ページタイトル

Chapter 1 to 2

コンテンツ

1. Features of Engine for Portable Fire Pumps

For a portable fire pump, compactness, lightness and high output are indispensable. That’s reason why a 2-cycle gasoline engine is adopted.
This is the point significantly different from ordinary 4-cycle automobile engine. Features of 2-cycle engine, which is most suitable for a portable fire pump, are as follows.

   (a)  Since engine fires per turn of crank shaft,
           * Rotation is smooth.
           * Output is powerful, about 1.5 times that of four-cycle engine. 
           * Size is small with relatively large output.  

   (b)  Since there are neither intake nor exhaust valves,
          * Structure is simple.       * Adjustment is easy. 
          * Less trouble.                * Light weight.   
        * Less engine noise.
   (c)  Since mixed oil is used,
          * After start-up, it can immediately go into high speed operation.
          * Troublesome oil change is not required.
          * Less trouble without using oil pump.

2. Operation of 2-cycle gasoline engine

As the figure shows, 2-cycle engine completes one-cycle per revolution of crankshaft. In other words, while piston moves up and down (2 strokes), 1 cycle of intake, compression, firing and exhaust is completed.

After piston passes top dead center, explosion force will act on top of piston and expansion will start. Expansion occurs in cylinder, and intake port will close at crank case side, and compression stroke will start inside case. Exhaust port will open inside cylinder and combustion gas will be exhausted, and cylinder internal pressure will suddenly drop.
Scavenge port will open, and new mixed air pre-compressed in  crank case will enter into cylinder and push out exhaust gas. When piston passes bottom dead center, scavenge port will close and decompression in crank case will start. Exhaust port of cylinder closes, and compression stroke starts. Crank case internal pressure will drop more.
Compression will take place inside cylinder, and intake port of  crankcase will open, and new mixed gas will be sucked by negative pressure inside crank case.

2-cycle Port Operating / Closing Timing
External circle: Inside of cylinder.
Internal circle: Inside of crankcase.


<< Contents Chapter 3 to 4 >>

pageTop

【参】BSI-EN:フッターナビ