Are Hydrogen/Natural Gas Mixtures the Answer
to Attaining the 2007 Heavy-Duty Emissions Standard?
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by Jerry Jones
Collier Technologies

While industry’s concentration on zero emissions for 2010 has been primarily focused on hydrogen fuel cells, there is an emerging technology that has proven its ability to meet the heavy-duty 0.2 gms/hp-hr NOx emissions for the upcoming 2007 EPA Standard.  The technology is using a fuel mixture of 30% (by volume) hydrogen, and the balance natural gas (HCNG), in engines modified to optimize performance with the HCNG mixture.  The 30% hydrogen level is used because it represents a level that allows engine operation at or near the “knee” of the NOx reduction curve.

Recently, Collier Technologies, Inc., in conjunction with partners Daewoo Heavy Industries, Ltd. and Hess Microgen LLC, have modified an 11-liter Daewoo bus engine (the City Engine) to yield 300 hp with about 900 ft-lbs of torque, while achieving NOx emissions across its power range of 0.08 gms/hp-hr.  These emissions levels were attained at the exhaust level without any after exhaust treatments.

Hydrogen extends the lean burn limit of natural gas.  While any natural gas engine will yield lower levels of NOx, CO and NMHC emissions when fueled with the HCNG mixture, there is resulting loss of power unless the engine is further modified for higher airflows.  Most OEM engines have significant turbulence in their cylinder heads, as that is desirable for fuels such as diesel, gasoline and natural gas.  As hydrogen is introduced, a quiescent head design becomes preferable.  In addition to reduced emissions levels, the modified lean burn HCNG engines run significantly cooler than the traditional stoichiometric operated engines with EGR and three-way catalysts.   This promises prolonged engine life.

The HCNG mixture has an added benefit, being able to help facilitate development of a hydrogen infrastructure.   CNG fleet operators can add the hydrogen, whether from reformed natural gas or from renewable sources, at the fueling point.   This allows the use of existing CNG facilities with minimal modifications.   The stations will be able to provide pure hydrogen, HCNG or pure CNG fuels to a variety of future fleets.  Over a significant period of time, the HCNG mixture has proven compatible with existing CNG fuel tanks, although with about a 10% reduction in range if added storage is not provided.   There are some positive offsets to the 10% number, due to operating in a lean burn format at higher efficiency levels. 

While the 30% HCNG mixtures and quiescent head designs are subject to patents owned by Collier, the Company has indicated its willingness to license the technology to all major engine manufacturers and assist them in optimum implementation. ©2005. All Rights Reserved. A Publication of the National Hydrogen Association.
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