The research engine used in this work was a Honda Nova Sonic.
It is a single-cylinder, gasoline engine with overhead camshaft.
Bore and stroke are 58 and 47 mm, respectively. The displacement
volume is 125 cm3. The combustion chamber is cylindrical in shape
with the compression ratio of 11:1. The four-stroke, naturally aspirated,
water-cooled, spark ignition engine is a popular motorcycle
engine model in Thailand. Since the biogas is used as a source of
energy in place of gasoline, the engine must be modified to accommodate
the use of biogas [15]. Consequently, the carburetor is replaced
with a gas–air mixer also known as a venturi mixer. Biogas
is supplied through a plastic pipe and mixed with inlet air in the
mixer. Change in airflow quantity and velocity causes a change
in pressure at the channel contraction which in turn affects a
change in flow of biogas to join and mix with the main airflow in
the required proportion, prior to intake into the engine cylinder.