(6dx) Three-Dimensional Numerical Simulation of Natural Gas/Methanol Dual-Fuel Engine

Research Interests: Three-dimensional
Numerical Simulation of Internal Combustion Engines

Teaching Interests: Power
Engineering and Engineering Thermophysics

Three-dimensional Numerical Simulation of Natural
Gas/Methanol Dual-fuel Engine

Q Zhang, Z Chen

Institute of the Internal Combustion Engine, Xi¡¯an Jiaotong University, Xi¡¯an, Shaanxi 710049, China

Three-dimensional numerical
simulation of natural gas/methanol dual-fuel engine

                                                 Q
Zhang, Z Chen

Natural gas is widely used as
an alternative fuel for internal combustion engines because of its clean
combustion characteristics and abundant reserves. However, under lean-burn and
light load conditions, relatively low laminar flame speed of natural gas also
causes poor emission. Natural gas/methanol dual-fuel combustion mode can well
solve those shortcomings since methanol has higher laminar flame speed and
higher oxygen content. A large amount of experimental data showed that natural
gas combustion process was accelerated and engine performance was improved with
methanol enrichment. But the underlying reason is unclear. 3D simulation is
commonly used to visualize the process of combustion in an engine cylinder.
Lots of simulation models are used to study the performance of natural gas
engines while models used to study methanol/methane dual-fuel engines are still
limited.

In this work, firstly, we use
the software Pro/E to create a complete three-dimensional model contains intake
port, exhaust port, intake valves, exhaust valves, and cylinder. Then importing
the model into the CONVERGE simulation software to automatically generate
calculation grids. After that, the detailed methanol/methane combustion
reaction mechanism of Galway University was simplified, and the accuracy and
reliability of the simplified reaction mechanism was verified. By using this
complete model, simulation was first started with the intake and exhaust
process to obtain the whirl ratio, the turbulent kinetic energy, and the
turbulent energy dissipation rate in cylinder at the time of intake valves
close. Second, we create a 1/6 model of the cylinder to simulate the combustion
process. Compared with complete model, 1/6 model could help to save a lot of
time needed for computation. Meanwhile, the three-dimensional model was
calibrated by using cylinder pressure data obtained from engine experiment.

Simulation results show that
the addition of methanol increases the maximum of in-cylinder pressure and
advances combustion phase. Apart from that, with the increasing of methanol
substitution rate, unburned hydrocarbon emissions decrease while the emissions
of nitrogen oxides increase slightly. These simulation results are consistent
with experimental results. Through the analysis of those simulation results, it
could be concluded that higher laminar flame speed of methanol accelerates the
combustion of natural gas engine and makes the combustion more efficient.