Abstract: An operation control system for an engine using alcohol fuel or mixed fuel of alcohol and hydrocarbon, or for an engine supplying cooling liquid such as alcohol, water or the like as fuel. Vapor concentration in exhaust gas and an air excess ratio of air-fuel mixture are detected, and a supply rate of alcohol, a water absorption ratio of alcohol or an amount of the cooling liquid is computed on the basis of the vapor concentration and the air excess ratio. Ignition timing, temperature of the coolant, a compression ratio and an air excess ratio are controlled on the basis of the supply rate of alcohol or the water absorption ratio of alcohol. Further, the cooling liquid is supplied which has its amount computed at a heavy load. Thus, operational performance of the engine is improved.

Abstract: A gas sampling valve is provided with a small opening for gas sampling and a gas flow channel communicating therewith and is adapted to sample a gas in the gas flow passage by operating a valve for opening and closing the small opening, wherein at least one detector for detecting the concentration of oxygen or combustion gas is disposed in the gas flow passage, whereby the concentration of oxygen, an air excess ratio, the combustion efficiency, or the like can be measured without using a separate analyzer.

Abstract: There is disclosed a spark-ignition engine having a combustion chamber in which cavities are formed. The cavities are in communication with each other via a communication passage. Air-fuel mixture is appropriately held in the cavities. Spark plugs are disposed near the centers of the cavities to ignite the mixture at plural positions. At the top dead center, the clearance between the top surface of the piston and the lower surface of the cylinder head is made small to minimize useless space. A large squish area is provided to effectively collect the mixture in the cavities. Since the combustible mixture is always held in the vicinities of the spark plugs, stable and rapid combustion can be realized.