Coal & Coal Biomass to Liquids
Complementary with its work on production of hydrogen and other clean fuels, the Hydrogen and Clean Fuels Program is addressing Utilization of hydrogen in transportation and stationary energy use applications. Fuel cells are expected to be the optimal choice for utilization of hydrogen in both of these applications. However, fuel cell technology has to overcome significant technical and economic barriers in order to establish markets. Hydrogen and hydrogen-natural gas blends may be used directly as fuels for stationary and transportation reciprocating engines that are modified and optimized for these fuels, providing a nearer-term low emissions market for hydrogen until fuel cells are advanced to the point of commercial viability. This approach provides a bridge to future fuel cell usage in transportation applications and is in concert with the goals of the DOE FreedomCar Program.
- Blending hydrogen with natural gas and its use in advanced reciprocating engine types, such as homogenously charged compression ignition (HCCI) engines, coupled with hybrid electric systems, could enable further improvements in emissions and efficiency.
- Conceptually, as the hydrogen infrastructure expands, these same engine systems, with further retrofits and refinements now being developed, could utilize 100 percent hydrogen.
Combustion of mixtures of hydrogen with natural gas allows for leaner operation at lower combustion temperatures leading to lower NOx emissions than use of natural gas alone, while providing enhancements to the combustion process that permit recovery of the power and energy consumption penalties associated with natural gas. The displacement of fuel carbon via hydrogen addition reduces CO, CO2, and unburned hydrocarbon emissions. With 100 percent hydrogen fuel, lean burning may provide ultra-low NOx emissions requiring no NOx after-treatment technology. Further, with no fuel based carbon and reduced oil consumption via a future suitable combination of engine design and oil formulation, oxidation after-treatment may not be required. Complete elimination of after-treatment would provide both an economic and performance benefit.
Research is needed to optimize operation of current engines to use hydrogen and hydrogen-natural gas mixtures, and to minimize emissions of NOx and lube oil consumption while maximizing the distance traveled by vehicles between refueling trips. The program is addressing two broad areas of research:
- Laboratory and computational studies are needed to optimize the ratio of hydrogen to methane in the fuel mixture, based on emissions and engine performance, and
- Computational and laboratory research is needed to address the use of hydrogen/methane mixtures in advanced engines that offer step-out advantages in emissions and performance.
Activities supported by the program in hydrogen storage addressing high-affinity advanced materials such as metal-organic frameworks are scheduled for completion by 2009. The on-going research on metal frameworks shows that their preparation is simple, inexpensive, and can provide high yields. There are other hydrogen storage technologies under study through the Hydrogen, Fuel Cells, and Infrastructure Technologies Program within EERE, such as compressed and liquefied gas storage and chemical and metal hydrides. The Hydrogen from Coal Program is closely coordinating activities with EERE, and will determine the need to investigate other potential storage materials.
Goal and Milestones – Utilization Pathway
Accomplishments and Current Activities
Goal: Complete the small-scale development of hydrogen and/or hydrogen-natural gas mixture engine modifications and operations.
Milestone: By the end of 2009, successfully complete small-scale research to modify and optimize advanced engine types fueled by hydrogen and/or hydrogen-natural gas mixtures.
Previous activities have demonstrated a novel, laser-based ignition system for hydrogen spark ignition engines. This technology offers the potential for further extension of the lean misfire limit and reduced NOx emissions. Current research programs are being conducted on the following topics:
- Optimization of hydrogen-natural gas mixture composition and utilization through laboratory studies of spark ignition engine operation
- Evaluation of hydrogen-natural gas blends as fuel for conventional natural gas engines
- Hydrogen supplementation for natural gas engines at ultra-lean conditions
- Confirmation of feasibility of using hydrogen-natural gas blends to improve performance, efficiency, and emissions of HCCI engines
Specific research projects are listed in the following table.
Other program elements within Hydrogen & Clean Fuels Technology include the following: