The diesel engine is the backbone of our transport economy. It is a reliable fuel that can easily be handled, put in a barrel or in a tank where it will sit patiently until you need it, it always works when you need it and its energy dense which means that you don’t need much of it in order to get what you want. That, at least is the assumption. Reality can be different as truck drivers know well.
Diesel is trash. It is a very dirty fuel that produces a plethora of nasty byproducts, all of them deleterious to human health.
For all of those new to the oil business – here is a little primer on what happens in an oil refinery.
Basically, crude oil is being cooked in a cauldron. The oil then separates into vapors and what remains in the kettle. That residue is being called residual fuels and there are different grades of those residuals based on sulfur content and viscosity.
The vapors then enter a column. Those condensing at the highest point of the column are very volatile fuels such as Naphtha and light gasoline. Naphtha and gasoline are called the light distillates. They are the best and cleanest liquid fuels. They just need a little more than 100 degrees Celsius to remain vaporous. They are also called the sweet cut.
Ethane, Propane and Butane (the LPG’s) are escaping through a vent in the ceiling of the column. They are gases at ambient conditions but will condense into a liquid at light pressures.
Below those light distillates and above the residuals comes a Middle Distillate, Kerosene. It’s the stuff burned up in jet engines (this is actually mostly JP54 or a modified form of Kerosene but that goes too far). Kerosene is an oily liquid that will stay liquid up until about 200 degrees Celsius.
Right below that, at around 300 degrees Celsius, Diesel condenses into a liquid. This is very heavy distillate fuel that will not ignite when exposed to a spark. It also requires elaborate spraying into the combustion chamber of an engine as it is so heavy. It’s the heaviest distillate fuel and was originally only considered to be of value as heating oil and stove oil. The diesel engine was a technological masterpiece but that came at a heavy price.
Here comes a little Wikipedia: Petroleum-derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffin’s including n, iso, and cyclo paraffin’s), and 25% aromatic hydrocarbons (including naphthalene’s and alkyl benzenes). The average chemical formula for common diesel fuel is C12H23, ranging approximately from C10H20 to C15H28.
In human language that means that diesel is a ragtag mix of rather long hydrocarbon molecules with a very high carbon to hydrogen ration (that’s bad as this produces more CO2 per energy unit produced). It’s the stuff in the column that just about evaporates but it remains on the bottom of it- because it is so heavy.
Is diesel then the only way to fuel heavy vehicles and machinery? By no means. Early trucks were fuelled with gasoline as it was the much more obvious fuel. The diesel engine was always a technology hog, so it was not for everyone right at the beginning.
Why have we gone for diesel then? Well, for a starter there is much more of the stuff than gasoline. The heavier fractions dominate a barrel of crude. Depending on where it comes from and what grade of crude you have, there will be more or less light products after refinery treatment. The biggest lump will still be the residuals and the biggest distillate lump is diesel. Again, depending on what grade is refined at the moment one will get more or less light products but one thing is always certain. There is more of the heavy stuff than of the light stuff.
But the heavy stuff (diesel) is also very energetic as a fuel and is therefore excellent for long haul and heavy duty transport. It produces great torque which makes those engines really powerful. Their only inconvenient – they are really, really dirty.
Seen under the microscope, diesel is no seamless liquid like water. It’s more a collection of droplets averaging in sizes of about 80 to 120 nanometers. Those droplets are pretty hard to vaporize in the combustion chamber which makes any diesel burn incomplete by nature as the fuel incinerates in concentric rings at the surface of the droplet (we had that in another post, you remember?).
That’s the birth of Fine Particles, as the concentric burn produces a kernel in the middle of the droplet. This kernel is then evacuated through the vehicle exhaust straight into our lungs causing cancer and a plethora of other nasty diseases. Also, because diesel burns very hot it produces a lot of Nitrogen Oxides, also very deleterious to human health. Sulfur also combines with Oxygen producing Sulfur Oxides which then produces acid rain.
Besides, Middle Distillates are never free from non-oil substances – a bewildering array of heavy metals and sulfur among others. All those substances are found in the particulates that diesel engines emit.
Now you will tell me that since modern diesel vehicles are equipped with particulate filters, the problem with particulate emissions is gone. To a point, you are almost right. They are not emitted into the air anymore but they still clog up the filters after the engine and once those are exchanged, the old ones need to be disposed of which means a lot of toxic substances that have to be taken care of. Just take a look at the picture on top of this post.
Diesel fuel is – in fact – garbage from the refining process. We wanted more of the lighter substances as they are cleaner and easier to use but we just did not get enough of them so we made diesel work for us. And surprise, surprise – we got so used to diesel that we found many little advantages in this toxic brew so it almost hits us as something romantic. For a while it was cool to burn diesel.
But a fuel with so many nasty substances in it and which is producing so many more when it is burned up, is nothing but toxic sludge. And let’s be frank, diesel is only valuable because the world got hooked on it. Illegal drugs are expensive to get as well not for their inherent qualities but because they are hard to get. Diesel is needed in huge volumes and its harder and harder to get to the stuff that allows producing it in the first place – crude oil.
We burn diesel because once it was cheaper. Now it got expensive because it is still an oil product and hence traces its price developments. But its garbage and it’s about time that we recognized this fact by applying penalties for its use in order to incentivize the use of much cleaner alternatives such as Methane gas and Liquefied Methane (known to many as LNG).
Diesel and LNG are often compared but the comparison itself is almost an insult to LNG as they could not be more different. Methane is a gas that does not produce any Particulate Matter or Sulfur Oxides in the first place. No heavy metals or other nasty stuff to filter as the stuff is just not in the fuel in the first place. And everything else can be brought down to almost nil with a little applied common sense without producing immense amounts of toxic waste that will linger for millions of years. And in today’s high oil price world – it’s even cheaper to not burn trash anymore.
It’s time to stop garbage incineration on roads and in the air. Diesel is toxic waste and it’s a shame that the world in the 21st century still is addicted to this filth.