Using ammonia as a carbon-free fuel is a promising way to reduce greenhouse gas
emissions in the maritime sector. Due to the challenging fuel properties, like
high autoignition temperature, high latent heat of vaporization, and low laminar
flame speeds, a dual-fuel combustion process is the most promising way to use
ammonia as a fuel in medium-speed engines.
Currently, many experimental investigations regarding premixed and diffusive
combustion are carried out. A numerical approach has been employed to simulate
the complex dual-fuel combustion process to better understand the influences on
the diffusive combustion of ammonia ignited by a diesel pilot. The simulation
results are validated based on optical investigations conducted in a rapid
compression–expansion machine (RCEM). The present work compares a tabulated
chemistry simulation approach to complex chemistry-based simulations. The
investigations evaluate the accuracy of both modeling approaches and point out
the limitations and weaknesses of the tabulated chemistry approach. When using
two fuels, the tabulated chemistry approach cannot reproduce misfiring events
due to inherent model limitations. By adjusting the model parameters of the
tabulated chemistry model, it is possible to reproduce experimental results
accurately for a specific case. However, using the adjusted parameters for
simulations with changed injection timing or interaction angle between the
sprays shows that no predictive calculations are possible. The parameter set is
only valid for a single operation point.
Further simulations show that the complex chemistry approach can capture the
complex interaction between both directly injected fuels for different operation
points. It correctly predicts the ignition as well as heat release. Therefore,
the approach allows predictive combustion simulations. Furthermore, it
reproduces the occurrence of misfiring in cases of unsuitable interaction of
both sprays and injection timing.
