Cetane rating and timing
You're a brave man for experimenting with WMO with one fuel tank.
I salute you!
I like to get my engine up to operating temp on Diesel, then flip it over to the WMO tank. A few minutes/miles before I shut it the engine off, I flip back to the diesel tank so I can start with diesel.
Coking usually occurs at colder temps, and with your timing set too retarded (IMHO) I suspect that doesn't help either.
Another thing I do is to add a little biodiesel to help match the cetane rating of the WMO concoction to that of diesel. The biodiesel has a higher cetane rating than diesel. That is in part what the RUG does too: it has a faster burn rate than WMO or diesel.
The way I see it, there's two ways to match the timing to cetane value of the fuel.
1. Set the timing for the fuel. A real pain when using multiple fuels.
2. Modify the fuel cetane rating to the timing. This can be challenging.
The IDIs are great experimental engines because you can modify the timing. The electronically controlled diesels are a little more difficult.
I mitigate my risk by running only about 50%/50% WMO/Diesel. Actually, 45/5/45 WMO/Biodiesel/Diesel.
From Wikipedia:
https://en.wikipedia.org/wiki/Cetane_number
Typical Values
Generally, diesel engines operate well with a CN from 40 to 55. Fuels with lower cetane number have longer ignition delays, providing more time for the fuel combustion process to be completed. Hence, higher speed diesel engines operate more effectively with higher cetane number fuels.
In Europe, diesel cetane numbers were set at a minimum of 38 in 1994 and 40 in 2000. The current[when?] standard for diesel sold in European Union, Iceland, Norway and Switzerland is set in EN 590, with a minimum cetane index of 46 and a minimum cetane number of 51. Premium diesel fuel can have a cetane number as high as 60.[2]
In North America, most states adopt ASTM D975 as their diesel fuel standard and the minimum cetane number is set at 40, with typical values in the 42-45 range. Premium diesels may or may not have higher cetane, depending on the supplier. Premium diesel often use additives to improve CN and lubricity, detergents to clean the fuel injectors and minimize carbon deposits, water dispersants, and other additives depending on geographical and seasonal needs.[citation needed]. California diesel fuel has a minimum cetane of 53.[3] Under the Texas Low Emission Diesel (TxLED) program there are 110 counties where diesel fuel must have a cetane number of 48 or greater, or else must use an approved alternative formulation or comply with the designated alternative limits.[4]
Alternative Fuels
Biodiesel from vegetable oil sources have been recorded as having a cetane number range of 46 to 52, and animal-fat based biodiesels cetane numbers range from 56 to 60.[6] Dimethyl ether is a potential diesel fuel as it has a high cetane rating (55-60) and can be produced as a biofuel.[7] Most simple ethers, including liquid ones, such as diethyl ether can be used as diesel fuels, although the lubricity can be of concern
