A significant amount of harmful emissions pass unreacted through catalytic after-treatment devices for IC engines before the light-off temperature is reached, despite the high conversion efficiency of these systems in fully warm conditions. Further tightening of fleet targets and worldwide emission regulations will make a faster catalyst light-off to meet legislated standards hence reduce the impact of road transport on air quality even more critical.
This work investigates the effect of adding hydrogen (H2) at levels up to 2500 ppm into the exhaust gases produced by combustion of various oxygenated C2-, C4- and renewable fuel molecules blended at 20 % wt/wt with gasoline on the light-off performance of a commercially available three-way catalyst (TWC) (0.61 L, Pd/Rh/Pt - 19/5/1, 15g). The study was conducted on a modified naturally aspirated, 1.4 L, four-cylinder, direct-injected, spark-ignition engine. The experiments were performed at the steady-state condition of 1600 r/min and BMEP of 3.6 bar, derived from a time-based load distribution of a WLTC cycle simulation, with levels of gaseous pollutants, particulate matter and hydrogen measured both upstream and downstream of the TWC.
Low-level H2 addition reduced the TWC light-off temperature of CO, THC and NOx, and decreased the time to reach steady particulate number/ mass levels post-TWC. The presence of C2- (ethanol, acetaldehyde, diethyl ether) and C4- (1-butanol, butyraldehyde, 2-butanone, methyl tert-butyl ether) molecules displayed minimal impact on the conversion efficiencies relative to operating the engine with pure reference gasoline. Linalool and γ-valerolactone blends displayed a slight increase in light-off temperature and produced elevated levels of particulates pre and post catalyst, while 2-methylfuran and 2-methyltetrahydrofuran blends emitted lower levels of particulates. Hydrogen levels post-converter were found to reach almost full conversion after H2 light-off, independent of the amount added, however after CO light-off the conversion of the additional H2 was reduced significantly.