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176 TRƯỜNG ĐẠI HỌC SƯ PHẠM KỸ THUẬT - ĐẠI HỌC ĐÀ NẴNG

a lean mixture, hydrogen allows for the expansion of element volumes did not become excessively small,
the flammability limit, improving both economic and leading to program termination, the cylinder region
technical performance and reducing NOx emissions as was meshed with larger elements compared to the
hydrogen content increases [18-20]. other regions.
The presence of hydrogen in a mixture with The computational domain was divided into three
biogas not only reduces pollutant emissions from zones: cylinder, combustion chamber, and intake port.
spark-ignition engines but also contributes to reducing Each zone had a different mesh size, as illustrated in
soot emissions in dual-fuel biogas-diesel engine Figure 1.
exhaust [21-22]. Wang et al. [23] proposed that a To enable the engine to operate on variable
hydrogen volume content of about 20% in a mixture biogas-hydrogen blends, the original carburetor and
with methane is optimal for both thermal efficiency ignition system were replaced with an electronic fuel
and pollutant emission levels. The ignition timing injection system and electronically controlled
significantly affects the performance quality of biogas ignition. The study focused on the mixture formation
engines enriched with hydrogen [24]. In general, and combustion processes, hence the computational
hydrogen can be considered an additive to biogas to domain included the intake port, cylinder, and
improve performance and reduce pollutant emissions combustion chamber. The geometry of these domains
due to its superior properties such as extended was designed in GAMBIT. The mesh generation was
flammability limits, high combustion speed, large performed automatically. Due to the varying cylinder
diffusion coefficient, and high adiabatic temperature volume during piston movement, the elements within
[25]. Enriching biogas with hydrogen clearly the cylinder were deformed. To ensure that the
improves the engine's combustion process. However, element volumes did not become excessively small,
the downside is that it increases NO x emissions, leading to program termination, the cylinder region
causing environmental pollution. NO x depends on the was meshed with larger elements compared to the
temperature distribution and fuel/air mixture other regions. The computational domain was divided
composition in the combustion chamber. Therefore, into three zones: cylinder, combustion chamber, and
thoroughly studying the mixture formation process intake port. Each zone had a different mesh size, as
when the engine runs on hydrogen-enriched biogas is illustrated in Figure 1.
essential to maximize the efficiency of using
renewable fuels. In this study, the injection time
provided by simulation and experimentation of an
engine using biogas-hydrogen fuel will be compared.
Based on this, an electronic controller will be
proposed to control the injection time of an engine
running on biogas-hydrogen fuel with flexible
component variations.
2. SIMULATION STUDY
The simulation was conducted on a Honda GX200
forced-ignition engine with a cylinder bore D =
68 mm, piston stroke S = 45 mm, and a compression
ratio of 8.5. When operating on gasoline, the engine
produces a power output of 4.8 kW at 3600 rpm. The
original engine was fueled by a carburetor and ignited Fig. 1. Meshing the computational space
by a magneto with a fixed advance angle. The computational simulation was carried out
To enable the engine to operate on variable using Ansys Fluent 2021R1. The convection-diffusion
biogas-hydrogen blends, the carburetor and original equations were solved using the k-ε turbulence model.
ignition system were replaced with an electronic fuel The thermodynamic properties of the mixture were
injection system and electronically controlled determined using the Partially Premixed model. When
ignition. The study focused on the mixture formation changing the fuel type, the pdf tables of
and combustion processes, hence the computational thermodynamic properties were updated to simplify
domain included the intake port, cylinder, and the boundary conditions. The intake port inlet
combustion chamber. The geometry of these domains contained only air, thus the mixture fraction f
was designed in GAMBIT. The mesh generation was (volumetric fraction) was 0, while at the injector
performed automatically. Due to the varying cylinder inlets, only fuel was present, so f = 1. The local
volume during piston movement, the elements within equivalence ratio of the mixture was calculated based
the cylinder were deformed. To ensure that the on the fuel composition, oxygen, or the value of f.
ISBN: 978-604-80-9779-0