In this paper, comprehensive governing differential equations of Stirling engines have been developed by coupling the effect of gas leakage through the displacer gap, gas leakage into the crank case and the shuttle loss rate into the traditional model. Instantaneous pressures and temperatures of the working fluid in the engine were evaluated at same time step.The present model was deployed for the thermal simulation of the GPU-3 Stirling engine and the obtained results were robustly compared to experimental data as well as results from previous numerical models. Then, parametric studies were conducted to assess the impact of geometrical and operating parameters on the performance of Stirling engines working with helium or hydrogen. Results suggest that the modifications made in this model led to better accuracy and consistency in predicting the experimental data of the prototype engine at all speeds, compared with most previous models. It was found that there exists a minimum dimensionless gap number, for every engine pressure below which mass leakage into the compression volume may not impact the brake power and energetic efficiency of the engine.In addition, an optimum mean effective pressure was found for maximum energetic efficiency of the engine. This optimum value is higher for helium gas than for hydrogen gas. Further results indicated that the brake power and energetic efficiency of the prototype Stirling engine can be significantly improved by 30% and 18%, respectively, provided that the heater temperature is raised to 850 ℃ while the cooler temperature is reduced to 0 ℃.

This study compares the performance of a thermal power plant fired by natural gas to that fired by biodiesel blend, from exergetic and economic perspectives. A thermodynamic model has been developed to predict the performance of a running plant and was used to conduct the comparative study. Plant life of 25 years has been used to assess the viability of the gas turbine power plant by analyzing the net present cost and the break-even point for both fuels. The plant specific fuel consumption for natural gas fired and biodiesel blend fired are 0.3151[kg/kWh] and 0.3884 [kg/kWh] respectively. The system fired by natural gas only, has a payback period of 1.9 years, internal rate of return of 52% and exhaust temperature of 915.74 [K], while that fired by the biodiesel blend has a payback period of 2.4 years, internal rate of return of 60% and exhaust temperature of 858.50 [K]. Nevertheless, biodiesel blend is preferable because it is biodegradable, produces less emissions, and as a consequence, environmentally benign. Biodiesel blend would be more suitable for firing gas turbine engines, if the combustor is redesigned to improve its efficiency. Thermo-economic analysis of gas turbine power plants is essential to improve its thermodynamic and economic performance.

No abstract