Performance and emissions of natural gas/hydrogen blends in large-bore spark-ignition engines

Abstract

Natural Gas is an promising alternative fuel for spark ignition engines because of its high knock resistance and low CO₂ emissions compared to gasoline. Blending Natural Gas with a fuel of higher flame velocity such as Hydrogen (H₂) is desirable since it reduces the carbon intensity of the fuel and results in lower emissions and improved efficiency. Moreover, Hydrogen improves the lean burning capacity of Natural Gas (NG) engines. Additionally, blending Hydrogen with Natural Gas provides a potential solution for Hydrogen transportation. In this study, Natural Gas/Hydrogen blends on a large-bore, two-stroke, spark ignition engine are investigated with Hydrogen concentrations of 0, 10, 15, 25 and 30 % by volume under lean burn conditions. The blends were tested at three different operating conditions i.e., 40, 60 and 70 % of the rated load. The results indicated that the addition of Hydrogen led to shortened burn durations and reduced Coefficient of Variations (COVs) of Indicated Mean Effective Pressure (IMEP) for all the loads. The maximum reduction in COV was observed at 40 % load with a decline of 23 % points. For the remaining loads, the COVs dropped below 4 %, indicating a very stable combustion with 30 % Hydrogen blend. The indicated thermal efficiency (ITE) improved with the addition of Hydrogen and is maximum at the highest Hydrogen concentration. The ITE improved by 3.9, 5.9 and 5.8 % points for 40, 60 and 70 % loads respectively. There is an improvement in NOx, CO₂, CH₄ and VOCs emissions with the addition of Hydrogen. The maximum reductions observed are 95, 17, 70 and 49 % for NOx, CO₂, VOCs and CH₄ emissions respectively. The only exception is CO emissions which increased at 40 % and 60 % loads but decreased at 70 %. The Natural Gas/Hydrogen blends will be tested with varying spark timings and relative air-to-fuel ratios to further enhance the impact of Hydrogen addition on the emissions, efficiency and combustion stability.