[Terrapreta] WET ETHANOL IN DIESEL ENGINES

[Benjamin Domingo Bof]

DIESEL ENGINES
  Contrary to the opinion of most "experts", diesel engines can be run on pure alcohol. The main problem is in the lubrication of the injectors. This is solved by the addition of 5-20% vegetable oil (or other suitable lubricant) to the alcohol. It is also possible to make a diesel "gasohol" with up to 80% alcohol. Since alcohol and oil will not mix when water is present, both the alcohol and the oil must be anhydrous. Different engines may also require adjustment of the metering pump for optimum performance. Diesel engines, especially turbocharged diesels, may also be run with an alcohol/water injection system as described later.

  ENGINE MODIFICATION
  The following are some specific guidelines to assist in the modification of a carburetor. Remember that there are many different types and makes of carburetors, and that a certain amount of experimentation will be necessary.

First, of course, you will have to remove the carburetor from the engine, clean it, and disassemble it to a point where you can remove metering jet(s). This will involve removing the air horn from the float valve and disconnecting any linkage. Next you must locate the main jet (or jets on a multi-throat model). Most carburetors have removable jets. They are almost always brass and are threaded into place.

With the jet removed, the next step is to measure its diameter. This is best done with a micrometer. You will want to enlarge the area of the jet about 27% for ethanol and 40% for methanol. Suppose, for example, your jet is 0.054" in diameter. The formula for the area of a circle is 3.14 (pi) times the square of the radius. The radius is half the diameter, so we multiply 0.027 x 0.027 x 3.14 to get an area of 0.002289 square inches. Multiply this times 1.27 (for a 27% enlargement) and we get 0.00291 square inches. Working the formula in reverse we get a diameter of 0.06087 inches. This is close to a #53 drill which is slightly too small. Since it is easier to enlarge a hole than to make one smaller, a wise choice for the first trial in this instance would be a #53 drill.

Carefully drill out the jet, reassemble the carburetor, and reinstall it on the vehicle. The vehicle should then be run on alcohol as a test. Start the engine and slowly enrich the mixture (using the idle screw adjustment) until the engine starts to stall. Then adjust the idle until the roughness evens out. Take the vehicle for a short test drive, and then pull the spark plugs. If the tips are white, the mixture is too lean, and the main jet will have to be further enlarged. If they are wet, the mixture is too rich, and you have made the jets too large. In addition, if the mixture is too lean, the engine will backfire and miss.

It will also burn the valves if left in this condition. On the other hand, if the hole is too large, the mixture will be too rich and you will waste fuel. It may be necessary to make several trials before the perfect jet size is found for your particular engine. In addition to the main jet, some carburetors will also require a slight enlargement of the idle circuit jet. This is accomplished in the same manner as above except that a smaller percentage of enlargement will usually suffice. Note that this modification isn't always necessary. Often merely backing out the idle adjustment screw will be enough.

If the engine still doesn't run properly, there are several other things you can try such as advancing the timing a little, disconnecting the vacuum advance line, and closing the spark plug gaps a little. If you want to go the whole route, you can increase the engine's compression by milling the head and installing high compression pistons because the alcohol's high anti-knock qualities will allow compression ratios to 10:1. Finally, if you have an engine where it is impossible to modify the carburetor, for one reason or another, (an excess of emission "plumbing", for example) you can usually replace your carburetor with an earlier model. Usually, the older the carburetor, the easier it is to convert. Also, it is possible to purchase adjustable jets for many carburetors, or your carburetor may already have such jets. Adjustable jets make it easier to change from alcohol to gasoline and vice versa should the need arise.

  ALCOHOL INJECTION
  Alcohol injection is a third alternative for the utilization of alcohol fuel. It is similar to water injection except that alcohol or an alcohol water mixture is injected into the engine. Since the water/alcohol injection mixture ratio can be as low as 50/50%, first run product from a simple still can be used. This is a considerable saving because most of the energy used in alcohol production is expended in the distillation stage to obtain 95% alcohol. Another advantage is that engines with an injection system still retain complete dual fuel capability. Finally, alcohol injection can be used with fuel-injected, turbocharged, and even diesel engines.

Figure 3-1: BASIC INJECTION SYSTEM


Figure 3-1 is a schematic of a simple injection system. The alcohol/water mixture is contained in a separate tank and is fed, under a couple pounds pressure, to a misting nozzle located at the throat of the carburetor. The mixture is metered into the carburetor airstream where it mixes with the air and is taken into the engine. There are many ways of metering the alcohol/water mixture. For example, it can be done by mechanically linking a metering valve to the throttle. Other methods include using combinations of vacuum and/or manifold pressure. Whatever system is used, the metering system should work in parallel with the throttle. That is, the flow of alcohol/water mixture should increase as the load increases. Figure 3-2 diagrams a similar system for turbocharged engines. This is an extremely simple system. The alcohol/water tank is pressurized by bleed air from the compressor on the turbocharger. The mixture is metered into the turbocharger airstream by an orifice.

Figure 3-2: INJECTION of TURBO ENGINES


The size of the orifice is determined by individual engine requirement. The metering system operates with the turbocharger. As the boost increases, more pressure is supplied to the tank and, thus, more mixture to the engine.

On a diesel tractor rated at 125 horsepower and consuming 8-1/2 gallons of fuel per hour, the injection system produced the same power with only six gallons of diesel fuel and two gallons of a 50% alcohol/water mixture. This is an overall saving of 6% in fuel consumption and a saving of almost 30% in diesel fuel. Other benefits include trouble-free, automatic operation, increase in available power, lowering of engine operating temperatures, and prolonged engine life.

       
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