AIR-FUEL RATIO CONTROL METHOD FOR GAS ENGINE

摘要

PURPOSE:To prevent a supercharger from being damaged directly an air manifold pressure from being changed, and air-fuel ratio control from becoming unstable in the case where disturbance is caused by instability of a fuel gas system or combustion. CONSTITUTION:In the case where a rotating speed N of a supercharger exceeds a preset rotating speed NC, a waist gate valve disposed on a bypass passage for bypassing the supercharger is opened to relieve exhaust gas, thus decreasing the rotating speed N (step S4). In the case where the rotating speed N is the rotating speed NC or lower, the waist gate valve is closed, thereby increasing the rotating speed N (step S5). In step S6, an air manifold pressure (AMP) is detected, and an opening/closing valve provided on a relief pipe disposed on an air passage on the downstream side of the supercharger to relieve a part of air if AMP exceeds a preset value AMPC, thus decreasing AMP (step S9). If AMP is AMPC or lower, the waist gate valve is closed, thereby increasing AMP (step 510).