Wednesday, 27 February 2013

Talk : The future of Diesel's Engine

A recent talk at Nottingham Café Scientifique was presented by Prof Richard Stobart entitled “What is the Future for Diesel’s Engine?”

To begin with, Prof Stobart pointed out the key point that a mid-sized diesel engine (such as used in construction equipment) might cost £40k to buy - but would use about 24 times this value in fuel over its lifetime.

The Prof then moved on to give an outline of the broad range of diesel engines that are available:

The range of diesel engines available

Perhaps the first example of attempts to make internal combustion engines can be found in 13th century Chinas’ invention of rockets.

This was followed in the 17th century by Christian Huygen’s designs for a basic form of internal combustion engine (powered by gunpowder) which was developed by his partner Denis Papin.
Huygens was ahead of his time in many ways, not least in adopting the tight perm hairstyle that would not become widespread until the 1970s

Work in such “gunpowder engines” then ceased as steam powered “atmospheric engines” were developed and began to succeed commercially Steam engines ruled for over a hundred years, until the brilliant French military engineer and physicist Sadi Carnot undertook a serious study of the science behind combustion (published as “Reflections on the Motive Power of Fire) in 1824. The most important part of this wide-ranging work was the presentation of what is now knows as the “Carnot Cycle”
An ideal Carnot Cycle

1 to 2 : 300K Heat applied and applied pressure reduced - gas expands and takes in heat to maintain constant temp

2 to 3 : Heat source removed and applied pressure further reduced - gas expands and cools

3 to 4 : 200K heat applied and applied pressure increased - gas is squeezed and gives out heat to maintain constant temp

4 to 1 : Heat source removed and applied pressure increased - gas contracts and heats

Work performed is the area bounded by 1-2-3-4

Although Diesel patented his concept (see here), the wording of the claims meant that his patent could be challenged and this prevented him from obtaining the level of royalties he might otherwise have been able to obtain.

Diesel died in 1913, seemingly by committing suicide by jumping from a steamer travelling to London.

Diesel's original engine

Other noteworthy events in the development of the diesel engine were..

1905 : Alfred Buchi obtains a patent for turbocharging

1920’s : Sir Harry Ricardo develops many improvements to engine design

1930 : Junkers Jumo lightweight horizontally opposed engine

1932 : Citroen Rosalie - the first production diesel car.

1946 : Compact, powerful Napier Deltic Engine

1980s : The arrival of electronics

1997 : First automotive application of the Common Rail Fuel System (initially developed by Fiat who sold the technology to Bosch.

2000’s : Increasingly strict Emissions regulations

Prof Stobart then considered how the efficiency of the diesel engine might be improved to 50%.

One way of considering where improvements can be made is to consider the thermodynamics of the Otto cycle and investigate areas where current engines do not follow the cycle optimally.

For example, energy is lost in diesel engines as exhaust heat and friction, attempts can be made to recover these with waste heat recovery systems and by using electrical rather than mechanical power for engine subsystems

Another area where research may be of value is to consider how a larger volume of air can the introduced into the engine. This may seem like a trivial issue to address, but is actually very difficult as there is not a lot of time for the air to enter the cyclinder.

Finally, Prof Stobart mentioned a technique that his group was using to quickly undertake research - using virtual systems modelling to fool an engine into thinking that, say, an exhaust heat recovery system has been added, to see how the engine behaves in response.

The question and answer session, much longer than the actual talk, is one of the best features of Cafe Sci - and is often a source of much interesting information in its own right.

In this case, the Q&A included the following little nuggets of information...

Petrol and Diesel have a very high energy density, and filling a 40litre car tank (which takes around 60 seconds) represents an energy transfer rate of some 24,000 kW. To get an idea of just how high a density this is, compare it to a typical electric vehicle charging station, which charges at about 6kW. And a kilogram of diesel contains the same amount of energy as 20-40kg of battery. On the othe rhand, the efficiency of an electric motor is much higher than a diesel engine (90% comapred to ~35%) and is further boosted by technologies such as regenerative braking.

One reason that there is so much pollution in China is that the refineries there often buy cheaper "sour" oil that is high in sulphur, and then do not fully remove this contaminant during distillation (see 2004 article here)

Prof Stobarts team is part of the TEG energy recovery group .

Image Sources
Huygens, Engine