Effect of hydrogen addition on the energy and environmental performance of a compression ignition dual-biofuel engine

This study evaluates a compression-ignition engine operated on neat diesel (D100), neat hydrotreated vegetable oil (HVO100), and dual-fuel (D–F) modes in which HVO serves as the pilot while the gaseous fuel is natural gas (NG), simulated biogas (BG: 70 % CH 4 /30 % CO 2 ), or hydrogen-enriched biogas (BG + H 2 , 10–30 vol% of the CH 4 fraction). The gas energy share ( G E S ) varies from 0 % to 80 %. Relative to diesel, HVO100 shortens ignition delay, lowering premixed heat release, ensures similar brake thermal efficiency, and lowers CO, HC, NO x , smoke, and CO 2 . In D–F operation, CO 2 in BG dilutes the charge, narrowing flammability and slowing combustion at high λ (>1.9). NO x decreases by up to ∼90 %, but incomplete-combustion pollutants rise sharply (CO up to 14 time, HC up to 6 time), smoke increases by ∼70 %, CO 2 by ∼22 %, and efficiency drops by as much as ∼45 % relative to HVO100. Hydrogen acts as a main factor by widening lean flammability limits, accelerating burning, and stabilizing D–F combustion. With 30 vol% H 2 (HVO_BG + H30), medium-load efficiency approaches that of neat HVO100; CO and HC drop by ∼30 % and ∼45 % versus HVO_BG (though they remain above HVO100), while smoke, NO x , and CO 2 decrease concurrently—by up to ∼80 %, ∼53 %, and ∼12 %, respectively, relative to HVO100. Considering life-cycle effects – biomass CO 2 uptake and oxidation of biogenic CH 4 – hydrogen-assisted dual biofuels further reduce greenhouse-gas impacts compared with fossil diesel. • Dual biofuels: hydrotreated vegetable oil with biogas enriched by 10–30 % vol H 2 . • At flammability, biogas + H 2 dual biofuel achieves neat-fuel thermal efficiency. • In biogas dual-biofuel operation, hydrogen enrichment can raise or lower smoke opacity. • Hydrogen-enriched biogas in dual-biofuel cuts smoke ∼80 % and NOx ∼53 % vs neat fuels. • Hydrogen-aided dual biofuels cut CO 2 ∼12 % and lower GHGs via biogas CH 4 combustion.