Design and optimization of the intake system of a Formula SAE race engine

Several motorsport competitions impose restrictions on intake systems to limit maximum engine power. Since the restriction interferes with the efficiency of the intake system as a whole, it is necessary to study ways to minimize the negative effect of changes in engine performance. In practice, the regulation imposes restrictions to the inlet air which motivates the search for the minimum pressure loss in the restrictor while maintaining an equal volumetric efficiency between the cylinders. This way, it is necessary to tune the duct lengths and diameters, and plenum volume to obtain the maximum volumetric efficiency in the most required speeds. Formula SAE competition imposes an intake system restriction of 20 mm or 19 mm diameter (for gasoline or ethanol fueled engines, respectively). Thus, to reduce pressure loss in the imposed restriction orifice, a system with a convergent divergent duct forming a venturi tube was used. This venturi was designed to maximize its discharge coefficient to increase engine volumetric efficiency. Considering that the focus of motorsport competitions is performance, this paper presents a method to minimize intake system restriction which interfere on engine performance. GT-Suite software was used to create an engine thermodynamic model, with focus on the optimization tool for DoE (Design os Experiment). The results of this study showed a considerable increase on the volumetric efficiency between 6000 rpm and 10000 rpm for the proposed four cylinder 0.6 liter engine. Consequently, increase on torque and power were also obtained. Thus, the maximum torque developed in chassis dynamometer reached 5.8kgfm and the maximum power in 76HP, which represents an increase of 1.8% on torque and 22.21% on power compared to the previous designed intake system.