The rises and falls of diesel engines
Tuesday, 26 June 2018
Three years ago, Volkswagen's clean fuel claim for their diesel engines was destroyed by 'Dieselgate', a scandal brought to light by the car emission testing authorities in California.
They discovered that when Volkswagen's turbocharged direct injection diesel engines were operating under normal road conditions, the exhaust emissions were up to 40 times the allowable limits.
In modern cars, computers manage the engine performance and it was revealed that Volkswagen engineers had programmed these computers to activate the emissions controls only during laboratory emissions testing.
According to Reuters newsagency, the scandal has cost Volkswagen US$30 billion in total.
**READ MORE
* German automakers under fire over diesel exhaust tests on monkeys
* VW emissions scandal: How it unfolded
* How VW has changed since the emissions scandal - and how it hasn't
* VW boss imprisoned over scandal**
Diesel engines have an interesting history.
The Industrial Revolution was powered by steam engines – these are external combustion engines, meaning the fuel, usually coal, burns separately from the workings of the engine.
This is very inefficient because only a fraction of the heat generated by the coal drives the engine; the rest is dissipated during heating of the boiler.
Worse still, steam engines are bulky, take a long time to generate the steam from a cold start and are labour intensive.
Engine designers realised it would be far more efficient if the combustion could be done inside the engine – this was called an internal combustion engine.
German engineer Rudolf Diesel, noticed that if fuel oil was placed inside a piston cylinder and the plunger pushed hard, the increase in pressure inside the cylinder would heat the air enough for the fuel to ignite.
In 1892 Diesel patented his compression-ignition engine.
Its efficiency was 30 per cent, three times more efficient than its steam counterpart - but there was a problem.
A rival engine was being developed and tested.
Like the diesel engine it was an internal combustion engine, but it used a more volatile fuel - petrol.
Diesel is difficult to burn in the open but petrol burns immediately and violently.
In a petrol engine the fuel air mixture is ignited with electrically produced sparks from a spark plug.
The spark-ignition engine produced a more powerful combustion than its compression-ignition rival, but it was only half as efficient.
Nevertheless, petrol engines were light and found a ready market in motor cars whilst the diesel engines remained big and heavy.
But diesel engine designers fought back.
In 1931, Englishman Harry Riccardo patented a small pre-chamber, which he called the comet swirl chamber.
The fuel entered the pre-chamber, burned and exited, rushing into the main combustion chamber where it generated two counter rotating vortices which completed the combustion.
This vigorous mixing of the fuel air mixture and shearing of the flame dramatically improved the performance and economy of the diesel engine.
These robust, economic engines were successfully used in London's buses.
Despite these improvements, diesel engines still didn't have the responsive, powerful operation of their petrol counterparts.
Then, in the 1970s came the Arab oil embargo.
Oil prices rocketed and the race was on to design more efficient engines.
Diesel engine designers found a solution – dispense with the swirl chamber and spray the fuel directly into the main combustion chamber.
This greatly increased the surface area of fuel exposed to the air and enhanced the performance and smoothness of operation of the diesel engine.
It was a winner and with the refinement of turbo-injection, by the 1990s sales of diesel cars exceeded those of petrol cars.
Then in 2015 came Dieselgate.
Tragically, in 1913 the inventor of the original diesel engine, Rudolf Diesel, threw himself off a ferry into the North Sea.
He was rich and widely admired for his ingenious invention – why had he committed suicide?
It is thought that Diesel, a Utopian, was shattered when he saw the widespread use of his engines to power the machines of war.
Despite the current problems, there is no doubt that Rudolf Diesel's invention has improved the quality of life of millions of people by providing modern, economic and reliable versions of diesel engines for use in numerous applications such as trains, ships, and cars.
That said, in a world where emission quality has become the top priority, it remains to be seen if Diesel's invention can overcome the dirty emissions scandal and continue to dominate the car market.