350-360Throttle body assembly plays a vital role in
metering the airflow. It mainly consists of a butterfly valve to vary the flow
area to control air flow rate through it. There is hardy any established
procedure to design a throttle body assembly based on the engine
specifications. In order to bridge the gap, this study, design and optimization
of a throttle body assembly for a single-cylinder engine used in two-wheeler
application has been analyzed along with the investigation of critical flow
through various sub systems using computational fluid dynamics (CFD). To start
with, the throttle bore and bypass passage diameters are calculated from the
basic flow equations. Using CFD, best possible throttle shaft profile is
arrived at, which will enhance airflow to the engine. The airflow rate for
different throttle openings is predicted taking into account the distribution
of main and bypass flow. It is observed that the airflow through main and the
bypass passage are almost same around 12% throttle opening and the airflow
through main passage takes over beyond 25% opening. The novelty of this study
is that airflow through the bypass is also predicted for different screw
positions. From the analysis of results, it is found that with around two turns
of bypass screw opening, the required amount of air flow rate could be achieved
through the bypass passage to run the accessories of the engine at idling and
also to meet the required performance and emissions levels as per the design
target. In addition, there is a good agreement of CFD predictions with
experimental results with an error of about 6%. Finally, it is concluded that
the procedure adopted in this study to design the throttle body as per engine
specifications will be very useful for the engine designers and in this aspect,
CFD plays an important role