What is disclosed is a micro-
pilot injection ignition type
gas engine, whereby an
air fuel ratio control in starting the engine is executed with enhanced precision, by means of introducing skip-firing intermittent operations which reflect the engine operation conditions, while an idling time span can be shortened or omitted.The engine includes: a gas valve that opens and closes a fuel-gas passage in front of each cylinder, so as to arbitrarily control the
throat area as well as the opening-closing time span of the gas valve; an engine speed detecting unit to detect the engine speed; a
combustion diagnosis unit to detect an engine
combustion state through a
cylinder pressure distribution along elapsed time, as to each cylinder; an opening-closing
control unit as to the gas valve, so as to control the intermittent opening-closing of the gas valve according to the levels of the detected engine speed as well as the
cylinder pressure distribution; whereby, in starting the engine, the intermittent opening-closing of the gas-valve enables at least one skip-firing mode that brings an enhanced fuel-supply pressure-pulsation with which a relatively large amount of fuel-gas is supplied per
engine cycle with firing so that the air fuel-gas ratio of each cylinder reaches a prescribed target value.