Simulation models of welding processes allow us to predict influence of welding parameters on the temperature field during welding and by means of temperature field and the influence to the weld geometry and microstructure. This article presents a numerical, finite-difference based model of heat transfer during welding of thin sheets. Unfortunately, accuracy of the model depends on many parameters, which cannot be accurately prescribed. In order to solve this problem, we have used simulated annealing optimization method in combination with presented numerical model. This way, we were able to determine uncertain values of heat source parameters, arc efficiency, emissivity and enhanced conductivity. The calibration procedure was made using thermocouple measurements of temperatures during welding for P355GH steel. The obtained results were used as input for simulation run. The results of simulation showed that represented calibration procedure could significantly improve reliability of heat transfer model.

The scope of application of simulation models in welding is limited by the accuracy of their output results. This paper presents a calibration procedure for a three-dimensional quasi-stationary model of heat transfer for gas metal arc welding. The double-ellipsoid heat source used in this model has five input parameters whose value cannot be specified accurately. To estimate these values, we employed a multi-objective calibration procedure with two objective functions using the paretosearch optimization algorithm. Objective functions represented the error between simulated and experimentally observed values of penetration depth and weld bead width during gas metal arc welding of P355GH steel plates. All input parameters were assumed to be a power function of line energy. To reduce computational time, we replaced the numerical model with a response surface methodology metamodel based on an optimal set of simulation results from the numerical model. The results of the simulations based on calculated values of input parameters for the heat source model showed excellent matching with the experimental results.

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Water injection is a means of internal cooling of the engine. During combustion, excess temperatures generated are absorbed by water as latent heat. Optimum water injection quantities were found to be about 0.015 ml to 0.031 ml of water per cycle on a 592 cc SI engine. The experiments were carried out by tapping the fuel injector signal and designing a circuit to inject water at the instant petrol is injected. Fuel injection duration was tuned by using a Wide Band Lambda sensor. The engine was supercharged as well by means of compressed air supply and regulated by hysteresis control. Water injection was investigated while varying spark advance to find the Maximum Brake Torque (MBT). Maximum obtained torque improvement with water injection was 16 %. This was achieved at a manifold absolute pressure of 120 kPa, with air temperature at ambient. The same load condition, 120 kPa, with air heated to the temperature that would be obtained from isentropic compression, resulted in a torque improvement of 7 %.