Abstract
In a premixed dual-fuel (DF) methane-diesel engine, the ignition of the
lean premixed methane/air mixture starts with the assistance of a pilot
diesel injection. Auto-ignition of pilot fuel is important as it
triggers the subsequent combustion processes. A delay in the
auto-ignition process may lead to misfiring, incomplete combustion, and
thus higher greenhouse emissions due to methane slip. Hence, a better
understanding of the auto-ignition process for the pilot fuel can help
to improve the overall engine performance, combustion efficiency, and to
lower exhaust emission levels. In the present study, large eddy
simulation (LES) is used to investigate the auto-ignition process of
micro-pilot diesel in premixed DF combustion in a constant volume
combustion chamber (CVCC). The entire DF combustion processes including
methane gas injection, methane/air mixing, pilot diesel injection, and
ignition are simulated. The numerical model is validated against
experimental data. The present numerical model is able to capture the
ignition delay time (IDT) within a maximum relative difference of 7% to
the measurements. A higher relative difference of 38% is obtained when
methane gas injection and mixing are omitted in the simulation and the
methane/air is assumed homogeneous. This demonstrates the importance of
inhomogeneity pockets. To study the effects of temperature and methane
inhomogeneities separately, different idealized inhomogeneities in
temperature and methane distribution are considered inside the CVCC. The
inhomogeneity in the temperature is observed to have a more profound
influence on the IDT than the methane inhomogeneity. The inhomogeneity
pockets of temperature advance the first-stage ignition and,
subsequently, the second-stage ignition. A sensitivity analysis on the
effect of inhomogeneity wavelength reveals that the larger wavelengths
enhance the combustion due to the presence of pilot diesel jets in the
desirable regions for a longer time duration.
Original language | English |
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Article number | 128593 |
Journal | Fuel |
Volume | 349 |
Number of pages | 10 |
ISSN | 0016-2361 |
DOIs | |
Publication status | Published - 2023 |
Keywords
- CFD simulation
- Dual-fuel combustion
- Inhomogeneity
- LES
- Micro-pilot diesel ignition
- Premixed methane