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PDR
751891.  Thu Oct 14, 2010 7:32 am Reply with quote

Hmmm...

The Scotch Yoke prinicple has many basic engineering problems which mitigate against it being successful in anything but very low power applications. The primary problems are bearing wear and vibration. Any implementation requires large counterweights to reduce vibration to acceptable levels, and the interaction between these counterweights and the piston assemblies produces huge cyclic (fatigue-inducing) stresses that require these items to be massively over-sized to ensure acceptable component lives as well as making the resulting engine both large and heavy. The bearing configuration of the pure scotch yoke concept makes for concentrated bearing loads that are difficult to lubricate, and I don't know of any engineering solution to this problem.

The Toyota (and Fiat, and BMW) implementations of the principle (more of a "slider" engine than a true scotch yoke) use convoluted design to revert to rotary bearings, and the linear/rotary conversion is larger than the rest of the engine. It also reintroduces most of the engineering features of the crank-based engine which the concept is supposed to eliminate. Practical trials have shown that the claimed benefits in terms of true sinusoidal motion actually upset the burn characteristics (giving poor emissions performance), and the reduction in secondary vibration s a very small benefit for the trouble taken to achieve it.

I personally feel that this is a technological dead end, like the saltzman engine (which is itself a diaphragmless rocking-piston concept), which have too many detailed engineering problems to be practicable. YMMV.

PDR

 
PDR
751892.  Thu Oct 14, 2010 7:33 am Reply with quote

...and on a point of order:

Unless I'm missing something rockets of any kind are classified as "external" combustion, because the combustion does not take place inside a closed volume.

PDR

 
Alfred E Neuman
751987.  Thu Oct 14, 2010 4:53 pm Reply with quote

I was wondering about the 'correctness' of an internal combustion rocket engine myself...

 
brunel
752079.  Fri Oct 15, 2010 5:51 am Reply with quote

As you say, PDR, although there have been no shortage of proposed alternatives to the current design (such as the aforementioned scotch yoke engine), all too often, the new designs are just as problematic, if not more so, then the design they intend on replacing.
In some ways, it is remarkable that, despite around a century of experimentation, we are still relying on the same fundamental method of locomotion that was used by early pioneers like Karl Benz.

The only unconventional design which has made any headway at all has been the Wankel engine, and even there, although many major manufacturers looked at them (including Mercedes and General Motors), only Mazda has really managed to make any progress with Wankel engines, and produce them on a large scale. Those in their own right are interesting, although yet to gain really widespread acceptance, mainly due to problems in older models with high oil and fuel consumption.

 
plinkplonk
754385.  Sat Oct 23, 2010 4:12 pm Reply with quote

plinkplonk wrote:
Apparently the parts for the internal combustion engine were lain down in 1206, when Al-Jazari described a reprociating piston pump with a crank-connecting mechanism. In fact the Chinese, Mongols and Arabs all used rocket propelled internal combusition engine. The Palace of Versailles had its water delivered by gunpowder powered internal combusition engines. The actual turbine was invented in 1791.

The re-invention of the internal combustion goes on and on. The latest innovation is the scotch yoke engine created by Toyota in 2004. (it turns linear motion to rotational motion and vice versa).


Well Al-Jazari is a source of course, but you could also look at http://muslimmedianetwork.com/mmn/?p=2710 for this. http://muslimmedianetwork.com/mmn/?p=2710 features info about rocket propulsion. http://en.wikibooks.org/wiki/Automotive_Systems mentions the Palace of Versailles. http://inventors.about.com/library/inventors/blenginegasturbine.htm is about the invention of turbine. I think the scotch yolk engine is mentioned later. Did I really get this from so many sources? It seems unlikely...

 
Ion Zone
754393.  Sat Oct 23, 2010 4:55 pm Reply with quote

Jet turbines are feasible, they are supposedly more reliable as they contain far fewer components (as much as four fifths less).

1963 Chrysler Turbine



There is a new concept car using this type of engine. It runs on bio-diesel.

 
AlmondFacialBar
754400.  Sat Oct 23, 2010 5:13 pm Reply with quote

brunel wrote:
PDR wrote:
brunel wrote:
Also, to address this point - I agree that KERS systems do have considerable potential for the future, although at the moment, the F1 systems are on hold due to the high cost of development.


I don't know that that's true - although still legal the KERS weren't used this season for a number of political reasons, but they are back next season with a vengence (that is to say that next season's KERS are allowed longer durations than the 2009 season ones). Many teams will be using them.

PDR

They are thinking of bringing back KERS, but the price for a KERS system is intended on being capped (there is talk of 1.5 million per year for a standard system, based on the Magnetti Marelli system used in 2009, as used by Ferrari and Renault). On top of that, from 2011 onwards, the teams have agreed to limit the number of personnel, including engines and powertrain development staff, which will slow down the development of KERS systems quite a bit, I would wager.

So, although we could well see KERS back in the sport, the amount of development work allowed on the current KERS system is going to be quite limited, to prevent a repeat of the spending war last time (there was talk that Mercedes spent as much as $80 million in joint research with Zytek).

Anyway, I'll answer the earlier question about the BMW turbo engine, and what fuel it used.

There is an urban legend that BMW used a secret WW2 aviation fuel, or rocket fuel, which stopped the fuel igniting prematurely - spread, in part, by a former employee.
It also seemed to gain a lot of popularity because the official fuel supplier to BMW had been part of IG Farben during WW2, and had done a lot of research into aromatic chemicals derived from coal, some of which had gone into various fuels used by the German military at the time.

However, there are a lot of problems with this story - WW2 aviation fuel typically had a RON of 110-120, but, in F1, the RON value was limited to 102 (and the Brabham BMW team were nearly disqualified when it was found that they were very close to the limit in 1983). Secondly, aviation fuels of the time had a high alcohol content - also banned in F1 at the time.

The true answer, based on testimony from a former Wintershall employee (BASF and Wintershall, in a combined project, supplied BMW with the fuel for their engines) appears to be toluene and heptane.

Toluene has a high energy density, which was very important, because the rules at the time banned refuelling (from 1983 until 1993), and restricted the fuel tanks of the cars.
More important was toluene's high resistance to premature ignition - which was vital, especially for the qualifying engines, which worked at very extreme pressures and temperatures. To make sure that the fuel would just sit below the limit of RON as 102, a small amount of heptane would be blended into the mixture.

So, the correct answer would be about 85% toluene, and 15% heptane, with possibly traces of other aromatic chemicals - but certainly not, despite the ring that the story has to it, a Nazi rocket fuel.


Also, using fuel from coal hydration wouldn't really have worked from a cost/ benefit point of view because the fuel isn't as good as it is expensive to produce. The only capitalist country that has used the technology on an industrial basis since 1945 was apartheid South Africa because owing to the sanctions they had far more coal than oil. I guess you could say it's a bit of an emergency technology. Currently the only countries that use it beyond research purposes are China and Mongolia.

:-)

AlmondFacialBar

 
PDR
754446.  Sun Oct 24, 2010 3:35 am Reply with quote

...or even the Rover gas turbine, but they are hideaously inefficient because turbines are lousay at running at anything much below full power. A turbo-electric system might be worthwhile, combined with a large KERS, but the manufacturing costs would be high.

It's also true to say that although the component cound of a turbine is lower than a piston engine, the actual components are more highly stressed (to be efficient the 1st stage HP turbine blades will be operating in an environment that is 20-30% above their melting point) and so the reliability benefit can be moot.

PDR

 
Alfred E Neuman
754461.  Sun Oct 24, 2010 5:15 am Reply with quote

AlmondFacialBar wrote:
Also, using fuel from coal hydration wouldn't really have worked from a cost/ benefit point of view because the fuel isn't as good as it is expensive to produce. The only capitalist country that has used the technology on an industrial basis since 1945 was apartheid South Africa because owing to the sanctions they had far more coal than oil. I guess you could say it's a bit of an emergency technology. Currently the only countries that use it beyond research purposes are China and Mongolia.

:-)

AlmondFacialBar


That's not strictly true, although the Sasol plants were developed for exactly the reasons AFB mentioned, they are still being used to this day, and contribute a significant percentage of South Africa's fuel demand (somewhere between 25 and 40 percent).

 
brunel
754483.  Sun Oct 24, 2010 5:49 am Reply with quote

PDR wrote:
...or even the Rover gas turbine, but they are hideaously inefficient because turbines are lousay at running at anything much below full power. A turbo-electric system might be worthwhile, combined with a large KERS, but the manufacturing costs would be high.

It's also true to say that although the component cound of a turbine is lower than a piston engine, the actual components are more highly stressed (to be efficient the 1st stage HP turbine blades will be operating in an environment that is 20-30% above their melting point) and so the reliability benefit can be moot.

PDR

There have been a few concept cars which have used a micro turbine to power a generator - Jaguar showed off one recently at the Paris Motor Show, called the CX-75. http://www.topgear.com/uk/car-news/paris-motor-show-2010-jaguar-cx75-supercar

Admittedly, it is unlikely that this will be built for some time, although the turbine engines fitted to that car are in commercial production (and were originally designed for motorbikes - the designer wanted to race a bike at the Isle of Man TT powered by one of these micro turbines).

 
AlmondFacialBar
754562.  Sun Oct 24, 2010 8:45 am Reply with quote

Alfred E Neuman wrote:
AlmondFacialBar wrote:
Also, using fuel from coal hydration wouldn't really have worked from a cost/ benefit point of view because the fuel isn't as good as it is expensive to produce. The only capitalist country that has used the technology on an industrial basis since 1945 was apartheid South Africa because owing to the sanctions they had far more coal than oil. I guess you could say it's a bit of an emergency technology. Currently the only countries that use it beyond research purposes are China and Mongolia.

:-)

AlmondFacialBar


That's not strictly true, although the Sasol plants were developed for exactly the reasons AFB mentioned, they are still being used to this day, and contribute a significant percentage of South Africa's fuel demand (somewhere between 25 and 40 percent).


Still coal-based? Even Leuna switched to oil while still in GDR-times, so if SASOL manage to run coal hydration efficiently that's quite some feat.

:-)

AlmondFacialBar

 
Bondee
754602.  Sun Oct 24, 2010 10:48 am Reply with quote

plinkplonk wrote:
I think the scotch yolk engine is mentioned later.


Is that what powers the machine that's used to make scotch eggs?
; )

 
PDR
754607.  Sun Oct 24, 2010 11:01 am Reply with quote

I was wondering when someone would spot that. I'm waisted here...

PDR

 
Bondee
754617.  Sun Oct 24, 2010 11:13 am Reply with quote

PDR wrote:
I'm waisted here...


I wouldn't say that. We think you're quite hip.

 
deadstick
769778.  Sat Dec 25, 2010 10:24 pm Reply with quote

Re "internal combustion", it is quite appropriate to call a rocket that. The combustion does indeed take place inside the engine, and more important, in the working fluid -- in fact, it generates the working fluid. Any combustion that takes place outside the rocket represents energy gone to waste.

Remember, "flame" and "combustion" are not the same thing. A flame is a region of space that contains a gas at a high enough temperature to be ionized. The flame behind a rocket has substantially completed its combustion before it ever leaves the nozzle.

Re "jet turbine", it is not appropriate to apply that to the Chrysler turbine car. It has a gas turbine engine. In the turboprop engines used in aircraft, most of the energy developed by the turbine is converted into shaft work which powers a propeller and the remainder is accelerated through a nozzle to create a "Newton's third law" force, or jet propulsion, which accounts for perhaps a quarter of the total thrust. In the Chrysler engine, almost all of the turbine energy goes into shaft work and the remainder is dissipated in a muffler -- no jet thrust takes place.

rj

 

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