Comparing the Performance and Limitations of a Downsized Formula SAE Engine in Normally Aspirated, Supercharged and Turbocharged Modes

This paper compares the performance of a small two cylinder, 430 cm 3 engine which has been tested in a variety of normally aspirated (NA) and forced induction modes on 98-RON pump gasoline.These modes are defined by variations in the induction system and associated compression ratio (CR) alterations needed to avoid knock and maximize volumetric efficiency (η VOL ).These modes included: (A) NA with carburetion (B) NA with port fuel injection (PFI) (C) Mildly Supercharged (SC) with PFI (D) Highly Turbocharged (TC) with PFIThe results have significant relevance in defining the limitations for small downsized spark ignition (SI) engines, with power increases needed via intake boosting to compensate for the reduced swept volume.Performance is compared in the varying modes with comparisons of brake mean effective pressure (BMEP), brake power, η VOL , brake specific fuel consumption (BSFC) and brake thermal efficiency (η TH ).The test engine used in experiments was specifically designed and configured for Formula SAE, SAE's student Formula race-car competition.A downsized twin cylinder in-line arrangement was chosen, which featured double overhead camshafts and four valves per cylinder.Most of the engine components were specially cast or machined from billets.Experimental results showed BSFC or η TH values in the order of 240 g/kWh or 34% could be achieved.TC BMEP values in the region of 25 bar were also achieved, the highest recorded for small engines on pump gasoline [1].The engine was installed into successive Melbourne University Racing (MUR) vehicles in 2003 and 2004, where it was very competitive, finishing first in the fuel economy event at the 2004 Australasian competition.BRAND UniMelb 'WATTARD' TYPE Parallel twin 4 stroke SI, Liquid-cooled, Integral clutch/ transmission CAPACITY 433.8 cm 3 BORE x STROKE 69 x 58 mm FIRING ORDER Unequal (0°, 180° CA) COMPRESSION RATIO 9-13:1 with piston modification COMBUSTION CHAMBER Pent roof, Central spark plug VALVE ACTUATION 8-valve DOHC VALVE TIMING IVO 24° BTDC IVC 72° ABDC EVO 57° BBDC EVC 9° ATDC LUBRICATION Dry sump ENGINE MANAGEMENT Motec M4 EMS CLUTCH Multi wet plate TRANSMISSION Constant mesh (3 forward gears)