Improved Modeling and Experimental Evaluation of a Micro Gas Turbine for Solar-Hybrid Application

This study contributes to the ongoing research to develop a turbocharger based dual-shaft Micro Gas Turbine (MGT) for a commercialized solar-hybrid system. The work in this study developed an improved model to predict the performance of the MGT which comprises of two turbochargers, with one turbocharger representing the gas generator turbine and the other, bigger turbocharger used as the power turbine unit. It did so by including the effects of heat transfer through a One-Dimensional Thermal Resistance Network (1-D TRN) to determine diabatic outlet temperatures and by accounting for the supposed incomplete combustion. Overall, the model’s temperature estimations were found to be within a maximum deviation of 5 % of the measured values and, 8 % for pressure. Combustor outlet temperature estimates were substantially improved to within 4 % of the measured value, which is a 15 % improvement on previous work. Despite the increased accuracy, the model was only validated for the smaller gas generator turbine. The larger power turbine was reasoned to have not reached thermal equilibrium as temperature estimates had substantially increased levels of deviation from the measured values. A subsequent energy audit of the facility demonstrated the utility of the 1-D TRN. The results of which were used to determine the scale of the heat transfer. It showed that the power turbine is in fact operating outside of its optimal range which resulted in the heat loss rate of the gas through the turbine being greater than the power it produced. The usefulness of the combustion model is also highlighted as a technique to estimate the combustor outlet temperature with acceptable levels of accuracy and with a rapid turn-around time due to its simplicity. The 1-D TRN was shown to estimate heat flows in the MGT accurately despite employing correlations for the heat transfer coefficients that were not developed for the machines. A combustor designed for solarized operation was benchmarked against a standard unit and the results indicated the significance of reducing parasitic pressure losses as a means to improve MGT performance.