Greetings from Japan.🇯🇵 This was a very interesting video that recorded a situation where a diesel engine does not stop immediately even if the decompression is released when it runs out of control. I referred to the service manual for the Lister SL1 diesel engine to understand the series of operations the young man performed in the video. The injection pump control lever of the Lister diesel engine is adjusted so that it starts at the fully open position at 12 o'clock, gradually reduces the rotation by operating it clockwise, reaches the specified rotation at the 3 o'clock position, and stops the rotation at the fully closed position at 4 o'clock. And it seems that decompression is not used directly to stop the engine. Decompression seems to work by forcibly pushing down the exhaust valve to prevent it from closing properly, allowing the compression pressure to escape into the exhaust pipe. 0:03 The young man gradually accelerates the rotation of the flywheel with the starting handle. 0:08 After the rotation speed has accelerated sufficiently, the decompression lever, which was released, is pulled toward the fuel tank to close the decompression. The engine starts, and as the RPM gradually increases, the starting handle is pulled out. 0:14 The injection pump control lever is rotated clockwise from the start position to the normal RPM position, but contrary to what is written in the service manual, the normal RPM position has a higher RPM. From this point, the young man operates the injection pump control lever to the stop position several times, but the rotation does not stop, and he repeats the operation to return it to the normal RPM position. Then, he makes eye contact with the cameraman to show that "something is wrong." 1:30 The engine starts to run out of control due to the damage of the injection pump control lever. At this point, the young man quickly pushes the decompression lever toward the flywheel to release the decompression. However, the RPM is too high and the injection pump is broken with the injection pump over-opened, so the RPM only drops slightly and the engine does not stop completely. 1:43 The engine RPM rises sharply because the decompression lever is operated to the close side when the rotation has not completely stopped. Please note that the exhaust smoke goes from almost clear to thick and the injection pump control lever is broken. From these, it can be inferred that when a diesel engine runs out of control, the fuel supply is excessive and the rotation speed is extremely high, so even if the decompression is released, the compression pressure is maintained due to the reflected pressure from inside the exhaust pipe, resulting in a situation where the rotation does not stop immediately. This is just like the situation where the reflected pressure of the exhaust chamber of a two-stroke gasoline engine creates a "pipe-in". At a construction site in Japan, I used an International Harvester wheel loader produced under license by Komatsu. The engine was stopped by releasing the decompression. The decompression was operated by pulling the throttle pedal toward me with my hand. The engine stopped immediately when the decompression was opened, so this was the first time I had seen a situation like this video where the engine continued to run for a long time even after the decompression was opened. However, after examining this video, I came to understand that "while releasing the decompression is an effective measure when a diesel engine goes out of control, it is important to keep in mind that it takes much longer than usual for the engine to come to a complete stop."
I didn't watch this the first time RU-vid suggested it to me because I didn't want to see a nice old engine die for no reason. I'm relieved to see what the actual outcome was!
