Plantoil/diesel conversion basics
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danalinscott

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(Under construction)

Some of the earliest formal studies on the substitution of VO and VO blends for diesel fuel noted that piston/ring/land coking was a serious problem. Since "ring coking" can be noted as it progresses from its early stages to that likely to cause permanent and catastrophic engine damage by charting compression loss this procedure will be discussed here.

As the movement of piston rings..especially the upper ring(which prevents the hot gasses from leaking from the combustion chamber past the piston and into the crankcase) begins to be limited by carbon (coke) accumulations they cease to be as efficient at doing what they are designed to do and more combustion gasses are allowed to leak past the rings. As the efficiency of the rings decreases more gasses leak by and the process of ring coking speeds up...since the gasses carry partially combusted VO fuel into the ring area of the piston.

By charting the values from regular compression tests of a converted engine it can be noted when/if a loss of compression is occurring before the condition becomes critical. Actions can then be taken to prevent the final stages of ring coking thereby reducing the likely hood that the engine will be damaged beyond repair.

To understand what a compression test is go HERE.

Charting compression values begins with establishing a baseline or "benchmark" compression value. This is accomplished by performing a compression test on the engine and adding all of the compression values together.

This number(value) is then recorded along with the mileage or engine hours at the time the test was performed. At  predetermined intervals (miles or engine hours) another compression test is performed and the total compression values recorded.  These values are then charted using a simple charting program or simple graph paper.

This should initially create a chart with a horizontal line if the compression values "points" are connected. As long as the line produced when each compression value "dot" is connected to the previous one any ring coking that may be occurring i snot critical.

However...if the line begins to trend downward it is a signal that carbon accretions are beginning to limit the free movement of the piston rings.  This indicates that the compression ring(s) are no long able to seal in the combustion taking place above the piston as well as before. It is the first warning that ring coking is occurring.

If the downward angle of the line become steeper it is an indication that ring coking is progressing more rapidly and may soon become critical. If any of the individual compression values drops to "out of spec" the engine should be immediately removed from service to avoid major engine damage.   This indicates that the coking in that cylinder has become critical.


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