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The Story Of Diesel

It’s something we hear about our think about just about every day, whether we drive a diesel-powered vehicle or a petrol-powered one.  There you are, pulling up at the local bowser and you have to stop and do a quick check to make sure that you get the right one, diesel rather than petrol or vice versa.  You probably don’t stop to think about the word diesel much or the history behind it.

Most of us think that diesel engines are called diesel engines because they run on diesel. After all, a petrol engine runs on petrol (which, for you word boffins out there, is short for petroleum, which is derived from the Latin petra oleum, translated “rock oil”).  However, this isn’t the case.  We call the fuel diesel because it was what went in a diesel engine, i.e. the sort of internal combustion engine invented by Herr Rudolf Diesel back in 1893.  If you want to be picky, what we use is “diesel fuel” which we put into a diesel.

The story of the diesel engine starts back in the days of steam.  Steam power, though a major breakthrough that transformed the world and took us into the era of machines rather than relying on muscle power, was pretty inefficient.  You needed a lot of solid fuel to burn and you needed water that could be boiled to produce the steam, and you needed to build up a good head of steam to get the pressure needed to drive the locomotives, paddle steamers and machines.  Steam was really inefficient – up to 90% of the potential energy was wasted – and it was pretty bulky (think about steam trains, which need a caboose or a built-in tender to carry the fuel and water).  The hunt was on for something that could provide the same type of oomph and grunt but with less waste (and possibly less space).

In the 1890s, a young engineer named Rudolf Diesel came into the scene and started work on developing a more efficient engine. One of his earlier experiments involving a machine that used ammonia vapour caused a major explosion that nearly killed him and put him in hospital for several months. Nevertheless, in spite of the risks, Diesel carried on, and began investigating how best to use the Carnot Cycle. His interest was also sparked by the development of the internal combustion engine and the use of petroleum by fellow-German Karl Benz.

The Carnot Cycle is based on the First and Second Laws of Thermodynamics, which more or less state that heat is work and work is heat, and that heat won’t pass of its own accord from a cold object to a hotter object. This video gives a very catchy explanation of these laws:

The Carnot Cycle is a theoretical concept that involves heat energy coming from a furnace in one chamber to the working chamber, where the heat turns into work because heat causes gases and liquids to expand (it also causes solids to expand but not so dramatically). The remaining heat energy is soaked up by a cooling chamber.  The principle is also used in refrigerators to get the cooling effect.

Diesel’s engine was based on the work of a few other inventors before him, as is the case with a lot of handy inventions.  Diesel’s engine was the one that became most widespread and proved most popular, which is why we aren’t putting Niepce, Brayton, Stuart or Barton in our cars and trucks.  In fact, we came very close to putting Stuart in our engines, as Herbert Ackroyd Stuart patented a compression ignition engine using similar principles a couple of years before Rudolph Diesel did.

The general principle of a Diesel engine is that it uses compressed hot air (air gets hotter when it’s compressed, which is why a bicycle pump feels hot when you’ve been using it for a while) to get the fuel in the internal combustion engine going.  This is in contrast to a petrol engine (which we really ought to call an Otto engine, as it operates on the Otto Cycle rather than the Diesel Cycle), which used sparks of electricity to get the fuel and air mix going. Petrol engines compress the air-fuel mix a little bit – down to about 10% of its original size, but a diesel engine, the air is compressed a lot more tightly. More details of how it works would probably be better described in a post of its own, so we’ll save the complicated explanation for later.

Diesel fuel doesn’t need to be as refined as what goes into petrol engines, which is what makes diesel engines a bit more efficient than their equivalents that run on more refined petrol (makes you wonder why “petrolheads” are considered to be coarse and crude).  The fuel is more energy-dense and it burns more completely – and it needs less lubrication, which means less friction, which is also more efficient.

Herr Diesel’s original idea was to have his engine run on something that wasn’t this fancy petroleum stuff, which was mostly used medicinally to treat headlice at that stage.  The first prototype used petrol as we know it.  Later models used the cheap fraction that now bears his name.  Even later refinements ran on vegetable oil, with the grand idea that people could grow a source of fuel rather than mine or drill for it.  One of the great mysteries of the story of diesel is why they switched to fossil fuels when the peanut oil that Diesel raved about worked so well.  Now we’re all excited about biofuels and especially biodiesel once again…  Was there some conspiracy at work?

However, how diesel engines came to run on fossil fuels rather than plant oil is not the only mystery about Rudolf Diesel.  His death was also unexpected and mysterious.  In late 1913, this German inventor was on his way by ship to the UK for a conference.  One night, he headed off to his cabin and asked the stewards to wake him early in the morning.  However, he vanished during the night, leaving his coat neatly folded beneath a railing.  Ten days later, his body, recognisable only from the items in his pockets, was pulled from the sea.

How his body came to be found floating in the English Channel is a mystery.  Perhaps the problems with his eyesight left over from his accident with the ammonia vapour explosion and a rough sea led to an accident. Perhaps he committed suicide, as a lot of the fortune his invention had earned him had gone into shares that devalued.  Or perhaps foul play was at work. After all, in 1913, tensions were building between Diesel’s native Germany and the UK, where Diesel had planned to meet with engineers and designers for the Royal Navy.  This was the era of the Anglo-German Naval Race, where the German and British navies were in an all-out arms race to get control of the economically important North Sea.  When Diesel was making his ill-fated crossing, the Germans had the use of the more efficient diesel technology but the British had the formidable Dreadnought class of steam-powered battleships.  The arms race was officially over, as Germany had agreed to tone things down in order to placate the British – who had alliances with the two other political powers that were at loggerheads with Germany.  It’s perfectly possible that in spite of this and because of the political tension of the time, the idea of the firepower of the Dreadnought combined with the efficiency of the diesel engine was just too much for Kaiser Bill’s government…

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