Characteristic of Response of Carburetted SI Engine under Transient Conditions

An experimental study was made of the transient characteristics of fuel flow pattern in a carburetor and an intake manifold as well as their effects on the engine performance of a carburetted four cylinder SI engine under transient driving conditions. The results show that the beginning of fuel discharge from the main nozzle of carburetor is delayed by an increase in opening rate of throttle valve. The velocity of liquid fuel film on the wall of intake manifold is expressed as a function of the opening rate of throttle valve θ^., showing a maximum value at a certain rate θ^.. The formation of lean mixture is affected much more intensely by the flow delay of liquid fuel film in the intake manifold than by the delay in fuel discharge from the carburetor and this can be avoided by heating the liquid fuel before its supply into the manifold.