In order to avoid environmental pollution, the blow-by gas of the engine is circulated to a gas-intake route of the engine without ejecting the blow-by gas of the engine to the atmosphere. Then, in such a blow-by-gas-circulation pipe line, in order to prevent the moisture and the like contained in the blow-by gas from attaching to or freezing at the inner wall portion of the pipe line, conventionally, there is widely used a blow-by gas heater.
FIG. 6 is a schematic perspective view showing a conventional blow-by gas heater (corresponding to FIG. 11 of Japanese Patent Application Publication No. 2012-215137), and FIG. 7 is a schematic cross-sectional view showing an example wherein the blow-by gas heater in FIG. 6 is provided in a blow-by-gas circulation passage (corresponding to FIG. 9 of the Japanese Patent Application Publication No. 2012-215137).
As shown in FIG. 6 and FIG. 7, a metal pipe 55 which becomes a passage of the blow-by gas includes a smooth wall portion 55d and a partially cylindrical wall portion 55e (see FIG. 6). Therefore, a cross-sectional opening shape of the metal pipe 55 has a partially circular shape. A tip of the smooth wall portion 55d and a tip of the partially cylindrical wall portion 55e form a common opening end face of the metal pipe 55, and a whole tip of the smooth wall portion 55d becomes a last portion 55c of an opening face of the metal pipe 55, and a center portion of the tip of the partially cylindrical wall portion 55e becomes a forefront portion 55b of the opening face of the metal pipe 55 (see FIG. 6 and FIG. 7). The smooth wall portion 55d is disposed in such a way as to face a heating source 56 which is an electronic ceramic heater through a heating-source attachment pipe 54. In the heating source 56, electric power is supplied through a plug member 57.
Also, the metal pipe 55 includes a throttle portion 55f formed such that a cross-sectional opening area thereof becomes smaller toward a tip side.
As shown in FIG. 7, a protruding portion 55a of the metal pipe 55 is disposed in such a way as to protrude to a gas-intake-passage axis-line side al more than to an inner wall face 61d in a connecting pipe 61. Moisture or oil of the blow-by gas attached to the metal pipe 55 flows to a tip side thereof (downward) through the protruding portion 55a so as to promote the moisture or oil of the blow-by gas to become a water droplet or an oil droplet.