A compression ignition engine includes a piston having a barrier protruding axially therefrom. The barrier at least partly defines a combustion chamber having a first zone separated from a second zone by the barrier. An initial fuel charge is supplied into the combustion chamber, and a subsequent fuel charge is supplied into the first zone, the subsequent fuel charge having greater reactivity than the initial fuel charge. The fuel charges are compressed to induce ignition and combustion of the fuel charges, such that the subsequent fuel charge burns within the first zone to produce hot gases, and the hot gases flow across the barrier to effect combustion of the initial fuel charge within the second zone.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
 This invention was made with government support under Contract DE-EE0005423 awarded by the U.S. Department of Energy (DOE). The government has certain rights in the invention.