Multi-point spark ignition engine provided with exhaust recirculation circuit

Claim 1

An engine system comprising: an internal combustion engine of the reciprocating piston type having an intake valve and an exhaust valve for each combustion chamber thereof; an air-fuel proportioning means for supplying a combustible mixture of air and a hydrocarbon fuel to said engine; an exhaust recirculation means for recirculating a portion of the exhaust gas from the exhaust line of said engine to each combustion chamber together with said combustible mixture at a controlled volumetric flow rate relative to the volume of air admitted into each combustion chamber; a thermal reactor provided in said exhaust line to oxidize carbon monoxide and unburned hydorcarbons contained in the exhaust gas from said engine; means for supplying secondary air to said oxidation means; and at least two spark plugs which produce sparks substantially simultaneously for each combustion chamber; said intake and exhaust valves being constructed and arranged such that a substantial overlap of the opening periods of said exhaust valve and said intake valve takes place, so that a substantial portion of the combustion gas is left unexhausted from each combustion chamber; said combustion chamber being defined between the top face of the piston and the bottom face of a cylinder head by a surface of revolution on the longitudinal axis of the cylinder bore; the number of said at least two spark plugs being determined on the basis of a total volume of the recirculated exhaust gas and the unexhausted combustion gas relative to the volume of air supplied to each combustion chamber, said number being two when said total volume is about 50% of the volume of said air at the maximum and three when said total volume is about 60% at the maximum; the spark gaps of said at least two spark plugs being arranged distant from each other in each combustion chamber such that, when the entire area of each combustion chamber in plain view is divided into a plurality of sectors which are in the same number as said at least two spark plugs and of approximately the same area, each of said sectors contains one of said spark gaps.