Manifold Fuel Film Effects in an SI Engine

A test program was conducted with a carbureted 2.3-liter engine in which a map of engine operating conditions over which intake manifold wall films of appreciable magnitude exist was defined on the basis of visual observations. It was found that the largest maldistributions of fuel/air ratio among the four cylinders of the engine occurred during operation at conditions characterized by the presence of extensive fuel puddles on the intake manifold floor. However, it was also found that while the intake manifold fuel films and puddles could essentially be eliminated by heating the manifold floor, the fuel/air ratio distributions among cylinders under such conditions were virtually identical to those measured under conventional operating conditions. On the basis of these data, it was concluded that the steady-state distribution of fuel among the cylinders was not affected by the presence of liquid films or puddles within the intake manifold but rather that the resulting maldistributions were attributable to other charge stratification effects in the intake flow process.