maxcanada
Mechanical
- Aug 25, 2007
- 2
I saw this topic somewhere else and found it very interesting.
Perhaps it makes sense to hear more from experts' voice in this forum.
"Let's open a thread of discussions on cylinders dieseling. A dieseled cylinder will not operate properly due to burnt holes through the piston seals, requiring to be replaced and repaired.
Dieseling in cylinders is a thermodynamics event referencing the explosion of air pockets and oil vapors that mix together, get compressed to bubble size that are carried on the piston surface- most likely the wear band, and through a low number of cycles accumulate such an internal energy / temperature that the mixture auto ignites, burning holes through seals, or even blowing out metal chunks from the piston, in the vicinity of the O-ring, or seal grove where the explosion happened.
As the title suggests, the phenomenon is similar to the combustion process in a diesel engine, and it needs a couple of elements to happen: Air bubbles, or aeration in the hydraulic system, oil fumes or oil vapors that become a combustible mixture, rapid compression and high velocity reciprocating motion that raises the temperature of the mixture past the oil auto ignition temperature.
The method of troubleshooting and implementing changes, so that such events are avoided or eliminated is as complex as one can imagine.
First, it is worth saying that most likely the big, expensive cylinders from mobile systems are exposed to dieseling, as it is almost impossible to eliminate aeration completely in the hydraulic system. Before getting mad at me for this statement, please consider that a substantial part of the hydraulic circuitry is placed above the free surface of the hydraulic tank, therefore bleeding off air is difficult, and incomplete. Hoses supplying fluid to the head end of the cylinders will be arching close to the top of the machine/cabin level, thus having a high potential of entrapping air. Even if this is not the culprit, or the only one, air can be sucked in the installation through the rod seals, and the discussion can continue.
When the cylinder is cycled at high pressure, and the velocity is high, the thermodynamic cycles seen by the bubble will raise the internal temperature of the mixture very rapidly, reaching within 5 or 6 cycles 500 + degrees F, which is higher than most mineral oils auto-ignition temperature. If you don’t agree with this statement, please run an example using the law of perfect gases.
There are always triggering elements that will make some cylinders diesel, and the ones that I noticed were aeration + high velocity at the end of the stroke.
Floor for discussion: there are many possibilities for air to be entrapped in the system, and responding to this question first, leads to how to troubleshoot dieseling cylinders. It is complex, interesting, frustrating, costly, but in the end very rewarding when the solution finally is found and proven."
The original post I saw is much longer and can also be found in:
Regards
Max
Perhaps it makes sense to hear more from experts' voice in this forum.
"Let's open a thread of discussions on cylinders dieseling. A dieseled cylinder will not operate properly due to burnt holes through the piston seals, requiring to be replaced and repaired.
Dieseling in cylinders is a thermodynamics event referencing the explosion of air pockets and oil vapors that mix together, get compressed to bubble size that are carried on the piston surface- most likely the wear band, and through a low number of cycles accumulate such an internal energy / temperature that the mixture auto ignites, burning holes through seals, or even blowing out metal chunks from the piston, in the vicinity of the O-ring, or seal grove where the explosion happened.
As the title suggests, the phenomenon is similar to the combustion process in a diesel engine, and it needs a couple of elements to happen: Air bubbles, or aeration in the hydraulic system, oil fumes or oil vapors that become a combustible mixture, rapid compression and high velocity reciprocating motion that raises the temperature of the mixture past the oil auto ignition temperature.
The method of troubleshooting and implementing changes, so that such events are avoided or eliminated is as complex as one can imagine.
First, it is worth saying that most likely the big, expensive cylinders from mobile systems are exposed to dieseling, as it is almost impossible to eliminate aeration completely in the hydraulic system. Before getting mad at me for this statement, please consider that a substantial part of the hydraulic circuitry is placed above the free surface of the hydraulic tank, therefore bleeding off air is difficult, and incomplete. Hoses supplying fluid to the head end of the cylinders will be arching close to the top of the machine/cabin level, thus having a high potential of entrapping air. Even if this is not the culprit, or the only one, air can be sucked in the installation through the rod seals, and the discussion can continue.
When the cylinder is cycled at high pressure, and the velocity is high, the thermodynamic cycles seen by the bubble will raise the internal temperature of the mixture very rapidly, reaching within 5 or 6 cycles 500 + degrees F, which is higher than most mineral oils auto-ignition temperature. If you don’t agree with this statement, please run an example using the law of perfect gases.
There are always triggering elements that will make some cylinders diesel, and the ones that I noticed were aeration + high velocity at the end of the stroke.
Floor for discussion: there are many possibilities for air to be entrapped in the system, and responding to this question first, leads to how to troubleshoot dieseling cylinders. It is complex, interesting, frustrating, costly, but in the end very rewarding when the solution finally is found and proven."
The original post I saw is much longer and can also be found in:
Regards
Max
