Semi-Empirical Investigation of Engine Speed Effects on Trapping/Scavenging Efficiencies of a Natural Gas Two-Stroke Free Piston Linear Engine Alternator 2019-01-0199
Operating conditions of a 1 kW natural gas two-stroke engine have been investigated to compare the effects of scavenging case pressure as well as variable piston speed on trapping/scavenging efficiencies. A reduced model of the in-cylinder volume from the top dead center (TDC) to bottom dead center (BDC) was generated consisting of intake and exhaust ports. The pressure profile at the intake port obtained from experimental tests was used to consider the crankcase pressure for input into the CFD simulation. Also, at steady state, gas mixture properties from experimental tests at exhaust port open (EPO) crank angle (CA) were extracted and imported as initial conditions into the CFD simulation. This semi-empirical method eliminates the complicated combustion simulation at steady state and significantly reduces the simulation CPU time. An ideal gas model was used along with a dynamic mesh to simulate the gas exchange in a single cylinder two-stroke natural gas engine CFD model. Results showed enhanced trapping and scavenging efficiencies at higher speeds and consequently increased peak in-cylinder pressure. Experimental tests were done in order to validate the CFD results. There is a good agreement between numerical and experimental results with an average error within ±5%.
Nima Zamani Meymian, Derek Johnson, Mahdi Darzi, Nigel Clark, Parviz Famouri