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Diesel was created. Now it has evolved

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The Evolution of Diesel Engines From Dirty and Noisy to Efficient Powerhouses of Today

The journey of the diesel engine began in 1893 when it was developed by Rudolph Diesel.
It is based on the simple principle that air gets hot (very hot!)  when compressed.
When fuel is mixed with this highly compressed air, it  ignites – no need for an  ignition spark!
But its use as an automobile engine was demonstrated in the 1930s by Cummins when he installed a diesel engine in a Packard Limousine.
Diesel engines may have always been fuel efficient and a lot more powerful as far as torque is concerned.
But they generally didn’t find favour with the public, mainly because of their noise and the dirty, smelly smoke.
The smell was because of sulphur and now that ultra low sulphur diesel has become available, the smell is no longer an issue.
But getting rid of diesel noise was not that simple. Basically the noise is caused by the sudden combustion of fuel at high pressures.
Earlier, diesel was injected indirectly by nozzles into a pre combustion area which unfortunately also allowed heat loss.
But now all diesel engines have direct injection where  fuel is injected right into the cylinder (cutting out the need for a pre-combustion chamber)

Previously diesel engines were fitted with rotary diesel injectors that supplied atomized fuel but at low pressures.
As it was mechanically controlled exact precision corresponding to speed change or other requirements was not possible.
This meant that there was inadequate combustion of fuel and higher emissions.

But it was the introduction of turbocharging that helped to achieve greater fuel efficiency and torque at a wider range of speeds than was possible with diesel engines before.
One of the biggest drawbacks of diesel had been a slower pick-up and performance which was totally changed by turbo diesels..

The development of ECU where injection timing, quantity of fuel that is being injected are all controlled electronically were again a major step forward in making diesel engines much more efficient.

However, the situation changed dramatically when the common rail was developed.
The common rail stores fuel in the accumulator rail at a constant high pressure independent of the engine’s speed.
Fuel is injected at precise intervals according to the engine control unit that sends out instructions according to the feedback it gets from the various sensors. These sensors give valuable information regarding speed, temperature, coolant and so on.
As this permits much more exact timing of fuel injection and that too at the high pressures required to atomize it, the knocking and the vibrations so characteristic of diesel are reduced.
It also staggers the release of fuel into several short sprays that helps to reduce the noise.

But though this took care of the noise aspect, it was not enough as one of the biggest drawbacks of diesel has been its exhaust.
Rising awareness of the harmful effects of diesel exhaust on both the environment and human health led to considerable research on emission control.
This has been largely taken care of through EGR, catalytic convertors and DPF.
A major concern are the oxides of nitrogen that tend to form when diesel burns at high temperatures.
The introduction of EGR or the exhaust gas recirculation system ensures that exhaust is mixed with intake air. This reduces the level of oxygen in the air which results in lower combustion temperatures, thereby reducing the oxides of nitrogen.
But hydrocarbons and carbon monoxide are taken care of by catalytic convertors that change them to water and carbon dioxide.
The most harmful part of diesel exhaust has been particulate matter or soot that is now filtered by the DPF or diesel particulate filter.

So over the years, diesel engine manufacturers have responded to the needs of the time and attempted to make these engines more efficient and clean.

 


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