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Steady state emissions testing on a dynamometer with an 11-liter heavy-duty engine have shown the ability to obtain tail pipe oxides of nitrogen (NOx) emissions of 0.15 g/bhp and below. Equivalence ratios of 0.53 have been achieved over the operating range. The development of a dedicated hydrogen-enriched natural gas (HCNG) engine utilizes a mechanical means to extend the lean limit of combustion through a quiescent intake path. Hydrogen blend ratios of 30-40% have been employed. Current manufactured natural gas heavy-duty engines use intake swirl as a means of extending the lean limit of combustion for reducing NOx emissions. These engines have shown reductions in NOx emissions with HCNG and lean burn however, are unable to meet 2007 goals. Principals at Collier Technologies, Inc (CTI) have been developing and operating HCNG engines for the past eleven years with dramatic results in NOx and CO emissions.

Engine dynamometer testing of homogeneous charge, spark ignition lean burn engines fueled by natural gas, hydrogen/natural gas blends and neat hydrogen was conducted to determine if NOx emissions from blended fuel operation can be reduced below those generated from natural gas operation, approaching those due to a 100% hydrogen fueled engine. The preliminary tests were conducted at the University of Central Florida/Florida Solar Energy Center on an eight cylinder automotive engine. The results indicate that the hydrogen/natural gas fuel has the potential of meeting highly restrictive NOx levels. Sandia National Laboratories conducted follow-on, comparative tests using a single cylinder research engine. The Sandia results indicate that the proposed CARB EZEV standard for NOx can be met without exhaust gas aftertreatment using a 30% hydrogen (by volume) / 70% natural gas blend fuel in a constant speed/power, hybrid vehicle application which achieves 60 MPG gasoline equivalent efficiency.

Engine dynamometer testing was conducted on a production automotive engine. Untreated exhaust emissions were measured over a range of hydrogen/natural gas fuel mixtures and equivalence ratios (Φ). The most important finding was that, with retarded ignition, extremely low raw NOx emissions can be attained at the same time as high brake thermal efficiency. With a 30% hydrogen mixture and Φ = 0.65, the effect of spark timing on engine efficiency is almost negligible over approximately 15° of crankshaft rotation. For an engine load of ∼400 kPa, brake thermal efficiency remained at 30%. NOx emissions can be kept below 0.05 g/kWh for bmeps up to 500 kPa and rpms above 1700, with low hydrocarbons and minimal effect on fuel economy.