Spanking Ester

that new car stink

By Leif Forer

More in the Fall 2009 issue

Dear Ester,

I heard some new diesels aren't so good on biodiesel. Or are they? Is this a fuel quality issue?

~Dealing with Every Little Engine-Troubling Emission

Dear DELETE,

This has nothing to do with fuel quality and everything to do with emissions control.
The EPA regulates on-road emissions and they are particularly interested in particulate matter (also known as soot). Now some new diesels are equipped with diesel particulate filters (DPFs, for short) that filter out you-know-what.
My understanding of the problem is that most vehicles equipped with DPFs use a regeneration system called post-injection (or in-cylinder injection). The computer controlling the fuel injection sprays an extra squirt of fuel into the cylinder during the exhaust stroke.
With petro-diesel, this bit of extra fuel vaporizes and travels with the exhaust gasses to the DPF, where a reaction occurs that burns off soot and significantly reduces emissions.
However, there are components in biodiesel with much higher boiling points than diesel fuel.  These components do not completely vaporize and can seep past piston rings into the crankcase oil sump. Slowly, over time these miniscule amounts of unburned fuel that leak past the rings can dilute the crankcase oil.
This problem is easily alleviated by changing engine oil more often than normal.
It is also possible to reprogram the computer that controls injection so that it does not spray that extra squirt during the exhaust stroke. Be advised that, officially, the EPA does not allow this for on-road use.


Dear Ester,

I have some old biodiesel sitting around from last year. At one point it was good stuff, but the jugs have been in the sun now it's old and probably bad. Can I just use it as home heating oil? My furnace doesn't care, right?

~Old Finished Fuel Showing Potential Extra Crappiness

Dear OFFSPEC,

Next time, store those jugs in a dark place.
Biodiesel, like beer, oxidizes in the presence of sunlight. You are right that because the fuel has been sitting around for over six months it would be unlikely to pass the oxidative stability and acid value specs of ASTM D6751. It is always a good idea to retest old fuel to see how far it has wandered out to pasture.
Though I do not have a lick of experience burning biodiesel in home heating furnaces, I suspect that the nozzles on those burners are more forgiving than the high pressure nozzles on your vehicle's fuel injectors.
Burning a lot of this type of off spec material is never a good long term idea because of increased risk of carbon buildup and component degradation. My guess is that blending with diesel fuel to, say, B20 will likely mitigate your problems.

Dear Ester,

How often does a typical biodiesel plant get the full ASTM test done? Every batch? Really?

~A Not Testing Individual

Dear ANTI,

A typical plant probably tests the full spec way too infrequently.
When we started producing at Piedmont we probably ran the full slate on our first 10 production lots, just to confirm that we could hit it consistently. Today we test key parameters on every batch and only run a full slate twice a year or if we make a major change in our production paradigm.
A typical batch at Piedmont runs through the lab at least half a dozen times before it is ready to be sold. We test flash point, water and sediment, moisture, cloud point, acid number, soap, free glycerin, total glycerin, sulfur, oxidation stability, visual appearance, and cold soak filterability on every batch.
Additionally, we run group 1 and 2 metals tests monthly. Testing key parameters on every batch is critical to ensuring that only quality product is released for sale.
It is unrealistic to think that a homebrewer making fuel for themselves would subject each of their batches to all of these tests, let alone the full slate. However, it is very reasonable for a homebrewer to, at a minimum, conduct a simple conversion test (like the 27/3) before any batch is released for washing.  Add a soap, acid number, and water test (e.g. a "Sandy Brae") before releasing it for use.

Ester is Piedmont Biofuels Industrial’s Leif Forer. Send questions to P.O. Box 661, Pittsboro, NC 27312 or Leif@biofuels.coop