Application of Hydrogen Assisted Lean Operation to Natural Gas-Fueled Reciprocating Engines (HALO)

Abstract

Two key challenges facing Natural Gas Engines used for cogeneration purposes are spark plug life and high NOx emissions. Using Hydrogen Assisted Lean Operation (HALO), these two keys issues are simultaneously addressed. HALO operation, as demonstrated in this project, allows stable engine operation to be achieved at ultra-lean (relative air/fuel ratios of 2) conditions, which virtually eliminates NOx production. NOx values of 10 ppm (0.07 g/bhp-hr NO) for 8% (LHV H 2 /LHV CH 4) supplementation at an exhaust O 2 level of 10% were demonstrated, which is a 98% NOx emissions reduction compared to the leanest unsupplemented operating condition. Spark ignition energy reduction (which will increase ignition system life) was carried out at an oxygen level of 9 %, leading to a NOx emission level of 28 ppm (0.13 g/bhp-hr NO). The spark ignition energy reduction testing found that spark energy could be reduced 22% (from 151 mJ supplied to the coil) with 13% (LHV H 2 /LHV CH 4) hydrogen supplementation, and even further reduced 27% with 17% hydrogen supplementation, with no reportable effect on NO x emissions for these conditions and with stable engine torque output. Another important result is that the combustion duration was shown to be only a function of hydrogen supplementation, not a function of ignition energy (until the ignitability limit was reached). The next logical step leading from these promising results is to see how much the spark energy reduction translates into increase in spark plug life, which may be accomplished by durability testing.

Effects of hydrogen addition on cycle-by-cycle variations in a lean burn natural gas spark-ignition engine

“…Conventional ways to decrease CCV and strengthen lean burn ability include optimizing the combustion chamber, increasing ignition energy as well as the number of spark plugs [4] and intensifying in-cylinder turbulence [5], all of which have limited effect and certain drawbacks. For example, increasing ignition energy will shorten the life of the spark plug [6] and heavy turbulence is detrimental to volumetric efficiency. A highly effective and convenient way is hydrogen addition.…”

Extending Lean Operating Limit and Reducing Emissions of Methane Spark-Ignited Engines Using a Microwave-Assisted Spark Plug

“…Several researchers have shown that addition of hydrogen increases flame propagation of the air-fuel mixture, extending the lean operating limit and reducing emissions [7][8][9][10][11][12][13][14]. Smutzer [8] developed a hydrogen-assisted lean operation (HALO) engine that achieved operation at ultralean conditions (λ = 2.0), eliminating NO x production and reduced spark ignition energy by 22%. However, nonuniformities in fueling lead to high cylinder-to-cylinder variation in the engine.…”