Two key challenges facing natural gas engines used for cogeneration are spark plug life and high NOx emissions. Using Hydrogen Assisted Lean Operation (HALO), these two key issues are simultaneously addressed. HALO operation, as demonstrated in this project, allows stable engine operation to be achieved at ultra-lean conditions and significantly reduces NOx production. For example, at 8% hydrogen supplementation by energy based upon lower heating values, NOx values of 10 ppm (0.07 g/bhp-hr NOx) at an exhaust O2 level of 10% were demonstrated, which is a 98% NOx emissions reduction compared to the leanest operating condition achievable without hydrogen. Spark ignition energy reduction (which will increase ignition system life) was successfully achieved using hydrogen at an exhaust O2 level of 9%, leading to a NOx emission level of 28 ppm (0.13 g/bhp-hr NOx). At this operating condition, it was found that spark energy could be reduced 22% (from 151 mJ supplied to the coil) with 13% hydrogen supplementation based on lower heating values, and even further reduced 27% with 17% hydrogen supplementation, with no reportable effect on NOx emissions for these conditions and with stable engine torque output. Another important result is that the combustion duration was shown to be primarily dependant on hydrogen supplementation, not a function of ignition energy (until the ignitability limit was reached). The next logical step leading from these results is to see how much the spark energy reduction translates into increase in spark plug life by performing durability testing.

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