Estimating the behavior of particles sprayed by a single-cathode plasma torch based on a nonlinear autoregressive exogenous model

The thermodynamic properties, transport coefficients and characteristics (i.e., velocity and temperature fields, etc.) of a thermal plasma jet derive from complex non-linear relationships between operating parameters plasma gas mixture, arc chamber design, arc current intensity, etc.). To simulate the operating behavior of such a device, an emulator (input parameters were varied for a given target) can be designed and implemented based on a NLARX (nonlinear autoregressive with exogenous inputs) model. Indeed, simulating the behavior of an atmospheric mono-cathode plasma spray torch used in the APS process requires a global approach which considers those interrelated nonlinear relationships together with those related to the coating structural characteristics, its properties in-service and the operating process parameters (e.g., power, feedstock injection and kinematics). In this work, a system identification methodology allows describing the system behavior based on input-output temporal functions. It has been implemented to process experimental data which were collected versus time, and thus an emulator adapted to this process has been implemented. The emulator included three sub-systems: input, simulator and output. Arc current intensity, hydrogen ratio in the plasma forming gas mixture and the total mass flow rate of the plasma forming gas mixture were considered as input parameters. The average temperature of in-flight particles and their velocity were chosen as output parameters. With experimental data training, the emulator was able to identify relationships depicting the plasma spray torch working conditions. Then the emulator was tested and compared with experimental data. The result showed an average error of about are 1 +/- 0.73% in particle temperature and 2 +/- 1.71% in particle velocity. With this emulator, a new methodology to study the plasma spray process is proposed, in particular to control the thermal spray process more precisely. (C) 2014 Elsevier B.V. All rights reserved.