Ethanol Flex-fuel Engine Improvements with Exhaust Gas Recirculation and Hydrogen Enrichment, 03-R9751Printer Friendly Version
Inclusive Dates: 09/01/07 01/01/08
Background - The Energy Independence and Security Act of 2007 increased the corporate average fuel economy to at least 35 mpg by 2020 and maintained tight emissions standards. The Energy Policy Act of 2005 requires gasoline producers to nearly double the production of renewable fuels by the year 2012, and require federal dual-fuel fleet vehicles to operate exclusively on alternate fuel, typically E85 (85 percent ethanol, 15 percent gasoline). The implication of such legislation is that ethanol flex-fuel vehicle production volumes will continue to increase along with domestic production of ethanol. In the 2007 model year, there are more than 30 flex-fuel vehicle models available, and an estimated 5 million on U.S. roads. The main drawbacks for consumers using E85 are the scarcity of fuelling stations and the higher fuel costs to operate an eFFV (ethanol flex fuel vehicle) on E85. The number of E85 filling stations has grown exponentially from year 2000 (133) to 2007 (more than 1200), but is still marginal compared to the approximately 167,000 retail gasoline stations in the U.S. The higher cost to operate on E85 will persist until the ratio of gasoline cost per gallon to E85 is approximately 1.35, due to the lower energy content of E85 (based on 2007 EPA fuel economy estimates). Gasoline and E85 prices are driven by a multitude of market forces and government subsidies, but improving fuel consumption for eFFV is an attainable objective. In general, the strategies for improving fuel consumption for gasoline engines such as turbocharging and EGR (recirculated exhaust gas) can be applied to eFFV engines. Doing so has the potential to provide eFFV fuel economy on E85 that can approach the fuel economy of the original gasoline counterpart.
Approach - An investigation was performed to identify the benefits of cooled EGR when applied to a potential eFFV engine.The fuels investigated in this study represented the range a flex-fuel engine may be exposed to in the United States; from E85 to regular gasoline. The test engine was a 2.0-L in-line four cylinder that was turbocharged and port fuel injected. 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 on-board 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.
Accomplishments - 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 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 to 10 percent with regular gasoline (92 RON) and 20 to 21percent with premium (100 RON). Full-load brake thermal efficiency increased 9.3 percentage points with E85 compared to the base engine. The full load fuel consumption was only 9 percent higher than the baseline engine even though E85 has approximately 25 percent lower energy content (net heat of combustion) than gasoline.