Straighter-than-straight vegetable oils as diesel fuels

Michael Allen
Visiting Professor
Prince of Songkla University

Message to the Biofuels-biz mailing list, 8 October 2002

Some background on Southern Thailand agriculture

Two-wheeled diesel tractor running on SVO in Thailand
Here in southern Thailand the major agricutural products are rubber (and rubber-wood) and palm-oil. Prawns are grown in ecologically disastrous ponds when the price is right. Rice is not extensively grown locally because the climate produces only two good crops a year.

The highly photogenic Asian water-buffalo has been largely replaced by the diesel-powered two-wheeled tractor.

Fishing is also a sizable industry and uses diesel engines attached to a long-shafted propeller (the "long-tail") for in-shore fishing or big grunty diesels in purpose-built vessels for long-line squid fishing etc.

Farmers and fishermen have experimented with SVO and SVO blends with kerosene for many years now but both refined coconut oil and refined palm-oil can be sold at a price which is comparable with diesel. Reliable facts on pollution and engine damage produced by crude vegetable oil (CVO ... Crook Vegetable Oil?) experimentation are hard to come by due to the general enthusiasm of the proponent entrepreneurs who are naturally somewhat coy about discussing their failures.

In August 2000, I was asked if "straight" palm-oil could be used to run diesel engines. Based on some work with which I was associated in New Zealand, I assured my colleagues at the Prince of Songkla University that it could. (Hell! We had fired up diesels on butter and biogas in New Zealand! I was on a sure thing here!)

So we ran a Kubota diesel on 50:50 SVO:petrodiesel, then 80:20 and then 100:0. Based on this, we applied for financial support to find out just how much refining was (un)necessary to make an acceptable diesel fuel. Over a year, we ran seven diesel engines on palm-oil: three were in field tests on actual tractors or fishing boats, one was in a home-made truck which delivers fertiliser off-road, and three were in test-beds here at the University. They were all identical in design: And they all had to be run in on petro-diesel because they were all equally new.

In the test beds, we used a standard test based on the Japanese standards for agricultural diesels. (I don't have the designation to hand.) The only engine modification was to bring the exhaust out through the fuel tank and fit a small plastic tank and associated valves to start up the engine (and shut it down) on petrodiesel. We measured fuel economy under a variety of engine loads (achieved with an alternator and electric light bulbs.) We looked at air pollution and volumetric efficiency amongst other parameters. After 500 hours of continuous use, we shut them down, took them to bits, re-weighed the engine pieces (valves, pistons, rings, bearings) and examined them visually.

And now the bit that you are all interested in: The engines worked just fine on refined palm oil. That is oil which has been de-gummed with phosphoric acid and had fatty acids removed by saponification with sodium hydroxide. Yes folks! Sadly, you do need some chemicals and simple process engineering to make most vegetable oils work. Just because you don't do it in the back-yard doesn't mean that it has not been done -- perhaps in one of those big centralised processing plants we all despise :-)

We discontinued the trial after 2000 hours of running (with the engine hardly missing a beat). Now, as I said, the process of refining puts the finished product into a price category comparable with the retail price of petrodiesel (including some tax). In Thai currency, this is about 12 to 13 baht/litre with diesel oscillating around 14 to 16 baht/litre depending somewhat on who the US is threatening today.

To the oil farmer, his crude palm oil (CPO or perhaps CVO if you prefer to distinguish it from the SVO even though it is actually "straighter than straight" ) may be worth only 2 or 3 baht/litre so quite obviously, the less refining needed, the more competitive it should be (at least in an economic sense). But CPO may contain between 2 and 14% Free Fatty Acids (FFA) whereas refined palm oil contains less than 1% (usually about 0.5%). CPO is like "Brasso" metal cleaning fluid -- yellow and waxy with suspended stearin. Refined palm oil is a clean and bright liquid.

Carrying out the comparable continuous engine trials with CPO, our first engine lasted less than 300 hours before it packed in with a big cloud of black smoke and an even bigger bang. Dismantling the engine showed erosion around the inlet port and on the piston head itself. The rings were worn and CPO in the lubricating oil had apparently polymerised to a thick black treacle. So we refurbished the engine with new parts from the maker, replaced the oil, ran it in on petrodiesel and repeated the experiment. This time it almost made it to 550 hours before the same thing happened.

Looking for suitable low-tech solutions which the farmer or a village co-operative could work with, I explored the use of a centrifuge to remove the stearin. (It was implicated in the erosion problem along with the FFA and it tended to block the fuel filter.) Well, leaving aside the question of whether a centrifuge of the cream separator variety is really low-tech, density differences between CPO and stearin were too small to get separation without close temperature control.

And so we came to biodiesel. As it happens, there are several 1 tonne units operating already in this area of Thailand (though I doubt that they comply with anyone's Health & Safety Regulations). They, of course, use waste cooking oil as their feedstock. And the technology is indeed more complicated than simply squishing the stuff out of a handful of palm-nuts in a low-tech press. But it is quite comparable with the process needed to refine CPO into SVO.

This year we have been concentrating on processes which will produce a decent fuel from high free fatty acid crude palm oils. I think we have succeeded. (In part due to Keith and "Journey to Forever" which gave us a head start.) Anyway, we are just starting our engine tests on a bunch of new motors and The New Fuel.

So dear friends, please be careful when you compare that lovely (but already refined) SVO with biodiesel. SVO is indeed a great fuel, particularly for old fashioned stationary engines with a fixed load, eg diesel electric generators or pumps for water irrigation. But you are kidding yourself if you think that the oil or coconut palm actually provides it in the form and composition that you need for this task.

Jatropha, Jojoba and Soy may be much more obliging in this respect but I can assure anyone interested that you will be unable to back up your ute to a palm-tree for refuelling in at least the next couple of years. But I also want to assure you that, even as we speak, we are working on it!

Michael Allen

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