Numerical Simulation And Analysis On Combustion In CBM Engine

In recent years,due to the shortage of the energy resource,the serious pollution to the living environment,and the frequent CBM explosion accidents,it becomes more and more important for human developing to research that how rationally use clean alternative fuel CBM.The technology of using CBM of higher methane concentration (>30%) has matured, while the CBM in which the methane volume fraction is0%-30%, is most directly emptying. It is one important way to make use of low concentration CBM,as generator fuel.But because huge changes in gas components, it is not an easy work to apply low concentration CBM in engine,so only a small part of that applied to the generator.On this background,this paper studied the combustion characteristics and the engine performance in the8300CBM generator.Based on GT-power, built the engine model and applied Dual-zone quasi-dimensional combustion model SI-Turb and Two-Weibe.Based on this engine model,and according to the characteristics of the fuel,this paper studied the changing rules of the combustion characteristics (flame speed,burn rate,burn radius,heat release rate,cylinder pressure, cylinder temperature) and the engine performance (engine’s power performance and fuel consumption) along with ignition system (advanced angle,spark plug gap),excess air coefficient,gas components in low methane concentration CBM engine.The results show that:1) Under the same operating condition,with the advance of the ignition advance angle,the flame propagation speed,the burn rate,the cylinder pressure and the cylinder temperature is upped;the combustion duration is reduced;the negative work which the piston does is increased;the mechanical efficiency is decreased;the engine’s power performance and fuel consumption are both dropped. With the advance of the ignition advance angle,the emission of NOx increases,but the emission of CO decreases.When the ignition advanced angle is too later,the after combustion period becomes longer,the combustion duration is increased and the fuel is burning in the expansion stroke,the engine’s power performance is dropped quickly.So the engine performance will be deceased in the condition both of the ignition advanced angle is too advance and too later.The simulation results show that the engine performance receives a best value at the work condition of that the ignition advanced angle is25CAD.2) Under the same operating condition,with the increase of the spark plug gap (0.4-0.6mm),the initial flame speed is increased.When the spark plug gap is1mm,the engine’s power performance is the best. 3) At the stoichiometric ratio, the fuel combustion rate is the quickest,the combustion duration is the shortest and the engine’s power performance is the best While the Excess air coefficient is1.25,the fuel consumption of the engine is the best.4) The inert gas in the CBM fuel has strong inhibition effect on the combustion characteristics,especially,the carbon dioxide. With the increases of the inert gas volume fraction, the flame propagation speed is decreased, the combustion duration is lengthened.The simulation results show that the engine’s performance can be improved by changing the engine’s parameters. With the increases of the C2+volume fraction,the flame propagation speed is accelerated,the combustion duration is shorten,the cylinder temperature is lowed.