PURPOSE: To prevent a heat exchanger from its sulfuric acid corrosion by providing a circuit, bypassing the exhaust gas heat exchanger, in a secondary cooling water circuit and allowing secondary cooling water to flow bypassing the heat exchanger when exhaust gas temperature lowers.
CONSTITUTION: A secondary cooling water circuit 3 provides a circuit 8 bypassing an exhaust gas heat exchanger 1. A three way valve 2 is provided in a branch part of the bypass circuit 8. The three way valve 2, whose opening and closing action is controlled by a quantity-governing rack position of a fuel injection amount, allows secondary cooling water to flow bypassing the heat exchanger in the bypass circuit 8 when exhaust gas temperature lowers. In this way, the heat exchanger can be prevented from its sulfuric acid corrosion with no condensation of steam and sulfur in exhaust gas.
AKIBA HIRONAGA
KANO IKUJIRO
HASHIGUCHI TADASHI
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