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Comparing the Performance and Limitations of a Downsized Formula SAE Engine in Normally Aspirated
| Content Provider | Semantic Scholar |
|---|---|
| Author | Attard, William P. Watson, Harry C. Konidaris, Steven Khan, Mohammad Ali |
| Copyright Year | 2006 |
| Abstract | This paper compares the performance of a small two cylinder, 430 cm 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 (ηVOL). 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 PFI The 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, ηVOL, brake specific fuel consumption (BSFC) and brake thermal efficiency (ηTH). 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 ηTH 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. INTRODUCTION In recent times, research into SI engine downsizing has grown in popularity [2,3,4] as governments begin to limit carbon dioxide (CO2) emissions and consumers strive for cost savings due to rising oil prices. Thus, manufacturers are trying to improve performance and efficiency while meeting legislative pollutant emissions standards. Downsizing, defined as a reduction in the engine swept volume with performance retained by intake boosting, appears to be a major way forward in satisfying consumer and manufacturer requirements. However, for downsized engines to be comparable to their larger counterparts, the specific output performance must be increased by a ratio equal to the reduction in engine size [3]. This high specific output can only be achieved with the help of increased engine speeds and/or intake boosting. This increases the induced amount of air and fuel, thus enabling the performance of the downsized engine to be improved to match its larger counterpart. Turbocharging seems to be the most acceptable solution to meeting the requirements, with high pressure ratios achievable and well documented improvements in efficiency [4,5,6,7,8]. TC downsized engines also offer other benefits besides obvious efficiency gains. Engine packaging and overall powerplant weight reduction is improved, which further enhances vehicle efficiency and dynamic performance. Smaller engines also offer mass reductions in engine out exhaust emissions, with reduced need for stratified lean burn strategies to improve efficiency. Thus legislative specific emission standards can be met using conventional after treatment methods (three-way catalyst) at stoichiometric operating conditions. However, disadvantages also exist with smaller downsized engines. The increased specific output places greater strain on the internal components of the engine due to the increased combustion and inertia loading associated with intake boosting and increased engine speeds. This increases the cost and complexity as there is a need to redesign internal components using improved materials and manufacturing processes. More elaborate control systems are also needed to prevent component failure. These measures are required to ensure reliability and durability over the engine’s life cycle, resulting in increased costs. The higher pressures and temperatures associated with TC engines also increase the occurrence of uncontrolled combustion, mainly knock in the end-gas region, which further deteriorates engine performance and reliability [6,9]. BRAND UniMelb ‘WATTARD’ TYPE Parallel twin 4 stroke SI, Liquid-cooled, Integral clutch/ transmission CAPACITY 433.8 cm 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) The original intent of this development program was to achieve success in Formula competition by using a far superior engine package when compared to conventional OEM based motorcycle units. However, from the research and development process, results from this small engine operating in a variety of modes has significance in defining the limitations for small downsized gasoline engines. For instance, is the performance limited by engine mechanics, deliverable manifold absolute pressure (MAP) levels, normal or abnormal combustion or a combination of these factors? Results may give some insight to the extent by which engines can be downsized and the specific areas where future research should be directed. This has significant relevance to manufacturers, who continue to strive for swept capacity reductions, while maintaining performance with improved efficiency. |
| File Format | PDF HTM / HTML |
| DOI | 10.4271/2006-32-0072 |
| Alternate Webpage(s) | https://minerva-access.unimelb.edu.au/bitstream/handle/11343/34450/66989_00002548_01_2006-32-0072.pdf?sequence=1 |
| Alternate Webpage(s) | https://minerva-access.unimelb.edu.au/bitstream/handle/11343/34450/66989_00002548_01_2006-32-0072.pdf?isAllowed=y&sequence=1 |
| Alternate Webpage(s) | https://doi.org/10.4271/2006-32-0072 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
