Study On Functional Performance Of Stirling Engine With Simulation And Optimization Models

Worldwide attempts are being made to reduce pollution and alleviate energy scarcity.Recent interest in renewable energy utilization has sparked new activities in Stirling engine development.Stirling engine has become preferable for high attention towards the use of alternate renewable energy resources like biomass and solar energy.However,only few mature Stirling engines have emerged up to the time.Stirling engine is an externally heating engine,which theoretical efficiency is as high as Carnot cycle's,but actual ones are always far below compared with the Carnot efficiency.The real performance of Stirling engine always deviates from prescribed theoretical potential.This is mainly because of complex interaction of different engine parameters,heat transfer process of oscillating flows and fluid dynamics.This thesis presents a detailed study about the functional performance and thermodynamics of Stirling engine with simulation and optimization models.A number of studies have been done on modeling techniques to improve the Stirling system design.In first phase of the study,a concept of multi-objective optimization method,which is a combination of multiple optimization algorithms including differential evolution,genetic algorithm and adaptive simulated annealing,was proposed.This method is an attempt to generalize and improve the robustness and diversity with above three kinds of population based meta-heuristic optimization techniques.The analogous interpreter was linked and interchanged to find the best global optimal solution for Stirling engine design optimization.It decreases the chance of convergence at a local minimum by powering from the fact that these three algorithms run parallel and members from each population and technique are swapped.The optimization considers five decision variables,including engine frequency,mean effective pressure,temperature of heating source,number of wires in regenerator matrix,and the wire diameter of regenerator,as multiple objectives.The Pareto optimal frontier was obtained and a final optimal solution was selected by using various multi-criteria decision making methods including techniques for Order of Preference by Similarity to Ideal Solution and Simple Additive Weighting.The multi-objective optimization indicated a way for GPU-3 Stirling engine to obtain an output power of more than 3kW and an increase by 5%in thermal efficiency with significant decrease in power loss due to flow resistance.Second phase of the study covers the detailed analysis of 100 W beta-type Stirling engine,built by State Key laboratory of Clean Energy Utilization.In order to develop an effective methodology to optimize geometric design of Stirling engines,this beta-type rhombic drive Stirling engine was investigated whose initial experimental efficiency and output power was relatively low.This part presents a sensitivity analysis of ?-type Stirling model with a combined method to carry out multi-objective optimization of a Stirling engine using detailed information of pressure and volume provided by CFD analysis and experimental results.The geometric parameters of heat exchangers including heater and cooler tubes diameter with length,regenerator length,matrix mesh and wire diameter were considered for maximizing thermal efficiency,output power and minimizing flow resistance power loss in Stirling engine.CFD analysis covers a detailed study of real and optimized model with best experimental agreement.The CFD results include the detailed description of Stirling cycle with temperature contour,velocity vectors and pressure-volume variation in compression and expansion spaces.The proposed modification results an increase of 2%in thermal efficiency and more than 80W in power output when the dead volume of heater,cooler and regenerator is reduced up to 54%,42%and 24%respectively.The additional dead volume leads to a phase shift of the pressure,which is also the main reason of lowering output results.The complete study demonstrated Stirling engine design concept with parallel integration of multi-objective optimization algorithms with developed simple analytical model for efficient designing and surveying the performance.Furthermore,the CFD analysis enables in depth investigation of heat transfer,temperature and pressure distribution throughout the engine working cycle.