|Delphi Multec Direct Injection Gasoline (DIG) Injector.|
Delphi is developing flex-fuel capability for its coming Multec direct injection gasoline (DIG) systems, thereby giving automakers the ability to extend the performance and efficiency benefits of direct injection gasoline engines into a flex-fuel application.
The current Delphi Multec gasoline multi-port injector systems can be used with global gasoline-alcohol mixtures of up to 100% (also factoring in the differing qualities of alcohol fuels in the global market) and on single- or multi-intake valve spark ignition systems.
Delphi fuel rails and Multec 3.5 E85 injectors allow for increased flow capacity for ethanol. Additionally, they are designed with additional resistance to ethanol corrosion. Delphi has supplied E85-compatible technology to more than 2 million vehicles. In South America, Delphi has produced systems and components for more than 430,000 ethanol compatible vehicles since 1991.
The current ethanol direct injection work is to ensure that Delphi’s upcoming DIG system for homogeneous combustion systems (homogeneous charge spark ignited), due to begin production in 2009, will also support global flex-fuel applications.
As [automakers] are responding to the market forces in their markets, higher fuel economy requirements, gas prices and those things, technologies are being implemented onto vehicles such as direct injection engines. Certain manufacturers want to make sure that they can offer the flex-fuel option with those as well.—Michael Frick, Delphi’s Chief Engineer for direct injection gasoline systems
The Multec DIG Homogeneous Combustion Injector features an inwardly opening valve group that can be configured either with a swirl type atomizer for a traditional hollow-cone spray, or with a multi-hole atomizer that provides improved spray stability (cone shape) versus counter pressure.
|The stratified spray created by the DIG Spray Stratified Injector enables fuel combustion to occur with sufficient energy to meet an expanded range of engine performance requirements while helping minimize fuel consumption.|
Delphi will follow this system in 2010 with the introduction of its first spray-guided system, the Multec Direct Injection Gasoline Spray Stratified Injector, which will operate at 200 bar. Its enhanced linear flow range will be suitable for turbocharged engines. The small particles in the spray will optimize charge distribution for future combustion processes such as gasoline homogeneous charge compression ignition (HCCI).
Delphi is taking the approach that material selection for the DIG systems right from the beginning of design has to be compatible with alcohol, according to Frick.
This drives certain decisions such as the use of stainless steel, minimizing the number of elastomers, and putting more attention on the wear surfaces that experience increased forces from increased fuel pressure in a flex-fuel environment.
Ethanol has a higher octane rating than gasoline, and can be used at a higher compression ratio than its petroleum-fuel counterpart. Because of that, even though ethanol has a lower heating value that gasoline, it can actually deliver higher efficiency than a gasoline engine—given the appropriate engine configuration.
For example, a 2002 study by the EPA on the use of 100% alcohol fuels in a port-injected engine found that a turbocharged, 1.9-liter engine with a 19.5:1 compression ratio demonstrated better than 40% brake thermal efficiency with low emissions when using methanol. Ethanol produced similar emissions levels, but with slightly higher fuel consumption.
By way of comparison, Saab’s E100 400hp Aero X concept car (earlier post) uses a 12:1 compression ratio and twin turbochargers running at 1.0 bar boost. Both the Aero X and E100 Saab BioPower Hybrid concept (earlier post) use a Spark Ignited Direct Injection (SIDI) system.
MIT researchers have been investigating the use of a parallel ethanol direct injection (DI) system to support the use of small, highly turbocharged engines with substantially increased efficiency as a downsizing strategy to reduce fuel consumption and emissions. (Earlier post.)
In this scheme, the ethanol direct injection system is controlled separately from the gasoline injection system, and the ethanol is stored in a separate tank. The gasoline system can continue to use conventional port-injection.
The requirements of a flex-fuel system, however, are more constraining than those of running pure ethanol. The engine can’t be fully optimized to run either alcohol or gasoline.
But endowing a more efficient engine technology—such as gasoline direct injection—with the ability to support a flex-fuel application allows the flex-fuel platforms to take advantage of more general improvement in efficiencies provided by that engine technology. In the case of gasoline direct injection, that results in an estimated improvement in fuel economy of between 5% to 15%, depending upon the drive cycle.
Furthermore, researchers are still looking into ways to further optimize a flex-fuel engine for an ethanol blend. Saab introduced a concept Variable Compression Ratio engine in 2000 that, while definitely not a current high priority, is still being investigated, according to a company spokesperson.
Delphi is also interested in seeing if it can use its variable cam phasing system as a mechanism to get some additional small benefit out of the use of a fuel with higher alcohol content.
Siemens VDO, a Delphi competitor, has indicated that its direct injection systems also will be E85 capable.