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LESSON 3 What does it take to burn French Fry Oil? If you completed lessons 1 and 2, you should now have a better understanding of how an internal combustion engine works. As you remember, gas and diesel engines differ in several ways but two of the most important differences are:
These two differences are closely related. Diesel engines have much higher compression values in the cylinder than a gas engine. This higher compression is necessary in order to create high temperatures that ignite the atomized fuel when injected into the cylinder. Why? Because a diesel engine does not have a spark that ignites the fuel. It relies solely on the high temperature in the cylinder created by the compressed air to ignite the fuel when it is sprayed into the cylinder. If this sounds complicated, go back to lesson 1 and 2 and look again at the animated images of a gas and diesel engine functioning.
Before we get too technical, let's do a fun
project. This will help illustrate some of the terms I will
use in this class. Project: Homemade Fuel Injection Demonstration As a visual aid, let's make our first project. We'll use a simple spray bottle and some different fluids to illustrate the problem we are trying to solve. Ingredients
An old Windex or other spray
bottle
The night before the test, place a bottle of vegetable oil in the refrigerator. The next morning, take an old Windex bottle with spray nozzle and fill it with water. Make sure the nozzle is set to 'spray' instead of 'stream' and spray it into the air or on the side of a wall. Notice how the water comes out in a mist and leaves a large pattern if sprayed on the wall. The mist you see exiting the nozzle is "atomized" water. This atomization is very similar to how a fuel injector sprays fuel and air into an engine cylinder. Fuel atomization is another way of describing how fuel is sprayed into a mist by mixing the fuel with air. Now, remove the water from the bottle and fill it with some of the vegetable oil from the refrigerator. Now spray that in a different spot on the wall. Notice the difference on how the oil and air exit the nozzle of the bottle. Even though the nozzle was set to "spray" instead of "stream," the fuel probably still exited the nozzle in a bubbly stream. Now go chase your dog, cat or significant other and spray them with the bottle. Are you having fun yet? Back to Class Now, let's talk about what we just witnessed. You saw how the water, when sprayed from the bottle, came out in a fine mist. This is because the water is much thinner than oil or, in other words, the "viscosity" of the fluid was low and therefore thinner. Viscosity is just a fancy term for the consistency of the liquid. The lower the viscosity, the thinner the liquid. The higher the viscosity, the thicker it is.
When you filled the bottle with cold vegetable oil and sprayed it on the wall, there probably wasn't much of a mist. It may have partially squirted or spilled out. In other words, the oil didn't mix very well with the air. This is a rough approximation of the difference between using diesel fuel and vegetable oil in an unmodified vehicle. Somehow, we need to make the vegetable oil thinner so it will spray as a mist into the cylinder and combust to make energy. If the vegetable oil is left at the cold consistency demonstrated, the oil will be sprayed into the cylinder in less than a fine mist. This will cause it to either partially burn with the remainder splattering on the piston or leaking between the piston and cylinder wall. In either case, the oil turns to a carbon film that scratches the cylinder walls or could cause a piston ring to foul and snap. Eventually, this will cause loss of compression or, in the latter case, catastrophic engine failure. An Illustration Let's have a look at another illustration of the properties of vegetable oils. Vegetable oil can sometimes have a consistency similar to butter. When it is frozen, it is hard as a rock. When it is close to room temperature, it is soft but still formed as a solid. When hot, it is a liquid.
Once the butter is a liquid, the hotter it gets, the thinner the liquid. Eventually, it will reach a temperature where the liquid turns to vapor and/or carbon. (ie. burns in the pan) Down to Business Now let's dive a little deeper. In order to use fuel in an engine, we need to get it from the fuel tank to the engine's combustion chamber or from "Point A" to "Point B." Point A is where the fuel is stored. Point B is where the fuel is burned:
So, how do we make the oil 'thinner' so it burns completely? Remember our butter illustration. Butter in the fridge is hard and solid. Put it in a pan and heat it. Now you have a liquid. The hotter the pan gets, the thinner the oil gets until it is hot enough to vaporize. Now let's relate this to a diesel engine. First, we must heat the oil to a temperature where it will flow properly through the fuel lines. Second, we must heat the oil to a higher temperature before it reaches the injectors so it will spray into the cylinder in an optimal pattern for successful combustion to occur. The minimum temperature required for optimal combustion of the veggie oil is highly debated in the SVO community. However, it appears that 160 degrees fahrenheit is a conservative minimum temperature with an upper temperature range of around 190 degrees fahrenheit. Higher temperatures will cause the vegetable oil to thin out and lose its lubricity. (i.e., ability to lubricate the injection pump) To summarize, by heating the vegetable oil to a temperature that changes its consistency to approximately the same consistency of diesel fuel, we can pump the liquid from the fuel tank, through the lines and into the injectors for successful combustion. You Did It! Congratulations! You made it through Lesson 3! At this point, my hope is that you have a working knowledge on how vegetable oil can be used as a fuel in a vehicle. Take a break and then on to Lesson 4 for a primer on building or buying an SVO conversion system!
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