Mods - feel free to move to the Technical forum if you wish, but to me this was more a Discussion item.
In simple terms, add some electronic gubbins, whack up the turbo boost, wind up the fuel injection pressure to some giddy value, and hey presto you have a high performance diesel that'll tow the QE2 from 30-70 in no time flat, stay there all day, and use an egg cup of fuel in the process. Or so it seems.
Given the higher calorific value, how come technology hasn't been applied to petrol engines that have a zillion horsepower, collossol torque, low thermal losses, and run on half an egg cup of fuel per day?
Sure, Mistubishi, Audi, and others seem to now dabble with high pressure direct injection, and we're starting to read about it with turbo engines too, but I can't see how a fuel, diesel, with low calorific value, can use those calories to vastly more efficient effect. Okay, petrol engines lose more energy to heat (why?), but diesels must lose twice this to noise (which also has to come from energy)!
Of course I'm being intentionally simple and a little TIC about this, but still would like to read other's opinions on what is in the pipeline for petrol engines, and whether we will see equivalent huge gains in the near future as for diesels in the past few years.
What triggered this post?
Two things.
Firstly, I still much prefer my V70 2.4T to my brother's V70 D5, especially the far greater refinement under high load, but admit to being mightily impressed by the fuel economy he gets (45mpg v 27mpg) for 90% of the performance I have.
Secondly, watching a brand new, obligatory garish yellow, Ibiza (PD160, I guess) diesel give an Impreza Turbo a very hard time indeed in a dual carriageway drag race! I'm convinced that the result ended the way it did simply because the Ibiza driver saw sense before the Impreza driver, and backed off markedly.
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If you work out the fuel consumption of, for instance, big Mercedes and BMW petrol engines that are housed in luxurious vehicles and compared such consumption with that of small engines in small/medium cars, you'll realise that the Merc and BMW engines are far more efficient ratio wise than their smaller cousins.
Moreover, a Mercedes CDI320 is only half-a-second down on the 0-60mph sprint than its petrol equivalent and does at least 50 per cent more to the gallon.
The only time you really know it's a diesel engine in this case is at reset when there is slight vibration - but most people don't even notice it.
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The much higher compression ratios of diesel engines is one reason why they (typically) convert 45% potential energy of the fuel into usable energy. Petrols by comparison waste about 80%! One reason why petrol engined cars are much warmer in winter after one mile driving.
This is pretty much the reason for fuel savings.
Secondly, it was only about 20 years ago that TDI engines began to be really developed, to the point that performance is no longer a real issue when choosing between the two variants.
I suspect that in five years' time the 'noise' issue will also much less noticeable. Have you heard the new Honda diesel engine?
Imagine Honda even considering such a thing 20 years ago.
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Well, this years Le Mans 24 hour race included a diesel car, the Judd/Caterpillar V10. It retired from the race - whether it was an engine problem or something else I don't know.
However, the Judd wasn't the first - a diesel car was entered in the 1951 Le mans, and that also failed to finish.
I wonder which of Ferrari, Aston Martin or Lamborghini will be first to produce a diesel supercar! A crazy question? Nope - we already have diesel BMWs, Jaguars and Alfa Romeos!
Cheers, Sofa Spud
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In a word turbocharging.
Am I right--diesel burns petrol explodes
Thats why petrol engines can rev higher and why diesels give more torque.
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No you're wrong theyboth burn. If petrol explodes its known as pinking or detonantion and will destroy the engine.
Diesel technolgy has moved hugely since the advent of electronic management of diesels and also common rail injection.
Jim
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Thanks to the second law of thermodynamics, the maximum amount of energy that can be gained from an engine is related to the ratio between the maximum and minimum temperature during the power stroke. Because diesel engines have a greater compression ratio, the gas burned has more room to expand and cool. Thus, because its exhaust is cooler, it can be more efficient (you can get more of the energy out of the system).
If you try to take petrol engines to the compression ratios of a diesel in a search for thermal efficiency, the fuel ceases to burn and starts to explode (knock, above). Because it can't go to the same compression ratio, a petrol engine can never be as efficient as a diesel, even if petrol does have a slightly higher calorific value.
I don't know where petrol engines will go in the future, though I do believe that one of the Japanese car companies has used high pressure direct injection to get down to 1:80 fuel air mixtures (IIRC). The injection is designed to leave a much richer mixture round the spark plug, and almost air elsewhere. The efficiencies are significant, as are the complexities.
V
PS. Second law of thermodynamics explained at:
hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw....1
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PS. Second law of thermodynamics explained at: hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw....1
I preferred the Flanders and Swann version. Transcript at physics.about.com/cs/jokeoftheweek/a/flandersandsw...m .
(Promptly disappears in a cloud of irrelevance.)
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In a word turbocharging.
But turbos have been around for decades on diesels. Midland Red fitted them to some of their home-made motorway coaches (complete with home-made engines)in the 50's. Volvo and Scania trucks have used them since at least the 60's. Why did it take so long for direct injection, intercooled turbo-diesels to find their way into cars? Noise? Cost? Public perception?
cheers, Sofa Spud
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I would think that in the days when only commercial vehicles used diesel engines the incentive for manufacturers to refine and develop the engine wasn't there to anywhere near the extent it is now. Private buyers want a much higher level of sophistication from an engine than a commercial operator and with the massive growth in diesel use (50% of all new cars on the continent, apparantly) the rewards of getting it right are huge.
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Cars using turbocharged diesel engines have been around for a long time - the Peugeot/Citroen variants, for instance, have been hugely popular for many years and have been constantly refined and upgraded.
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The car companies get a huge proportion of their sales from the company-car market. So when legislation is produced that gives diesel company-car drivers a tax break (in comparison to petrol) then demand will increase and the car companies will pick up on that.
In the past, if a punter has wanted a sporty car then petrol has seemed the only option. Car companies may have had the technology for decades to produce diesel engines as good as we get today, but they wouldn't have been economically viable as the customers would have still wanted petrol. But give Joe Public a good reason to choose a diesel, like a tax break for example, and he will suddenly want one, and the sportier the better. If the demand is there for a sporty diesel then it's the last company to develop one who will lose out.
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My son's Ford Focus Zetec 1.8 TDCI's in-gear performance delivers many a mile of exilerating fun, combined with great ride and handling.
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All this technical stuff is fascinating although some of it whizzes a bit over my head.
If oil were an infinite resource, pollution not an issue and the cost of fuel around 25 pence per litre, I'd be quite happy to drive a high performance petrol engined car - though I'd be less than happy at having to rev the knickers off it to achieve that performance - it makes me wince to hear engines turning over at 5000 rpm plus.
As it is, every time I commute at 80 mph on the motorway, at an unstressed 2100 rpm in sixth gear yet with plenty of torquey reserve in hand, and the trip computer telling me I'm averaging over 50 mpg, I bless the day I bought my Ibiza 130 Tdi.
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I have in my posession a copy of "The Motor" annual for 1947, among other pearls of wisdom (like disc brakes never catching on for the normal motorist) they review why Compression Ignition engines would be unsuitable for the average car.
In those days it was because of the need to mechanically measure the droplets of fuel(much easier for large Bus/Truck engines) using a mechanical valve mechanism. Although time has moved on I suspect that the real break in massive increases in diesel power comes straight from the exponential growth in embedded computing power e.g. the average car ECU is now far more powerful than a 1960's mainframe computer.
Simmybear
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