A reduced chemical
kinetic mechanism consisting of 141 species
and 709 reactions has been constructed to simulate the combustion
of both natural gas and diesel fuels in a dual-fuel engine. Natural
gas is modeled as a mixture of methane, ethane, and propane, while
the diesel fuel is modeled as n-heptane. The new
reduced mechanism combines reduced versions of a detailed n-heptane mechanism and a detailed methane through n-pentane mechanism, each of which was reduced using a direct
relation graph method. The reduced dual-fuel mechanism is validated
against ignition delay computations with full detailed mechanisms,
adiabatic homogeneous charge compression ignition simulations with
full detailed mechanisms, experimental premixed laminar flame speeds
of CH4/O2/He mixtures at 40 and 60 atm, ignition
delay and lift-off length from a diesel spray experiment in a constant-volume
chamber, and finally against dual-fuel engine experiments using multidimensional
computational fluid dynamics simulations. The engine simulations were
performed for direct comparison against natural gas/diesel dual-fuel
engine experiments at varying injection timings, engine loads, substitution
percentages, and natural gas compositions. An engine experiment with
additional propane was used to induce engine knock for the purpose
of validating the reduced mechanism’s ability to predict natural
gas autoignition. The results show that the newly reduced mechanism
accurately reproduces the chemical kinetic behavior of the detailed
mechanism, including the laminar flame speed at high pressure, the
ignition delay and lift-off length in the diesel spray experiment,
and the pressure and heat release rate in the engine experiments.
In the experiment where engine knock occurred, the model predicts
the phasing and magnitude of a sudden acceleration in the combustion
rate and reproduces the observed high-frequency pressure oscillations.
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