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Old 02-21-2005, 09:40 PM
Kebowers Kebowers is offline
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Join Date: Jul 2000
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diesel fuel performance ratings explained

Diesel No 1 and No 2 refer to the boiling range and viscosity of the fuel. No1 is more like kerosene, and No 2 is heavier (more viscous). No1 will remain fluid without wax crystals to a much lower temperature than No 2.

CENTANE number refers to the ignition quality of the fuel, not the temperature range or viscosity. A low cetane number fuel (say 35) has a long ignition delay--the time from when feul injection starts to when it actually lights off. A high cetane number (say 60) has a very short ignition delay.

Since the base fuel injection timing is fixed (much like ignition timing) the injection pump is set to achieve best performance on a given quality (cetane number) fuel--performance being measured as smoothness, power, smoke emission, etc. The injection timing advances with speed and load to maintin the 'best performance.' Al ot of test stand work goes into determining the advance curve for a given engine. Lots of mechanical things influence the performance.

Higher centane fuel will, for a given engine, tend to run smoother (less diesel knock) with lower smoke. Power may be increased (particularly if the low cetane alternative is lower than what the engine was timed for).

It will not caue any performance deterioration to use high cetane fuel--and it may be beneficial depending on the engine, its condition, and driving habits. Using a fuel with too low a cetane number will cause hard starting, noisy smokey warm-ups, low performance, and lots of 'diesel knock'. Engien damage/destruction will happen if the cetane is too low and the knocking literally breaks things apart.
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