| The Stirling engine is an external combustion engine, with high thermal efficiency, cleaner discharge, less noise and vibration and better energy adaptability, which is widely used in the civil and military field. In this paper, high-speed photography, thermocouple and exhaust gas analyzer were used to study the combustion and emission characteristics of the Stirling engine using ethanol and diesel as fuel. The main contents include:(1)Experimental study of the combustion flame characteristics1. An oxygen circuit is added to the experimental system of Stirling engine, by means of high-speed photography, The effects of different oxygen concentrations in the ejected air and different air-fuel ratio on flame stability, flame length, flame RGB features, flame spread rate and flame cone angle were investigated, results showed that: ①The flame became more stable, the flame length was shorter, the flame brightness increased, the flame spread rate rose, while the cone angle and the combustion mode of the flame tend to be unchanged, with the increase of the concentration of oxygen in the ejected air; ②As a whole trend, increasing the air/fuel ratio promoted the flame to be more stable, shorten the flame length, rose the flame cone angle and decreased the flame brightness; ③As air/fuel ratio rose, the changes of flame characteristics were slight under the condition of excess air coefficient φa<1 or φa>1; whereas the changes of flame characteristics are obvious when excess air coefficient φa≈1.(2)Measurement of the combustion temperature in the combustion chamberThe study also measured the temperature distribution in the central section of the combustion chamber by means of high-precision high-temperature thermocouple, and analyzed the influence of the concentration of oxygen in the ejected air and different air-fuel ratio on the axial, radial temperature distribution, and the temperature distribution of the central section of the combustion chamber, results showed that: ①With the improvement of the oxygen concentration in the ejected air, the temperature of combustion chamber increased, high temperature area were mostly around the pressure swirl nozzle, the range of high temperature reduced, both axial and radial temperature gradient near the center of chamber increased, and they changed a little in the area next to the top and border of combustion chamber; ②With the improvement of excess air coefficient, the temperature of combustion chamber decreased, the range of high temperature area which are mostly near the nozzle increased, both axial and radial temperature gradient which are near the center of chamber decreased, and they increased in the area next to the chamber wall.(3)Experimental study of the emission performanceThe effects of different amount of ejecting air, oxygen concentration in ejecting air and excess air coefficient on the emission performance of the Stirling engine were also explored, results showed that: ①With adequate air in the combustion chamber, the output of CO increased and the output of NOX increased at first and then reduced; with suitable amount of ejecting air, the output of HC decreased when increasing the air mass flow rate; however, the output of HC increased when excess amount of air is ejected; ②With the increment of oxygen concentration in ejected air, the emissions of CO and HC decreased, while the NOX increased; ③ When the excess air coefficient increases from φa<1 to φa>1, the emissions of CO and HC decreased initially and then increased, the output of NOX decreased all the way.This paper studied both combustion and emission performances of Stirling engine under open and closed environment. The result lays a solid experimental foundation for the performance optimization of Stirling engine. |
PDF Full Text Request