Episode 5 – CH3OH

A question everybody asks: Why methanol? Well …

There must be reasons why tractor pullers, drag racers and a lot of other people in motor sports use methanol as a fuel. Time to compare some numbers between diesel, gasoline and methanol. We will use freely available data from the deeps of the internet for this purpose.

fuel_specs

To start with, one can see that it is not evident to find a chemical formula for diesel or gasoline fuels. Diesel and Gasoline are blends of hydrocarbons, with a variety of carbon atoms per molecule, and additives. Thus, it is possible to change the characteristics and behaviour of diesel and gasoline fuels for specific applications and there are marginal changes in the numbers for the heating value or specific weight of theses fuels, depending on your source. For methanol it is easier. Here we have a so-called mono-fuel which only consists of a single type of molecules. The first advantage of running pure methanol is that you can clearly define its chemical behaviour. Methanol can be created, using different methods, including renewable resources like natural gas or bio mass. Using methanol as an alternative fuel, made from renewable resources, results only in carbon dioxide, water and the release of the energy under the form of heat.

methanol

The specific weight of the fuels is not a big concern in our application. It should only be mentioned, that methanol is hydrophilic, which means that methanol mixes with water, compared to gasoline and diesel, which don’t. Therefore, it is easy to stop a methanol fire (tough the alcohol flames are hard to see) because you just mix the burning methanol with water to the point where the solution isn’t flammable anymore. On one side an advantage, on the other side a disadvantage, since the hydrophilic characteristic of methanol lets it mix with air moisture, thus contaminating your fuel with water. Measuring the methanol density, weight per volume, gives you the possibility to check for contaminated fuel. Water is “heavier” then methanol, so the specific weight will rise with contamination.

Most of us know that the “O” in the chemical formula stands for oxygen. Therefore, methanol is an oxygen carrier. This does not mean, that you are able to burn methanol without air, but it brings the disadvantage that methanol is corrosive, since a lot of materials will react with the oxygen in methanol and the products which form during methanol combustion and find the way into your engine. Therefore, care has to be taken when choosing the right materials in a methanol fuel system.

Methanol is not ethanol. Compared to ethanol, methanol and its vapours are highly poisonous and you cannot just mix it with a Coke to have a fun time 😉

Motorsports are about power, so let’s have a look at the energy contained in methanol. Comparing the heating value of methanol one can clearly see, that it is just about half of that from gasoline or diesel … not so good. This only applies, when you burn the same quantity of the fuels! But how many fuel do you have to burn?

Engines not only need fuel but also air. To start let’s think about a piston engine just as being a big air compressor. Without fuel, there is only air pumped through the engine. We are mainly interested in the air quantity aspirated by our compressor during the intake cycle. This quantity is preliminary defined trough the mechanical construction of our engine and will not change when we are changing our fuel. To achieve an ideal combustion, we want to consume all the air (oxygen in the air) during combustion. The quantity of fuel needed to use all the air is expressed as the stoichiometric air fuel ratio of a fuel. This ratio is the mass of air you need to burn one mass unit (kilogram) of fuel. Doing the math, you will find out, that for the same amount of air, you “can” or have to use 2.3 times the quantity of methanol compared to gasoline which results in an increase of nearly 14% in energy fed to your engine. This isn’t economical, but in theory methanol can make more power.

Feeding that much methanol to your engine helps also cool your engine. When you are  heating up a liquid, it consumes heat energy and will eventually change into a vapor state. How much energy it takes to heat up a liquid with a mass from 1kg by one °C (Kelvin to be correct 😉 ) is expressed through the specific heat capacity. The specific heat capacity of methanol is 26% higher compared to gasoline. Considering that you are burning 2.3 times more methanol then gasoline in your engine, methanol takes 2.9 times the energy to be heated up. The energy to heat up the fuel in the engine comes from hot intake air, the engines compression cycle and radiation or surface heat of engine components. Thus methanol “cools” all these elements.

You often hear people talking, that methanol burns faster or slower then gasoline and there is a lot of arguing about this. Let me give you two examples, based on gasoline:

  • Throw a lighted match into a full can of gasoline on a very cold winter day (at your own risk 😛 ). There will probably not happen a lot. Maybe some fuel vapours ignite at your cans opening.
  • Poor half a shot glass of gasoline into a 200 liter fuel barrel filled only with air on a hot summer day. When you come just close to the barrels opening with a lighted match, the barrel, your pants and probably a lot of other vital stuff of you will be gone … so don’t do it at home or at another ones home !!!

It’s all about boundary conditions like:

  • air/fuel ratio
  • temperature
  • pressure
  • fuel state (liquid, vapor)

A lot of stuff to take a deeper look at in future episodes 😉

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