Numerical Study of a Six-Stroke Gasoline Compression Ignition (6S-GCI) Engine Combustion with Oxygenated Fuels

A numerical investigation of a six-stroke direct injection compression ignition engine operation in a low temperature combustion (LTC) regime is presented. The fuel employed is a gasoline-like oxygenated fuel consisting of 90% isobutanol and 10% diethyl ether (DEE) by volume to match the reactivity of conventional gasoline with octane number 87. The computational simulations of the in-cylinder processes were performed using a high-fidelity multidimensional in-house 3D CFD code (MTU-MRNT) with improved spray-sub models and CHEMKIN library. The combustion chemistry was described using a two-component (isobutanol and DEE) fuel model whose oxidation pathways were given by a reaction mechanism with 177 species and 796 reactions.

The key advantage of six-stroke engine operation is the ability to switch the combustion mode among kinetical controlled mode (KCM), kinetically-driven mixing control mode (K-MCM) and mixing controlled mode (MCM) in the second power stroke (PS2) providing a wider range of combustion control. The K-MCM mode operation has shown to reduce both soot and NOx emissions substantially at low load (around 7bar IMEP) engine operations. The current work focuses on 6S-GCI engine operation using synthetic fuels at high load engine operation with the constraints on pressure rise rate (<10bar/deg), combustion efficiency (>90%), soot and NOx emissions (<1g/kg fuel). With the constraints met, engine operating conditions at 15 bar IMEP and 2000 rpm were identified as a function of fuel split ratio and injection timings. Parametric study was also performed by varying fuel injection pressure, initial gas temperature at IVC, boost pressure and exhaust gas recirculation ratio. Engine performance and emissions characteristics of parametric variation are presented as well.