Diesel engines have had a long and somewhat complex history, even compared to other internal combustion engines.
The idea and fundamental underpinnings of what became the diesel engine was initially developed by Rudolph Diesel in 1892 as a way of developing a much more efficient engine than the currently reigning steam engines of the era.
His idea was to compress air to such a degree that it would produce enough heat to cause the fuel to ignite, creating the process that makes the engine move and continue to move.
It was primarily known as a locomotive engine, used largely on large vessels, for construction equipment and eventually to power heavy goods vehicles.
The Rise Of The Modern Diesel
It took until the original Volkswagen Golf in 1976 for diesel engines to gain some level of interest as a compact, efficient engine for smaller vehicles and equipment, with an eruption in popularity starting in the 1990s.
The reason for this came with the development of increasingly sophisticated turbo-diesel engines as well as electronically controlled direct injection, which allowed for much more refined, powerful engines which emitted far less carbon dioxide.
This was timely, as in 1997 the Kyoto Protocol was signed which set binding emissions reduction targets for many developed countries, averaging out to a 5 per cent reduction in carbon emissions.
Many countries, but especially the United Kingdom, turned to diesel engines to help make the difference, with then-Chancellor of the Exchequer Gordon Brown proposing that diesel engines should be taxed at lower rates compared to petrol due to producing less carbon dioxide.
This eventually becomes law in 2001 and led to a rapid increase in sales of diesel car sales, to the point that by 2013, over a third (34.5 per cent) of all roadgoing vehicles use diesel engines, although this would lead to a major issue just two years later.
The Dawn Of Euro 6 And Adblue
Concerns about diesel emissions have been around for a long time, but it was believed that thanks to increasingly stringent standards, with Euro 5 standards launching in 2009 to mandate the use of particulate filters and concerns raised by the WHO about the nitrogen oxides emissions of diesel engines.
The issue is that whilst catalytic convertors work with petrol engines at reducing NOx in exhaust fumes, it does not work for diesel engines.
This led to the development of Euro 6 Diesel in 2014 which cut down the allowed levels of NOx and tackle pollution issues around major UK cities. It also mandated the use of a diesel exhaust fluid for roadgoing vehicles, which needs to be refilled and is the subject of AdBlue removal in construction and agricultural machines.
However, the situation concerning diesel emissions became significantly direr with the Dieselgate revelations in 2015.
What the US Environmental Protection Agency had found is that Volkswagen had designed their cars to only reduce emissions when being tested in laboratories and in fact emitted as much as 40 times the level of NOx when driven normally.
This was in defiance of much of their marketing, which claimed that their engines were far cleaner than regulatory requirements and qualified for a range of green subsidies and tax exemptions.
Since then, there has been increased scrutiny on all combustion engines and the development of the World harmonised Light-duty vehicles Test Procedure (WLTP).