Pre-chamber ignition system having igniter with gas orifice structured for pre-expanding outgoing combustion gases

A gaseous fuel engine comprising:

• a supply of gaseous fuel;
• an engine housing having a main combustion chamber formed therein, and a main piston movable in the main combustion chamber;
• a gaseous fuel admission valve fluid connected to the supply of gaseous fuel, and coupled to the engine housing to admit gaseous fuel by way of one of intake injection or direct injection into the main combustion chamber;
• an ignition system including an igniter having an igniter housing coupled to the engine housing, the igniter housing having a combustion pre-chamber formed therein, and an igniter tip having a gas orifice formed therein and fluidly connecting the combustion pre-chamber to the main combustion chamber;
• the igniter further including an igniter piston movable within the igniter housing between a retracted position and an advanced position, the igniter piston defining a centrally located axis of reciprocation and having a piston end face;
• the igniter further including an actuator structured to apply an actuating force to the igniter piston to move the igniter piston from the retracted position to the advanced position, and a biaser biasing the piston in opposition to the actuating force;
• and
• the gas orifice having a flow area that is increased between the combustion pre-chamber and the main combustion chamber to pre-expand outgoing combustion gases of an ignition charge of fuel and air autoignited in the combustion pre-chamber;
• the piston is movable a travel distance from the retracted position to the advanced position to increase a pressure of the ignition charge of fuel and air to an autoignition threshold;
• and
• the combustion pre-chamber is unobstructed, such that the centrally located axis of reciprocation extends through the unobstructed combustion pre-chamber from the piston end face to the igniter tip, and the gas orifice continuously fluidly connects the combustion pre-chamber to the main combustion chamber throughout the travel distance of the igniter piston.

A method of operating an engine comprising:

• conveying a gaseous fuel admitted by one of intake injection or direction injection, and air, into a main combustion chamber in the engine to form a main charge of the gaseous fuel and air in the main combustion chamber;
• moving an engine piston in the engine toward a top dead center position to increase a pressure of the main charge of the gaseous fuel and air within the main combustion chamber in a compression stroke in a four-stroke engine cycle of the engine;
• forming an ignition charge in a combustion pre-chamber in an igniter from gaseous fuel and air of the main charge conveyed from the main combustion chamber into the combustion pre-chamber based on the moving of the engine piston;
• moving an igniter piston in the igniter toward an advanced position to increase a pressure of the ignition charge within the combustion pre-chamber to an autoignition threshold;
• conveying combustion gases of the ignition charge through the gas orifice in the igniter to the main combustion chamber;
• igniting the main charge within the main combustion chamber by way of the combustion gases of the ignition charge;
• pre-expanding the combustion gases within the gas orifice;
• limiting a velocity of the combustion gases after exiting the gas orifice, by way of the pre-expansion of the combustion gases within the gas orifice, to less than a threshold velocity for engine mis-fire;
• and
• fluidly connecting the main combustion chamber to the combustion pre-chamber by way of the gas orifice continuously throughout the four-stroke engine cycle of the engine.