Design, Fabrication and Evaluation of Gamma-Type Stirling Engine to Produce Electricity from Biomass for the Micro-CHP System

Abstract

Abstract With consideration of the biomass energy potential, a gamma type Stirling engine with 220cc swept volume and 580cc total volume was designed, optimized and manufactured. The engine was tested with helium. Working characteristics of the engine were obtained within the range of heat source temperature 370- 410˚C and charge pressure 10 bar for biomass resources and heat source temperature 540- 560 ˚C and range of charge pressure 1-12 bar with 1 bar increments at each stage for gases. By using of thermodynamic and heat transfer design methods, the key parameters of the designed Stirling engine like required surfaces for heat transfer were calculated (hot side 307 and the cold side 243 squares of centimeters). For analysis of fluid flow, two-dimensional flow analysis method was performed by the software CFD methods. The principles of thermodynamics as well as Schmidt theory were adapted to use for modeling the engine and then pressure - volume diagrams of the thermodynamic and Schmidt analysis were compared. During the test, the temperature is monitored by thermocouples and the pressure of the working fluid helium is monitored by pressure sensors. Indicated power, friction power and brake power were measured and maximum brake power output was obtained with helium at 550˚C heat source temperature and 10 bar charge pressure at 700 rpm as 96.7 W. Electrical energy produced from biomass sources. Sugarcane bagasse, wood, wheat straw, poplar wood and sawdust as fuel system were selected. Most power be obtained from the sawdust (46 watt) and pruning of trees for wood for low power (21 watts), respectively. Minimum ignition time of the Sawdust (4 min) and the most time flammable wood from pruned trees (10 min) was measured. At maximum power, the internal thermal efficiency of the engine was measured as 16%. The test results confirm the fact that Stirling engines driven by temperature of biomass gases are able to achieve a valuable output power. Results of the present work encouraged initiating design of a single cylinder, gamma type Stirling engine of 1 kWe capacity for rural electrification.