Multiple spark ignition internal combustion engine with exhaust gas recirculation

A multi-cylinder, spark-ignition, automotive internal combustion engine capable of stable operation with low nitrogen oxides emission levels and improved fuel economy, comprising:

• (a) a plurality of cylinders, a piston reciprocably movable within each said cylinder, whereby in each cylinder the cylinder walls, the head of the piston and the cylinder head define a combustion chamber;
• (b) means for supplying air and fuel comprising gasoline to the combustion chambers at an air-fuel ratio of between about 13:1 and 16:1 to form a mixture in the combustion chambers;
• (c) means for recirculating to the combustion chambers exhaust gases from the engine as a function of the operating conditions of the engine within the limits of stable operation of the engine, the amount of exhaust gases recirculated being from about 25 to 40% of the air supplied to each combustion chamber under engine operating conditions of maximum exhaust gas recirculation;
• and
• (d) a plurality of spark plugs disposed within each combustion chamber for igniting the air-fuel mixture containing the recirculated exhaust gases at points and propagating flame fronts, whereby stable operation, low nitrogen oxide emission levels and enhanced fuel economy are achieved.

A method of reducing the level of nitrogen oxide emissions (NO.sub.x) in the exhaust during operation of a multi-cylinder, spark-ignition, automative internal combustion engine having a plurality of cylinder bores in each of which a combustion chamber having a plurality of spark plugs is defined by a cylinder head and a piston crown, comprising the steps of:

• supplying air and fuel comprising gasoline to the combustion chambers at an air-fuel ratio within the range from about 13:1 to 16:1 to form a combustible air-fuel mixture therein;
• recirculating exhaust gases from the engine combustion chambers back to said combustion chambers at a rate which varies as a function of engine operating conditions and which, as a percentage by volume of the air supplied to each combustion chamber, varies up to a maximum rate of about 50% and which is greater, under substantially all engine operating conditions, than a rate defined by an upper limit of stable operation under corresponding engine operating conditions of an engine, corresponding in structure to said engine having a plurality of spark plugs, but having only a single spark plug;
• and
• igniting the air-fuel mixture containing the recirculated exhaust gases at a plurality of points in each combustion chamber by said plurality of spark plugs, whereby the air-fuel mixture with exhaust gases therein burns at a rate effective to maintain stable operation of the engine while maintaining the level of nitrogen oxide emissions low with improved fuel economy relative to said corresponding engine having a single spark plug.