To provide a cylinder direct injection CNG engine which implements both stratified combustion and homogeneous combustion in a simple composition.

A CNG engine 10 switching between stratified combustion and homogeneous combustion in accordance with an engine operating condition, is provided with at least a flat piston 12 substantially having no cavity in a top surface, an injector 23 arranged on an intake side in a combustion chamber 10a, and an ignition plug 14 at least. In an injection angle θ of the injector 23, while fuel spray 23a injected at the stratified combustion which is in low load and low rotation ranges is reflected to a flat top surface 12a forming a fuel-air mixture and led to the vicinity of the ignition plug 14, the fuel spray 23a injected during the homogeneous combustion which is in high load and high rotation ranges is led to the vicinity of the ignition plug 14 by utilizing the flat top surface 12a and a cylinder bore wall 11a on the exhaust side while forming the fuel-air mixture.

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