In the rally car racing there is a need for maximum power throughout the race. While this is not possible through the entire engine speed range, it is possible to manipulate the engine speed at which maximum power is obtained by changing the engine configuration. One of the most effective ways to do this is to modify the intake system to allow for more air into the engine, thus allowing for more fuel to be burnt and more power to be obtained. This dissertation focused on improving the inlet system of a high-performance rally car race engine by using computational fluid dynamics (CFD) and mathematical optimisation techniques, the combination of which is called a computational flow optimisation (CFO) system. Historically, designers have been aware of the importance of proper intake design and with improving technology and a better understating of wave theory, as applied to manifold flow, development moved at fast pace. The application of wave theory to intakes led to a more academic approach to engine tuning, where mathematical relationships were developed to describe the influence of certain engine parameters on air intake. Numerical methods used to solve for flow in intake systems have also developed due to the advances in computer capabilities and are used in the study in the form of CFD and 1-D gas dynamics (as implemented in the engine simulation code used in the study, namely EngMod4T). These are combined with optimisation to arrive at an improved design. The CFD simulations are transient in nature in order to capture the pulse interactions and their influence on the mass of air inducted by the intakes. The first case considered is that of a single intake exposed to atmosphere. To relate the results of the single intake simulation to a full-intake simulation, the mass of inducted air is assumed to be equal for all four intakes. This assumption was found to be flawed as shown by the simulation that followed that took into consideration all four intakes also open to atmosphere. The simulation showed that the intakes actually induct differing amounts of air and the total amount is less than for four single trumpets. A more comprehensive simulation was conducted where the airbox was included and the resulting total mass inducted showed that even less air is inducted by this setup. The results of the latter were used as the basis of the optimisation study that followed. Various airbox designs, obtained from the optimisation software LS-OPT, were simulated and resulted in an improved airbox design that inducts 6.2% more air than the original airbox. And since there is direct relationship between mass of air inducted and engine power produced, it is expected that the engine power would also increase by 6.2%. The study demonstrates the successful implementation of a CFO system to solve a complex industrial flow problem. With the increase of computing power and increasing affordability of such systems coupled with the ease-of-use of commercial CFD software, CFO should become more common in industrial application.
Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2007.