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Schematic shows the basics of Delphi's hydrogen enrichment system, slated for production mid-decade. By reformulating a small amount of gasoline in to hydrogen gas, the unit can be used to cut catalyst light-off time in half, and increase the lean-burn tolerance of conventional internal combustion engine designs.
Hydrogen is the fuel of the future, though how it will be produced is still a question to be solved, as is whether fuel cells or internal combustion engines–or both–will use this elixir. While those questions remain unanswered, Delphi has found a new use for hydrogen–reducing start-up emissions, and advancing lean-burn engine technology.
"This isn't an off-the-shelf technology," says Dr. Jean Botti, chief of technology at Delphi, "it's something that still needs to be developed, but it should be in production vehicles by mid-decade." Delphi's hydrogen enrichment system is straightforward. An on-board catalytic fuel reformer about the size of a 12-ounce can, and with a maximum volume of one liter, creates a hydrogen-rich gas by partially oxidizing gasoline diverted from the fuel tank. Control valves regulate fuel flow to the reformer, and gas delivery from the reformer to either the intake manifold, or the catalyst. The system's small size means it can be located almost anywhere in the vehicle, though most applications will likely see it placed in the engine compartment.
"The hydrogen-rich intake charge creates a better flame front," says Botti, "because the mixture is much more flammable. This produces lower engine-out emissions." Hydrogen is a natural byproduct of fuel combustion, but a portion is trapped in the form of hydrocarbons on the cylinder wall.
Creating a hydrogen vapor and spraying it into the engine makes it easier to combust the incoming air-fuel mixture, greatly reducing wall wetting. "And hydrogen injection has another benefit," says Botti, "it can be utilized to heat the catalyst up much faster than normal." Delphi estimates a catalyst warm-up time of 20 seconds could be cut in half by adding this system, and allow a 50% reduction in the precious metals found in the catalyst; a significant cost reduction to the OEM. "Tighter emission standards are going to increase the load on catalysts, which normally means more precious metals are necessary," Botti says, "but we think this technology will mitigate those costs." It also should ease or eliminate the need to increase catalyst package size in order to meet the tighter standards, particularly on larger engines, and make it easier to reach SULEV (Super Ultra-Low Emission Vehicle) standards.
The on-board reformer, however, will have uses beyond start-up emission reduction. "The hydrogen uses very little gasoline, but allows a lean mixture to be used by making the engine more tolerant of lean-burn conditions," says Botti. "We are looking at putting up to 30% EGR (exhaust gas recirculation) back into the engine, which will easily compensate for the small amount of fuel we use to create the hydrogen in the first place." So, on the fly, a hydrogen enrichment-equipped vehicle could call on the unit to improve dynamic emission performance, giving automakers greater calibration flexibility. "We believe this technology will allow OEMs to run lean-burn combustion longer, and over a broader range of driving conditions," says Botti.
Of course, this leaves one very important question unanswered: What will this technology cost? Even though few changes will be necessary to current powertrains in order to add the hydrogen enrichment system, adding the on-board reformer will not come with-out a cost. "You have to be at the same cost level or less than conventional SULEV technology," says Botti, "which requires the use of two or three catalysts per vehicle. I think it is reasonable to expect that hydrogen enrichment will be less expensive than this, and thus be very attractive to automakers, while being transparent to the end user."