CFD MODELING OF DIESEL OIL AND DME PERFORMANCE IN A TWO-STROKE FREE PISTON ENGINE

This paper presents the CFD KIVA3V, rel. 2 model and numerical results of combustion process simulations in a two-stroke, uniflow scavenging dual free piston engine, FPE, designed for electricity generation. Two fuels, diesel oil and dimethyl ether (DME), were studied in order to achieve HCCI-like combustion. Limited size reaction mechanisms were constructed and used in the modeling. The diesel oil surrogate mechanism consisting of a mixture of n-heptane and toluene includes 70 species participating in 305 reactions, whereas the mechanism for DME consists of 43 species participating in 211 reactions. The combustion development has been simulated in a FPE prototype geometry. It is illustrated that by varying the direct injection timings, a comparably efficient, low-emission operation has been achieved for both fuels. Specific difficulties when using slowly vaporizing diesel oil and rapidly vaporizing DME are outlined.