Following completion of a competitive procurement, ULA has selected Blue Origin's BE-4 engine for Vulcan Centaur's booster stage. The liquefied natural gas (LNG) fuelled booster will be powered by a pair of BE-4 engines, each producing 2.45 MN (550,000 lbf) of sea level thrust.

Source: United Launch Alliance selects BE-4 engines for Vulcan