An industry led project with collaboration from the National Renewable Energy Laboratory (NREL), Oak Ridge National Laboratory (ORNL), and the University of Alabama focused on barriers for propane internal combustion engines to adapt to direct fuel injection technology. Direct injection (DI) technology is a barrier for propane engines that are primarily based on spark ignition gasoline engine platforms, which have increasingly shifted from port injection to DI. Research was conducted develop system requirements aligned with potential post-project commercialization for a mono-fuel propane DI engine based on the General Motors 4.3L V6 gasoline platform. After a key project decision point, the project transitioned to a NREL, ORNL, and University of Alabama focused effort focusing on critical high pressure fuel system controls for DI propane, and exhaust aftertreatment research for mono-fuel propane operation, including industry guidance on particulate matter emissions.