reducing the temperature difference between the housings and suitable for multi-rotor engines such as 4-rotors, etc. However, manufacture of the rotor housjng is made difficult due to its closed passage of cooling water. Therefore, in general, the axial type is used for automobile engInes.
The vicinity of the spark plug hole exposed to heavy heat load js provided with ribs and fins effectively arranged for increasing its radiating area. Higher flow speed of the cooling water also raises cooling efficiency. The low temperature area in the vicinity of the intake port is rather heated by the cooling water, instead.

Thus, the wall temperature can be averaged over the housing and, at the same time, the mixture is preheated to increase vaporization and atomization.
To raise such effects, high temperature exhaust gas may be further led to the low temperature area of the housjng. 


Figs. 3.39 and 3.40 show the cooling water passages within the housing of the circumferential and axial flow water cooling systems for the housing, respectively.
In the circumferential flow type, the cooling water runs independently of each housing, being capable of