Search Results

Restricting the flow rate of air to the intake manifold is a convenient and popular method used by several motor sport disciplines to regulate engine performance. This principle is applied in the Formula SAE and Formula Student competitions, the rules of which stipulate that all the air entering the engine must pass though a 20mm diameter orifice. The restriction acts as a partially closed throttle which generates a vacuum in the inlet plenum. During the valve overlap period of the cycle, which may be as much as 100 degrees crank angle in the motorcycle engines used by most FSAE competitors, this vacuum causes reverse flow of exhaust gas into the intake runners. This, in turn, reduces the amount of fresh air entering the cylinder during the subsequent intake stroke and therefore reduces the torque produced. This effect is particularly noticeable at medium engine speeds when the time available for reverse flow is greater than at the peak torque speed.

The objective of the study outlined in this paper was to optimize the performance of a 600cc four-cylinder FSAE engine through the use of one-dimensional simulation. The first step in this process was to validate a baseline model of the engine in its stock, unrestricted format. This was achieved through the use of crank-angle-resolved and cycle-averaged test data. The in-cylinder pressure history was also analyzed to provide combustion and friction data specific to this engine. This process significantly improved the correlation of the model with the test data and it was subsequently used to simulate and optimize the configuration of the engine planned for use in the 2008 FSAE competition. The process of validating the model, together with the specification of the subsequent optimized engine, are presented.