Gas fuel engine and air / fuel ratio control system for the engine

摘要

An air-fuel ratio control system for a gaseous fuel engine which runs on gaseous fuel containing at least partly hydrogen gas has a fuel supply control valve which adjusts the amount of the gaseous fuel supplied to the engine and a control unit which controls the fuel supply control valve to control the air-fuel ratio according to the engine load. The control unit controls the fuel supply control valve so that the air-fuel ratio becomes higher than a NOx-maximizing air-fuel ratio, at which the amount of NOx emitted from the engine is maximized, in a predetermined operating range of the engine, and in the predetermined operating range of the engine, the control unit controls the fuel supply control valve so that the air-fuel ratio becomes higher in a high engine speed range than in a low engine speed range.