Ethanol Flex-fuel Engine Improvements with Exhaust Gas Recirculation and Hydrogen Enrichment 2009-01-0140
An investigation was performed to identify the benefits of cooled exhaust gas recirculation (EGR) when applied to a potential ethanol flexible fuelled vehicle (eFFV) engine. The fuels investigated in this study represented the range a flex-fuel engine may be exposed to in the United States; from 85% ethanol/gasoline blend (E85) to regular gasoline. The test engine was a 2.0-L in-line 4 cylinder that was turbocharged and port fuel injected (PFI).
Ethanol blended fuels, including E85, have a higher octane rating and produce lower exhaust temperatures compared to gasoline. EGR has also been shown to decrease engine knock tendency and decrease exhaust temperatures. A natural progression was to take advantage of the superior combustion characteristics of E85 (i.e. increase compression ratio), and then employ EGR to maintain performance with gasoline. When EGR alone could not provide the necessary knock margin, hydrogen (H2) was added to simulate an onboard fuel reformer. This investigation explored such a strategy at full load, and examined the potential of EGR for ethanol blends at part and full load. This investigation found the base engine torque curve could be matched across the range of fuels at a higher compression ratio. The engine could operate at maximum brake torque (MBT) timing at full load for all but the lowest octane fuel. Fuel enrichment was not needed to control exhaust temperatures, whereby carbon monoxide emissions were drastically reduced. Full load fuel consumption was reduced by 8-10% with regular gasoline (92 RON) and 20-21% with premium (100 RON). Full load brake thermal efficiency (BTE) increased 9.3 percentage points with E85 compared to the base engine. The full load fuel consumption was only 9% higher than the baseline engine even though E85 has ∼25% lower energy content (net heat of combustion) than gasoline.