Abstract: A pintle nozzle, preferably an unthrottled pintle nozzle, is provided in which a negative interference angle is formed between the conical tip of the nozzle needle and the mating conical valve seat so that the needle seat is located at the bottom of the valve seat rather than at the top. The resulting nozzle lacks any velocity drop downstream of the needle seat, even at very low needle lifts, so that virtually all of the energy used to pressurize the fuel is converted to kinetic energy. Spray dispersion and penetration at low needle lifts therefore are significantly enhanced. Fuel flow through the converging-diameter discharge passage located between the conical needle tip and conical needle seat also self-centers the nozzle needle at low lifts, thereby helping to assure a symmetric spray and to further enhance spray characteristics.

Abstract: A gaseous fuel injection system for a cylinder of an internal combustion engine assures uniform mixing of the gaseous fuel with an air stream being inducted into the cylinder by injecting the gaseous fuel into the air stream at a relatively high velocity, preferably of between a Mach number of 0.5 and a Mach number of 1.0. High Mach injection can be achieved in a remarkably simple and effective manner by 1) using a single or at most a few injection conduit(s) and discharge orifice(s) for each intake port as opposed to a configuration having multiple discharge orifices at a single point in the air intake system upstream of the intake manifold, 2) by setting the relative effective flow areas of the injector metering orifice C.sub.d A1 and conduit discharge orifice C.sub.d A2 such that C.sub.d A2 is between 2 and 5 times greater than C.sub.d A1, and by 3) setting the gas supply pressure to be more than four times the air intake manifold absolute pressure.