Impact of Hydrogen Assisted Lean Operation (HALO) on Natural Gas Engine Combustion

Two key challenges facing natural gas engines used for cogeneration are spark plug life and high NO_x 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 NO_x production. For example, at 8% hydrogen supplementation by energy based upon lower heating values, NO_x values of 10 ppm (0.07 g/bhp-hr NO_x) at an exhaust O₂ level of 10% were demonstrated, which is a 98% NO_x 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 NO_x emission level of 28 ppm (0.13 g/bhp-hr NO_x). 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 NO_x 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.