Saturday, April 18, 2009

Hydrogen Engine

Hydrogen-fueled internal combustion engines (H2ICEs) are a potential near-term option and bridge to hydrogen fuel cell vehicles. H2ICEs with near-zero emissions and efficiencies exceeding today's port-fuel-injected (PFI) engines have already been demonstrated. In addition, H2ICE-powered vehicles can potentially use the existing manufacturing infrastructure for petroleum-fueled ICEs.

Efforts are focused on developing an advanced spark-ignited engine with efficiencies approaching that of a high-efficiency diesel engine, PFI-like power densities, and emissions that are effectively zero. Direct-injection (DI) H2ICE is one of the most attractive options since it has the potential to avoid many problems associated with the use of hydrogen in premixed and PFI hydrogen engines, such as preignition and backflash. In addition, in comparison to a premixed or PFI H2ICE, a DI H2ICE avoids the power-density loss associated with the displacement of air by lighter hydrogen because fuel is injected after the intake valve has closed. For comparison, a DI H2ICE can deliver approximately 115% the power of a gasoline-fueled ICE at stoichiometry. The challenge with DI H2ICEs, however, is that in-cylinder injection requires H2/air mixing in a very short time (approximately 5 ms at 5000 rpm). Incomplete mixing can produce misfire, high NOx emissions, reduced efficiency, and power loss.

Researchers in the CRF's H2ICE laboratory are initially focusing on the measurement and analysis of in-cylinder hydrogen mixing processes in a DI H2ICE. The laboratory houses an automotive-sized single-cylinder engine (~0.6 liters/cylinder) that provides extensive optical access for application of advanced laser-based optical diagnostics to study fundamental in-cylinder engine phenomena. The engine head is a pent-roof, four valve, center-spark, and side-injection type. Hydrogen injection is through a high-pressure (max. 200 bar) gaseous injector. Researchers plan to use two separate but complementary planar laser-induced fluorescence (PLIF) measurements that provide spatially resolved quantitative measurements of in-cylinder mixing. In the first set of experiments, hydrogen is seeded with a trace amount of acetone; in the second set of experiments, intake air is seeded with a trace amount of NO. The acetone and NO PLIF measurements provide an independent measure of local fuel-to-air ratio. The technique will allow evaluation of injection strategies and chamber design on hydrogen mixing in-cylinder, providing necessary data for optimizing the design of a DI H2ICE. Future research directions will include investigations of pre-ignition, NOx production, and other combustion issues associated with hydrogen-fueled engines.

No comments:

Post a Comment