Emission Control with Lean Operation Using Hydrogen-Supplemented Fuel

Hydrogen-supplemented fuel was investigated as a means of extending lean operating limits of gasoline engines for control of NO_x. Single-cylinder engine tests with small additions of hydrogen to the fuel resulted in very low NO_x and CO emissions for hydrogen-isooctane mixtures leaner than 0.55 equivalence ratio. Significant thermal efficiency improvements resulted from the extension beyond isooctane lean limit operation. However, HC emissions increased markedly at these lean conditions.

A passenger car was modified to operate at 0.55-0.65 equivalence ratio with supplemental hydrogen. Vehicle emissions, as established by the 1975 Federal Exhaust Emissions Test, demonstrated the same trends as the single-cylinder engine tests.

The success of the hydrogen-supplemented fuel approach will ultimately hinge on the development of both a means of controlling hydrocarbon emissions and a suitable hydrogen source on board the vehicle. Reported efforts to develop a satisfactory onboard hydrogen generator (gasoline reformer) appear restricted by fuel economy considerations.