Ethanol Direct Injection Technology Could Rival Diesel at Less Cost

Flexible-fuel vehicles operating on a blend of gasoline and ethanol reduce the use of fossil fuels. However, this comes with a fuel economy penalty of about 30 percent because of ethanol’s lower energy content. This could be overcome by directly injecting ethanol and gasoline separately into the combustion chamber to optimize the use of both fuels.

Ford is developing an E85 direct injection boosting system that’s combined with gasoline port fuel injection (PFI). This brings higher fuel economy because the gasoline, with its greater heating value, is primarily used during most driving modes. Directly injecting ethanol into the cylinder suppresses knock because of the evaporative cooling effect on the air-fuel mixture. Suppressing knock allows increasing compression ratio to gain additional power, plus higher boost pressures can also be used in turbocharged or supercharged engines. These advantages allow smaller engines to provide performance equivalent to larger engines running without the technology.

The technology was first proposed in 2005 by John Heywood and colleagues at MIT. In 2006, the MIT team founded Ethanol Boosting Systems LLC to commercialize the concept. Ford’s development work is being done in collaboration with EBS and has demonstrated the technology in two engines – an early prototype 3.5-liter EcoBoost engine outfitted with PFI and a 5.0-liter PFI engine in a Ford F-150 pickup truck.

Anti-detonant injection, usually using a 50/50 mixture of water and alcohol, is a technique that’s long been used to allow higher compression ratios and eliminate pre-detonation. For instance, it was used in turbocharged cars like the Saab 99 Turbo before the advent of intercooling and is commonly used in aftermarket turbocharger and supercharger installations.

Because the E85 and gasoline are not blended as they are in a flexible-fuel vehicle, ethanol boosting requires separate gasoline and ethanol tanks along with the need for dual fueling. This is an approach already used with many clean diesel engines that incorporate Selective Catalytic Reduction (SCR), which requires injection of a water and urea blend that’s stored in a separate tank.

Ricardo in Detroit is developing a similar technology it calls Ethanol Boosted Direct Injection (EBDI) to take full advantage of ethanol’s best properties – higher octane and higher heat vaporization. The EBDI project is a collaboration between Ricardo, Behr, Bosch, Delphi, Federal Mogul, GW Castings, and Honeywell. A prototype 3.2-liter V-6 EBDI engine can operate on pure gasoline or up to 100 percent ethanol. By adding other advanced technologies like direct injection, variable valve timing, optimized ignition, and advanced exhaust gas recirculation, it’s possible to produce more power than with gasoline alone.

Both Ford and Ricardo say their technologies allow gasoline engines to deliver performance, economy, and durability levels competitive with diesel engines, but at a lower price. According to Ricardo, the company is able to reduce engine displacement by 25 to 50 percent while not only delivering torque that is competitive with direct-injection diesels, but fuel economy as well.

Ford’s E85 DI + gasoline PFI, like modern diesel engines, features turbocharging, direct injection, more substantial construction to handle the higher pressures, and complex controls. However, there are several important differences that make DI + PFI a cost-effective approach, including the fact that the DI + PFI engine requires a relatively inexpensive conventional three-way catalyst. The E85 DI + gasoline PFI engine also uses a renewable fuel in a leveraged manner to significantly reduce petroleum consumption and total net CO² emissions. Likewise, Ricardo’s EBDI technology relies on affordable and well-established three-way catalyst after-treatment technology to meet EPA emissions regulations.

Ricardo predicts that by 2015, EBDI-equipped engines could become a major force in the medium duty commercial truck and off-highway markets including agricultural and construction vehicles.