An engine includes an inlet tube introducing air to a combustion process and a first plurality of fuel injectors disposed in the inlet tube and used for scram-jet engine operation. The engine includes a second plurality of fuel injectors used for ram-jet engine operation. The second plurality of fuel injectors is upstream from the first plurality of fuel injectors and is disposed in the inlet tube. The engine includes a combustor swirl zone downstream of and adjacent to the first plurality of fuel injectors.