The act of injecting or throwing in; -- applied particularly to the forcible insertion of a liquid or gas, by means of a syringe, pump, etc, a method of inserting fuel into internal-combustion engines by directly forcing the liquid fuel into the combustion chamber at an appropriate point in the piston cycle; in contrast to carburetion, in which an air-fuel mixture is drawn in by the downward stroke of the piston, the forceful insertion of a substance under pressure