Author Topic: Interesting experiments on WVO  (Read 14425 times)

oldgoat

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Interesting experiments on WVO
« on: August 22, 2016, 03:11:30 PM »
http://wordpress.ei.columbia.edu/lenfest/files/2012/11/Compression-Ignition-enginer-modifications-for-straight-plant-oil-fueling-in-remote-contexts.pdf        This paper is a bit long but details attempts to tune a CS for wvo and probably only useful for people in warm climates as they replace the C.O.V. with a plug for preheating the fuel.

glort

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Re: Interesting experiments on WVO
« Reply #1 on: August 23, 2016, 07:32:16 AM »

I wonder what the latest thinking on WVO is?
There have certainly been a lot of changes in thinking in the 13 years I have been running it in my vehicles and engines.

I notice they still try to raise the temp of the oil in this study by way of preheating but I feel the testing is somewhat skewed and incomplete.
The say the COV pre heater modification resulted in the injector temp being 90oC but they never specified what the thing was running at BEFORE the HE modification.  They also mention the warmer climates where the engine would be used.  If the oil is over about 10oC, it is plenty liquid and it's viscosity is totally and utterly irrelevant to a mechanical pump. Preheating in cold climates should be done before the fuel filters to ensure adequate flow through the filters and to prevent fats building up on the element if said fats have not been already removed.

I thing the omission of the Injector temp before the modification is deliberate. You can't have an injector bedded in a cylinder head with the resulting thermal transfer taking place and it not be within a degree or 2 of the temp of the head.  There is simply not the fuel flow rate through the injector to influence the resulting heat transfer into the head from the combustion process nor the thermal energy in the coolant.  To assume the fuel flow would cool the injector to any influential degree is ridiculous and every test, ( not that there have been many) I have seen shows the injectors all run around engine temp or slightly hotter anyway.
Heating the fuel and expecting it to have an influence on the temp of which it passes through the injector is nothing short of laughable if one has a clue of the principals involved.

What gets ignored every time with the fuel pre heating theroy is the actual Viscosity range the Pump is rated for in the first place. I have seen those ratings for Bosch inline and Zexcel rotary pumps and their viscosity range upper limits is beyond the point where you you would run out of fuel due to it being too viscious to flow through the fuel lines rather than it causing any problem or strain on the pump.  havign seen the simple and robust working of the simple industrial engine pumps which are all the same in what I have seen, I can only think these pumps would be stronger still. This makes preheating fuel for any reason other than to get it through the fuel filters better and melt out fats a completely moot point unless you are running one of the weaker pumps.

You will then find UNLIKE that is stated in teh study, that heating Veg to any practical temp ( 100oC) still has it several times the viscosity of Diesel and not similar at all as stated in this paper. I notice they supply no evidence to support that remark even like a simple flow test.

Everything I have seen on raising injector pressure has also been shown to be insignificant.  Raising injector pressure does NOT necessarily make any difference to the spray pattern simply because the operating pressures are so high already, only small percentage increases can be made in the first place.  One would not expect a 5% increase in injector pressure would overcome a viscosity difference between Diesel and veg oil which and easily be 800% greater.  Again, on the surface possible, when thinking it through, never going to happen.

The one thing I do agree with is the timing modification.  Oddly, they use more fact and science to show why this works than they did on the other practices which would have shown them to be flawed.

I give low credibility to any test which makes multiple variations and tests them all as one and then says this worked.  Which one worked? Which one made the most difference? How do we know each one made a difference when the test was a batch not an individual trial?

I would put money and a lot of it on the timing alteration making 99 if not 100% of the difference in the results they saw.  It stand to reason.  Veg has lower energy and is harder to ignite which makes it light off later in the compression cycle.  Obviously if an engine is timed for one fuel and you are using another the timing will be less than optimal.  You don't convert a petrol engine to run on gas or alcohol and leave the timing the same if you want the thing to run right.  In the case of veg fuled engine that is exactly what is done because the difference is small and often the difficulty for the DIYer who runs veg is significant.

The thing I have found which overcomes all these problems is simple: The addition of petrol/ gasoline to the WVO.
Petrol makes the veg thinner and does away with teh need for preheating which is not thee when the engine is cold. Electric heating is inffective as the power needed to raise the temp of the fuel flow to the point needed is excessive in a vehicle.
Petrol also brings the timing of the WVO back closer to that of diesel. Petrol will light off much faster due to lower resistance to compression than Veg so initiatiates the combustion earlier in the process helping bring the timing of the WVO burn back earlier than it would light on its own.
My years of use have lead me to believe that 5-10% Petrol is about the right sort of addition.  I have used up to 15% in very cold weather mainly to help with starting with less than ideal oil and have found that 5% in summer works well without causing any vaporisation issues. On that note I have also found that fuels with alcohol are better avoided although that's pretty difficult to do where I am.

The addition of  petrol pretty much takes care of all the basic potential problems of using veg. One could also use higher amounts of Kero or turps but where I am that is much more expensive than Petrol.
Using Diesel is also popular to blend with Veg however as one is starting out where one wants to finish, the end result is really more like making thick diesel rather than thin veg. In order to lower the viscosity you have to start with something thinner than the baseline which in this case is Diesel .

I realise this is an old paper but there are a LOT of basic omissions in it and a lot that also seems to be based on opinion than supporting evidence.
before putting much in any conclusions of that paper, I would want to see the Injector temp before the COV heater mod and also how the engine ran with just that mod, with the higher injector pressure and no other changes and the timing change on it's own.

The basis of any test should be to do one thing at a time and measure it's effect individually yet they failed this most basic scientific principal from the start.