Development of dual fuel combustion models for direct injected heavy duty diesel engines

Kapitel i bok, 2013

A new model incorporating two combustion modes was developed to simulate dualfuel(DF) combustion engines with different fuel compositions (natural gas/diesel oil andmethanol/dimethyl ether (DME)). The model involved two coupled combustion modes: a"conventional" partially premixed reactor diesel mode and a flame propagation mode.For the flame propagation combustion mode, an expression for the reaction rate wasdeduced based on the equation for the flame speed. Laminar flame speeds for theaspirated fuels were calculated using the PREMIX code within the Chemkin-2 packageby using the chemical mechanisms for the fuel compositions and species moleculartransport properties and were subsequently fitted to polynomial expressions. Theturbulent flame speed was assumed to depend on the laminar speed and characteristics offlow turbulence.CFD partial and full cycle engine simulations were performed for two heavy dutydiesel engines, a Volvo D12C and an IF (Isotta Fraschini), using the 3D CFD KIVA3Vand KIVA4 codes supplemented by similar spray models and semi-detailed combustionand emission formation mechanisms for both fuel compositions. The natural gas fuel wasselected as a four-component mixture of methane (>90%), ethane, propane and n-butane,while diesel oil vapor was represented as a blend of n-heptane and toluene. The solutionalgorithm accounted for the two coupled combustion modes by employing aninterpolation procedure. The predicted DF engine in-cylinder parameters (pressure,energy release rate, NOx and H2O/CO2 concentrations) and combustion efficiencies forhe different DF compositions were compared with conventional diesel data for bothengines.