Many experts agree that hydrogen is the energy source of the future. They also agree that widespread use of economically competitive hydrogen-fueled fuel cells and engines are a decade--and maybe even a couple of decades--away, thanks the to total lack of a hydrogen fuel infrastructure. Besides the large infrastructure investment cost, current fuel cell technology requires 99.999% pure hydrogen that is now not readily available.

Collier Technologies Inc.(CTI), Reno, Nev., views HCNG, a blend of hydrogen and compressed natural gas, as the logical pathway to building this hydrogen infrastructure to make pure hydrogen engines and fuel cells viable.

CTI's licensed HCNG technology was used for what has been designated the "City Engine," a Daewoo natural gas engine modified specifically for transit buses and other heavy-duty transportation applications. The 11 L, six-cylinder, inline engine runs on a mixture of 30% (by volume) hydrogen and 70% natural gas. The water-cooled, four-cycle engine features overhead valves, 10.5:1 compression ratio, spark ignition and an electronic engine control system. Using a stock Daewoo turbocharger, the engine produces 282 hp at 2200 rpm and 866 lb.ft, of torque at 1350 rpm. With an improved turbocharger, CTI expects to be able to produce 300 hp and 900 lb.ft.

Besides adding the hydrogen fuel system components--regulators, lines, tanks, etc.--the primary changes to the engine involve a new quiescent head, plus engine control module programming. The combustion chamber's shape is designed so the engine operates at about a 0.52 to 0.54 equivalence ratio or 1.92 to 1.85 lambda, CTI said.

CTI said the engine has already demonstrated it can meet 2007 emission requirements today by using HCNG technology. The most significant result was the very low 0.08 to 0.14 g/hp-hr emissions of nitrogen oxides across a wide operating range (800 to 2200 rpm). This is well below the 0.2 g/hp-hr standard for heavy-duty engines that goes into effect in 2007 and this was done without any exhaust catalytic treatment. Other emissions were also quite low--less than 1.57 g/hp-hr CO and 1.70 g/hp-hr total hydrocarbons.

The engine also showed improved fuel economy. CTI uses lean burn technology without EGR (exhaust gas recirculation) for charge dilution for lower fuel consumption compared to existing and proposed rich-burn low emission techniques.

The 30% hydrogen mixture allows improved volume and flow characteristics, albeit with engine modifications and lower exhaust temperatures. The latter means increased engine life and reduced maintenance that can compensate, along with better fuel economy, for the higher cost of the HCNG blend compared to natural gas alone. CTI said catalyst costs are significantly less expensive than for competing stoichiometric catalysts. The only exhaust constituents that need reduction are hydrocarbons, and thanks to the 10% oxygen content of the exhaust, an oxidation catalyst is expected to be able to do the job.

While blends of HCNG ranging between 30% and 50% hydrogen allow sufficient hydrogen to significantly enhance the combustion of ultra-lean mixtures of natural gas without extensive engine modifications, CTI said that quiescent head technology is required to achieve ultra low N[O.sub.x]. If hydrogen is simply added to natural gas without modifying the engine control points--i.e., timing and air/fuel ratio--the N[O.sub.x] content will increase. Thus, hydrogen addition, lean burning and quiescent cylinder head flow are all needed to effectively reduce emissions of N[O.sub.x] as well as CO, CTI said. The company said its research has shown that optimum blend is 30% [H.sub.2] and 70% CNG. Further reductions in N[O.sub.x] can result if more hydrogen is introduced, but this leads to diminishing returns in power produced and emission reductions.

The City Engine is now undergoing California Air Resources Board (CARB) certification review. Also, several engines will be used in buses that will be demonstrated in revenue service. The fueling infrastructure for the buses will be supplied by another partner, Trillium USA. CTI, in partnership with Daewoo Heavy Industries and Hess Microgen, plans to produce the engines for urban buses in the U.S. starting in early 2005. An 8 L HCNG engine, also based on a Daewoo NG engine, is under development.

CTI is initially concentrating on using HCNG in larger heavy-duty fleet operations, as it is relatively easy to add hydrogen to existing gaseous fueling stations used for natural gas bus fleets. As the fueling infrastructure for HCNG is put in place, the technology could rapidly be adapted to medium and light-duty applications as well, the company said. This infrastructure can also meet the needs of future pure hydrogen-fueled vehicles.

CTI is also demonstrating HCNG's technological ability to significantly reduce emissions in other engines. For example, in the Hydrogen Bus Technology Validation Program, CTI has converted a John Deere 8.1 L natural gas engine to operate on HCNG in an ultra-lean burn mode to reduce exhaust emissions while maintaining engine power. Also participating is the city of Davis, Calif., the Yolo County Transportation District, University of California-Davis and UniTrans.