what is diesel?

[gldgti]

back on the pros and cons, and a little on bio diesel

my litle green monster runs on biodiesel most of the time, and loves it too. it'll run a little quieter, smoother and generally a bit nicer, with more low end power too (with a slight decrease at the top end...)

my '79 1.5 4-speed will get about 40mpg at worst, if theres a lot of huffing and puffing around town and running long distances at 100km/h, (like you said, brackie...)

HOWEVER - long distance runs at 90 - 95 km/h will increase your fuel economy by a LOT. its a trait of the gear ratios and the power curves of the 1.5's it seems, as your peak torque is at 3000rpm, and at 90km/h, it'll rev somewhere close to 3150rpm - barely above peak torque. it seems to be the most economical spot to run at, once you get above that, she's really in rev-mode, where you need a lot more fuel for your increased power... just an interesting point.

60mpg is a fairly easy to achieve economy with the 1.5, and though i've never done it myself, i would say 70mpg is possible too, with a 5-speed gearbox and a nicely running engine (an most important, a patient light footed driver)

Brackie - ive always dreamt/hoped/wished for the 5-speed and a turbo engine to drop into the golf...keep us informed on your developments in your exploits.....

and the 0-100 times? never say never. remember that a mk1 gti (the fastest gti to date, stock) had 110hp. a 1.9 turbo will punch out about 95hp standard, and with about double or more torque....need i say more..?

[gldgti]

and for redmk1....

diesel is cetane based fuel, meaning its supposed to be mostly 16 carbons long hydrocarbon chains (where petrol is meant to be moslty octane, 8 carbons long)

instead of using spark ignition, diesels utilise a trait of straight chain alkanes called compression ignition. it is what all petrol loving people dread, and diesels rely on it. instead of igniting the fuel and air with a spark plug at the right time, diesels compress just the air until it is at extreme pressure (far more than is required to ignite the fuel spontaneously) and THEN spray in the fuel where it instantly ignites.

since internal combustion engines all rely on high compression ratios for economical running, diesels have a huge advantage, with typical compression ratio around 20:1 in a diesel, with a petrol engine usually around 10:1

the mk1 1.5 diesel is at the extreme end of this, with 23.5:1 compression ratio, and most vw tdi engines at about 19.5:1 i think.

this high compression means that the overall mechanical efficiency of the engine is greatly increased over that of a petrol engine. this mixed with the more favourable power distribution in a diesel (where the torque and power curves distribute power evenly throughout the rev range instead of bunched up at the top end like in a petrol engine) make it possible to get fantastic fuel economy through good driving and use of the torque down low.

(as an example, my little 50hp golf will pull up steep inclines in 3rd gear at 40km/h without too much real effort. 3rd gear tops out at 105km/h, so you can see that even though the max power is far less than in a petrol car, you get a lot more useful power where it counts - i mean, who wants a 6 speed trannie with all the gears 500 rpm apart to drive around town in? (anyone in a honda, im talking to you!)

[gldgti]

sorry, also meant to say....

i see plenty of mk4 TDI's around, so i think all they missed with the diesels was the 80 - 95ish period....

[imported_brackie]

Excellent technical stuff! Although probably wasted on the petrol heads. Your description of compression ignition, alkanes and cetane numbers takes me back to my diesel fuel injection certificate courses in the Old Country (many years ago!).
Yeah, the broad torque band is the biggest benefit of diesels, and if you drive within it you'll get the best from them. With a 4 speed, anything above 100kph is just blowing diesel down the exhaust pipe, as it doesn't get time to burn completely before the next cycle begins. Not good for the environment or the bank account. The 5 speed (apparently) gets you over the 100kph mark and lets you burn all of the fuel, but by all accounts you have to drop back to 4th on grades.
Oh, yeah... Diesel engines run at about 30 - 33% efficiency, while petrol engines are at about 27% (these days).
And... I've yet to see a '90s Golf diesel in Oz. Please show me one!

[gldgti]

thats an interseting point about the efficiency %'ges. when you say "(today)" do you mean petrol engines today or petrol and diesels today?

just as a point of conversation, i find it annoying that manufacturers like honda and toyota and the media talk up hybrid vehicles so much, with their average consumption of 4.9l/100km etc as being vastly efficient and environment saving blah blah blah, when i've measured my economy to be 5l/100km many times, and my car is 25 years old.

sure you can argue that it blows black smoke and makes lots of NOx's, but thats only if it runs on petro diesel, not bio diesel, which is much much cleaner, AND totally greenhouse neutral.....

oh ohh, im raving.......

sorry this oughta be in another thread, but anyone wanting to know what is diesel i guess should know the whole glorious picture

aydan

[imported_brackie]

And... I've yet to see a '90s Golf diesel in Oz. Please show me one!

Yeah, OK...I've seen it at "Carsales"!

[Golf Loon]

Thats a good point on manufacturers figures. Cars these days are so heavy that engines have to be more powerful to return the same figures. The Golf grew heavier in each incarnation, filled with electronics and plastic and although the engines were more powerful, the weight offset this. thus cars are actually getting slower. A Light car with the later model more powerful engine would be the way to go. How good would your diesel figures be with a 1.9TDi and an 800kg car?

[imported_brackie]

thats an interseting point about the efficiency %'ges. when you say "(today)" do you mean petrol engines today or petrol and diesels today?

Modern petrol engines are more efficient than they were a few decades ago. You'd probably find that some of our members' Mk1s are too as they have been ported, electronic ignitioned etc. Efficiency is measured in power at the flywheel per unit of fuel energy input.

just as a point of conversation, i find it annoying that manufacturers like honda and toyota and the media talk up hybrid vehicles so much, with their average consumption of 4.9l/100km etc as being vastly efficient and environment saving blah blah blah, when i've measured my economy to be 5l/100km many times, and my car is 25 years old.

There you go... More efficient. I wonder what the consumption of a hybrid would be if they had a diesel engine?!

sure you can argue that it blows black smoke and makes lots of NOx's, but thats only if it runs on petro diesel, not bio diesel, which is much much cleaner, AND totally greenhouse neutral.....

Only blows black smoke if it isn't adjusted properly. Sure, more particulates than a petrol or LPG engine, but not if you burn biodiesel...and, Mr Peugeot and Mr VAG are now installing particulate filters on their new cars. As for oxides of nitrogen, diesels produce a lot less than petrol engines. Oh, and they are more thermally efficient so they produce less net heat.

oh ohh, im raving.......

sorry this oughta be in another thread, but anyone wanting to know what is diesel i guess should know the whole glorious picture

Rave away! Turbo diesels have taken over in more enlightened countries. Whether they will here is another story. I think all it would take would be GMH or Ford to bite the bullet and put one in a Commodore or Falcon and opinion would spin around very quickly. But look how long it took them to make LPG cars! Also, if we can produce biodiesel at a price a fair bit cheaper than petrol, people would sit up and take notice.

[gldgti]

a mk1 with a 1.9 td? well, its all the rage among dieselers in the states and a little bit in the us, as its far easier to come by a 1.9td engine over there.

but to answer your question - if i can get 5l/100km in my 50hp 25 year old diesel, in a car that i have had weighed at 840kg, and the tdi guys on forums claim they can get 5l/100km too, in modern golfs which weigh, what, 1100 kg? then the thought of a 1.9 tdi in my car almost makes the few thousand dollars it would cost to make it happen be worth it.

dare i say.... 4l/100km?

Sharkey, a well known forum user at vwdiesel.net, has built a mk1 diesel hybrid. i dont know about consumption figures, but i'd say they are probably nothing short of astounding....

a turbo diesel commodore? maybe, but i wouldnt drive one

[imported_brackie]

Yeah, Mr Sharkey's a member of this forum, too. Very knowledgable gentleman.