Effects of Hydrogen Addition on Automotive Lean-Burn Natural Gas Engines: Critical Review

Natural gas (NG) is a gaseous fuel, which has been extensively used and investigated in spark-ignition automotive engines (SI). Combining it with lean combustion has shown the potential to reduce emissions and improve efficiency compared to stoichiometric gasoline engines. The main limitations of lean NG combustion are instability and ignitability. Supplementing NG with hydrogen (H2) is considered a solution to lean NG combustion limitations and it has been studied extensively in the literature. This study is focused on reviewing the work performed by researchers on the effect of partial supplementation of NG by H2 on combustion, emissions and performance of SI automotive engines. H2 addition has been shown to accelerate combustion, extend the lean ignition limit, and improve combustion efficiency. However, it decreases the power output of the engine and increases heat transfer to cylinder walls. The lean ignition limit extension offered by H2 enables increased efficiency and NOx reduction.