The digital engine concept uses direct injection into cavities or subdivisions of the combustion chamber. The subchambers trap fixed quantities of air and the appropriate amount fuel is then either injected or not injected into the subchambers. One of the advantages of this approach to fuel management is that the fuel injection system can be simplified since it is only required to inject one quantum of fuel.The results presented are for a prototype quantum injection system which uses a high pressure source of hydraulic fluid. Experimentation with this system has demonstrated most of the fundamental operation. However, additional work is required before the system is ready to be installed on a digital engine.