Single Tank Conversions
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Overview
Single tank "conversions" simply use VO in place of diesel fuel in the main fuel tank. This is not really a "conversion" per se, but allows the vehicle to run on VO or WVO. There have been significant reports of engine damage from single tank conversions, especially in moderate and cold climates.
Blending with Single Tanks
VO and WVO are much more viscous than diesel fuel at the same temperature. Blending with solvents to reduce viscosity has its proponents, but the formal studies on this appear to all conclude that simply blending VO/WVO with solvents does not have the same effects as warming VO fuel does. A combination of solvent blending AND warming the VO/solvent blend MAY have different results (and there is some anecdotal evidence of this) but for this page only undiluted VO/WVO is being considered to allow for less confusion.
Heating with Single Tanks
Although there are proponents of simply pouring in VO as a fuel substitute most VO fuel researchers agree that it is much wiser to warm the VO fuel in order to reduce its viscosity and increase it's volatility prior to the Injection Pump and injectors.
In any single tank conversion where the engine or fuel system is to be modified in any way, getting the VO to the target heat range as soon as possible would be of the most benefit.
Arguably, an electric heater such as a VegTherm or a GlowPlug heater would do that faster than coolant heat. However, the IP absorbs most of the heat that is carried to it by the fuel until it reaches operating temp, so pre-IP electric VO heaters may be only marginally more effective, if they are more effective at all, than coolant heated ones.
Apparently how good the glow plugs are in the engine are is very important to the startup and initital running. When the engine is initially started the VO fuel is being injected as very large droplets rather than a mist since no heat is being added to it as it passes through a cold IP or injectors. Even the prechamber is cold and takes a bit of time to warm up to the point it can help vaporize the fuel being injected. In addition to the thick VO significantly retarding the injection timing so fuel injection is later in the compression cycle than it normally would be, the large droplets of VO tend to not combust very completely until the prechamber is fully heated. Until the prechamber heats up, which can take much longer than you might expect, the glow plugs are the ONLY source of significant heat available to aid fuel vaporization. The majority of ring accretions develop during this period of time before the engine is up to operating temperature.
Risks with Single Tanks
When doing a single tank conversion, there are some steps that should be strongly considered:
- Blend with some sort of lighter fuel. During the summer blend around 75% VO/25% diesel.
- Injector line heaters. They heat up very fast, and since before you crank the engine fuel doesn't flow in the injector lines, the first fuel to hit the engine will be relatively hot.
In very cold climates blending may not be sufficient to prevent thickening or crystalization of VO. Since WVO can have high levels of fats or hydrogenation the efficacy of blending may not be sufficient to prevent this even at moderate temperatures with some wvo.
There appear to be several serious problems which have been associated with simply substituting VO for diesel fuel.
- Upper ring land/groove coke deposits.
- Valve accretions.
- Lube oil polymerization.
- Rapid failure of IP due to fuel starvation (the VP44 is likely the most sensitive.)
- Possible lift pump failure due to the added strain of pulling the thicker fuel.
- term papers
