Composite dilution effect of exhaust gas recirculation and lean-burn on combustion and emissions of oxyhydrogen/bio-isopropanol/gasoline ternary fuel engine

The complementary utilization of oxyhydrogen and bio-isopropanol in carbon-neutral fuel engines can effectively enhance power output and combustion stability. However, oxyhydrogen blended combustion results in an increase in NOx emissions. To address this issue, this study explores the synergistic mechanisms of lean-burn coupled with exhaust gas recirculation (EGR) in an engine featuring oxyhydrogen negative pressure inhalation (ONPI), bio-isopropanol direct injection (BIDI), and gasoline port injection (GPI). Standard gasoline engines typically face stability limits around λ = 1.1, whereas this ternary fuel strategy achieves stable combustion at λ = 1.2. The experimental findings show that the core operational metrics were effectively enhanced by the composite dilution effect of EGR and mild lean-burn. An OFR of 16 L/min advances the combustion phasing (CA 0–10, CA 10–90) and restores core power outputs (IMEP, Pmax) at λ = 1.1 to the same level as λ = 1 at a specific EGR rate. Meanwhile, operating at λ = 1.1 can successfully lower CO emissions by about 90.4% on average compared to λ = 1. EGR is an effective method for lowering NO emissions. At an EGR rate of 18%, NO emissions are reduced far below the baseline engine level even at OFR = 16 L/min, representing an average reduction of about 84.86% compared to the operation without EGR. However, an excessively high EGR rate can lead to a sharp increase in both the cyclic variations (CoV IMEP ) and engine-out HC emissions. Therefore, the EGR rate must be carefully optimized. Conversely, a small amount of EGR helps to reduce HC emissions and CoV IMEP . In conclusion, “OFR = 16 L/min, λ = 1.1, and EGR rate = 12%” represents the most favorable operational regime for the BIDI + ONPI + GPI architecture. The combination of EGR and lean-burn is a very efficient and clean combustion method.