CFD Simulation and Experimental Validation of a Throttle Body Design without Bypass for Fuel Injected Motorcycles 2015-32-0755
Increased penetration of gasoline EFI (Electronic Fuel Injection) in the Indian two wheeler commuter segment, demands simplified, but robust solutions. Freedom for the end user to adjust the idle speed with carbureted engines is considered as reference behavior. Control of idle air flow in the traditional throttle body designs is through a bypass path with either an idle speed actuator or a mechanical screw. Due to the quality of air and vented blow-by in the air path, field issues observed on most throttle body designs include a) carbon deposition influencing the air flow characteristics b) consequent effects included instability of idle speed, jamming of throttle valve or clogging of idle air control valve. One of the design measures suggested  was to introduce an idle screw on the throttle flap to retain the user experience based on the incumbent carburettor and address the carbon deposition based on the knowledge of ETB (Electronic Throttle Body).
The primary objective of this investigation was to validate this assumption through CFD (Computational Fluid Dynamics) analysis backed by vehicle trials. In CFD, carbon deposition can be characterized as a function of velocity and pressure. This phenomenon was used to simulate air flow in the throttle body with and without bypass path and compared against the experimental results. Further, these configurations were subjected to real world driving conditions to evaluate the effect on carbon deposition phenomenon.
The simulation showed a channeled air flow with the maximum velocity of 353m/s (which is greater than sonic velocity) for throttle body without bypass path. The simulation and experimental results for air mass flow had close agreement with <8% deviation over the entire range of throttle opening. The results from vehicle trials indicated reduced rate of carbon deposition when observed at frequent intervals during the trials. Learning from the iterative steps, vehicle validation results and combination of smart software algorithm enabled a robust throttle body design.