Some calculations

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16-12-2007, 07:07 AM
mikinoz

Quote:

Originally Posted by Big Al the Butchers' Pal

As for the comments re the Golf 1.6, as far as I am concerned it is a better car than the Toyota Corolla, albeit with a less powerful engine.

I have to say the 1.6 MKV that I drove was reasonable and a huge advancement over the 1.6 MKIV in standard form! :cool: My company car is a corolla and they are 2 different beasts indeed!
16-12-2007, 12:27 PM
GermanwithaVdub

can someone confirm what im about to infer.

i dont have much experience with an mkv fsi, but im guessing that if you're a person who constantly revs close to redline and always hard acceleration, that you're going to use exponentially more fuel than if you drive the same way in the equivalent diesel?
16-12-2007, 01:18 PM
Big Al the Butchers' Pal

Quote:

Originally Posted by GermanwithaVdub

can someone confirm what im about to infer.

i dont have much experience with an mkv fsi, but im guessing that if you're a person who constantly revs close to redline and always hard acceleration, that you're going to use exponentially more fuel than if you drive the same way in the equivalent diesel?

You are correct. The efficiency of an internal combustion engine is proportional to the compression ratio. A diesel engine has far greater compression (11 to 1 vs 19 to 1), and is thus more efficient. The cost of this efficiency is however higher engine drag torque. This is the case because the internal moving and reciprocating parts are heavier and also because more work needs to be done to achieve the higher compression. The engines are also heavier. The 2.0 TDI engine is 140kg heavier than a 1.6 petrol engine. A TDI engine also needs to use 20% of engine output to drive the turbocharger via the exhaust stroke.

Diesel engines are therefore around 30% more efficient in producing power. This is why diesel engines are used exclusively for power applications such as generators, compressors, ships, pumps and trucks. Diesel engines are however less efficient that petrol engines in NOT producing power, because the drag torque is double that of a petrol engine.

So for aero applications and motor vehicles, where the engine spends the majority of the time at part load, the petrol engine will be more efficient in non full load situations. This is why I get over 900 km from a tank of fuel in my car, because I spend most of the time cruising on the highway at 80 to 100k/h at a 10 to 20% of full load application.

If I were however to go on the autobahn at 180km/h flat pedal, my car would drink like an Irish sailor. The diesel engine would be far more efficient in such a constant full load situation.

If you are a lead foot then the diesel will be a better choice, however driven ultra efficient, the petrol engine will be (in overall terms) more efficient than an equivalent diesel engine. This example was proved in the recent fuel consumption world record where a petrol VW Golf achieved that record.
16-12-2007, 01:22 PM
Big Al the Butchers' Pal

Quote:

Originally Posted by TDI Dude

Well gentlemen I'll just say one thing on this subject.... YOU BUY A DIESEL AS A CHOICE NOT BECAUSE THE ACCOUNTANT SAID SO!!!! P.S. cant wait for mine to turn up!!!!!! :D

You are correct in your analogy. I buy Benson & Hedges as a choice, not because my doctor said so.
16-12-2007, 01:34 PM
GermanwithaVdub

Quote:

Originally Posted by Big Al the Butchers' Pal

You are correct. The efficiency of an internal combustion engine is proportional to the compression ratio. A diesel engine has far greater compression (11 to 1 vs 19 to 1), and is thus more efficient. The cost of this efficiency is however higher engine drag torque. This is the case because the internal moving and reciprocating parts are heavier and also because more work needs to be done to achieve the higher compression. The engines are also heavier. The 2.0 TDI engine is 140kg heavier than a 1.6 petrol engine. A TDI engine also needs to use 20% of engine output to drive the turbocharger via the exhaust stroke.

Diesel engines are therefore around 30% more efficient in producing power. This is why diesel engines are used exclusively for power applications such as generators, compressors, ships, pumps and trucks. Diesel engines are however less efficient that petrol engines in NOT producing power, because the drag torque is double that of a petrol engine.

So for aero applications and motor vehicles, where the engine spends the majority of the time at part load, the petrol engine will be more efficient in non full load situations. This is why I get over 900 km from a tank of fuel in my car, because I spend most of the time cruising on the highway at 80 to 100k/h at a 10 to 20% of full load application.

If I were however to go on the autobahn at 180km/h flat pedal, my car would drink like an Irish sailor. The diesel engine would be far more efficient in such a constant full load situation.

If you are a lead foot then the diesel will be a better choice, however driven ultra efficient, the petrol engine will be (in overall terms) more efficient than an equivalent diesel engine. This example was proved in the recent fuel consumption world record where a petrol VW Golf achieved that record.

ah thanks for that, very clear now :)
16-12-2007, 06:16 PM
neil

Quote:

Originally Posted by brackie

You'd need to chuck resale value into the mix. Generally this is higher on a diesel than on a petrol.

Servicing the diesel may also be slightly more expensive as (if you love your engine) you'd need to change your fuel filter more regularly than recommended, and I'd like to know the cost comparison between the cambelt service for the two engines.

Fuel costs vary greatly depending on global supply and demand. At present heavy supply of diesel fuel to Asia is pushing the price up. This was not the case 30 years ago when diesel was up to 10c cheaper per litre than petrol. Who knows how this will change in the near future :???:

Driving technique can affect fuel consumption enormously. According to the computer I got 4.9L/100km on a trip to Launceston (300km) last Friday. This included 110kph on much of the Bass hwy, and also a lot of running around town, whereas 2 weeks ago it was 5.1 on a trip to Hobart when I was a little more "enthusiastic" in my technique :)

I won't go into why I love diesels, 'cos it's a personal thing.

Hey brackie.
Good to see you still around.
Have missed your posts re: fuel consumptions.

Did a trip from Sydney to Young via Boorowa approx 380km @ 4.7 L/100
Return trip, took it easier via Wombat 350 km @ 4.1 L/100:D
Was sitting on 4.0 until I hit the city.
Anyway how do these manufactures get the figures they state on the
brochure. I cant get anywhere near there estimate of 6.1 even in the city.
Take care Neil.
16-12-2007, 06:24 PM
evorobin

Quote:

Originally Posted by Big Al the Butchers' Pal

You need to do the calculations for Golf 1.6 Petrol vs Diesel

This car runs on stock unleaded. According to my calculations

$2500 extra costs me 13% lost investment income in my share fund per annum = $325 per year.

Extra fuel consumption is 2 litres per 100km.

So, to even start paying off the $2500 cost, I have to save more than $325 per year in fuel.

You forgot to factor lost opportunity cost of the extra cost.

Also the fuel cost is now 15 cents cheaper for a 1.6 petrol vs diesel.

This equates to a 0.8 litre per 100km equivalent fuel saving at current prices.

Half of the saving in consumption is blown in extra fuel cost.

Even if I travel 20,000 km per year, I am still behind in cash terms and the $2500 outlay will never be paid off, no matter how long I keep the car.

Then you have the issues with dual mass flywheels that cost major dollars every few years etc.

And PRAY you never need to do major engine repairs on a diesel engine, as that is mega dollars.

And Pray you never get a shonky (added kero + heating oil) load of diesel or water in the fuel, as that will totally stuff your engine and require a full engine rebuild.

ABRZ from vortex australia has entered the building LOL
16-12-2007, 06:25 PM
Spoddy

Quote:

Originally Posted by neil

Anyway how do these manufactures get the figures they state on the
brochure. I cant get anywhere near there estimate of 6.1 even in the city.
Take care Neil.

We seem to have found the method.... short trips to the station where the car doesn't warm up :( Seems such a waste driving a car that way but then its my wife's car and thats the only way to get to work. We are averaging 6.8 whilst the silly MFD says 5.9 to 6.1.
16-12-2007, 07:02 PM
neil

Quote:

Originally Posted by Spoddy

We seem to have found the method.... short trips to the station where the car doesn't warm up :( Seems such a waste driving a car that way but then its my wife's car and thats the only way to get to work. We are averaging 6.8 whilst the silly MFD says 5.9 to 6.1.

Interesting spoddy.

I'm quoting the MFD, I'll do a few manual calculations and see what
I come up with.
neil.
16-12-2007, 07:05 PM
GermanwithaVdub

Quote:

Originally Posted by neil

Hey brackie.
Good to see you still around.
Have missed your posts re: fuel consumptions.

Did a trip from Sydney to Young via Boorowa approx 380km @ 4.7 L/100
Return trip, took it easier via Wombat 350 km @ 4.1 L/100:D
Was sitting on 4.0 until I hit the city.
Anyway how do these manufactures get the figures they state on the
brochure. I cant get anywhere near there estimate of 6.1 even in the city.
Take care Neil.

you must drive VERY conservatively. i was lucky to get 6.1 or below on my 2.0tdi comfortline when i had it. mostly up around 7 or 7.5. and you cant count the cruising on a highway, i can make my car sit at 3 point something on a straight flat stretch, it has to be a mix of city/highway to have relevance.

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