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Intake tuning is a widely recognized method for optimizing the performance of a naturally aspirated engine for motorsports applications. Wave resonance and Helmholtz theories are useful for predicting the impact of intake runner length on engine performance. However, there is very little information in the literature regarding the effects of intake plenum volume. The goal of this study was to determine the effects of intake plenum volume on engine performance for a restricted naturally aspirated engine for Formula SAE (FSAE) vehicle use. Testing was conducted on a four cylinder 600 cc motorcycle engine fitted with a 20 mm restrictor in compliance with FSAE competition rules. Plenum sizes were varied from 2 to 10 times engine displacement (1.2 to 6.0 L) and engine speeds were varied from 3,000 to 12,500 RPM. Performance metrics including volumetric efficiency, torque and power were recorded at steady state conditions.

Bench fuel injection experiments were performed to investigate the levels of generated fuel vapor immediately after fuel injection into a closed vessel. A synthetic fuel mixture was used consisting of six individual fuel components that are representative of gasoline. Vessel (e.g. port) temperature and pressure were varied, as well as sample location and sample delay time after injection. Vessel vapor space samples were collected and processed in a gas chromatograph in order to quantify the contribution to the fuel vapor by the various fuel components. Companion modeling was performed in order to evaluate two fuel vapor mixture preparation models (Raoult's Law and NIST's SUPERTRAPP). Results indicate that approximately 1/6 to 1/3 of the injected fuel mass is in the vapor form immediately after fuel injection (as a function of temperature). SUPERTRAPP modeling indicates that the injected fuel mass is approximately in equilibrium with 6% of the available air.