor, a gas nozzle touch sensor and a laser touch sensor featuring a seam finding function. The system is also provided with a welding parameter monitoring and archiving system.

Numerical Simulation of the Behavior of Hydrogen Source in a Novel Welding Process to Reduce Diffusible Hydrogen

This study aims to reduce the diffusible hydrogen content in deposited metal during gas metal arc welding (GMAW) and flux-cored arc welding (FCAW) which induces cold cracking. To achieve this, a novel welding torch with a dual gas nozzle has been developed. This special welding torch decreases the hydrogen source gas evaporated from a welding wire by the suction from the inner gas nozzle. In order to improve the suction efficiency of this evaporated gas, precise control of the suction gas flow is indispensable. In this paper, a simplified numerical simulation model of this process has been described. This model can take account of the evaporation of the hydrogen source gas from the wire while simulating the behavior of the shielding gas and the arc. Using this model, the effect of suction nozzle structure and torch operating conditions on suction gas flow pattern and suction efficiency was also investigated to understand the process mechanism. Furthermore, the diffusible hydrogen content in deposited metal was measured by chromatography as a validation step. Results show that some of the shielding gas introduced from a shielding nozzle was drawn inward and also branched into an upward flow that was sucked into the suction nozzle and a downward flow to a base metal. This branching height was defined as the suction limit height, which decisively governed the suction efficiency. As a result, in order to reduce the diffusible hydrogen, it was suggested that the suction limit height should be controlled towards below the wire position, where the evaporation rate of the hydrogen source gas peaks through optimization of the suction nozzle design and the torch operating conditions.

Contamination of Coupling Glass and Performance Evaluation of Protective System in Vacuum Laser Beam Welding

Vacuum laser beam welding enables deeper penetration depth and welding stability than atmospheric pressure laser welding. However, contaminated coupling glass caused by welding fumes in the vacuum space reduces laser transmittance, leading to inconsistent penetration depth. Therefore, a well-designed protective system is indispensable. Before designing the protective system, the contamination phenomenon was quantified and represented by a contamination index, based on the coupling glass transmittance. The contamination index and penetration depth behavior were determined to be inversely proportional. A cylindrical protective system with a shielding gas supply was proposed and tested. The shielding gas jet provides pressure-driven contaminant suppression and gas momentum-driven contaminant dispersion. The influence of the shielding gas flow rate and gas nozzle diameter on the performance of the protective system was evaluated. When the shielding gas flow was 2.0 L/min or higher, the pressure-driven contaminant suppression dominated for all nozzle diameters. When the shielding gas flow was 1.0 L/min or lower, gas momentum-driven contaminant dispersion was observed. A correlation between the gas nozzle diameter and the contamination index was determined. It was confirmed that contamination can be controlled by selecting the proper gas flow rate and supply nozzle diameter.