O/T - diesel car - "modern" car why extra 30+percent fuel consumption?

Hi all
On this bright morning I thought to ask you here on r.c.m. if any of
you know what makes the difference for a diesel car between very good
fuel consumption and just good fuel consumption.
The punchline is - where is the extra 30+% fuel consumption going in a
"modern" car?
UK / Europe factor - every car mentioned has manual ("stick-shift")
transmission - five-speed or six-speed.
For nine years, I had a car which reached 20 years of age and went
everywhere, every day, at 63MPG (Imperial 10pint gallon (4.536L); 50.4
miles per US Gallon; 22.2km-per-Litre). With plenty of power -
delight to drive. Turbo spun-up and it surged forward no need for
gear changes.
Even a vibrating rattly tiny Fiat supposed to do 70MPG (Imperial) did
only 55MPG.
My current car mid-range (European style - probably very compact by US
standards) is super luxurious, has a six-speed gearbox, goodly amount
of power - no hills steep enough to keep speed below 70MPH when
cleaning out the engine with sustained accelerator to floor - but
"only" 48MPG (38.4miles per US gallon; 17km per Litre)
A few years ago I was told 60+MPG "is a thing of the past" "with new
emission reg.s" (!!).
The 63MPG car, built in late 1990's, was turbo-diesel, fly-by-wire
diesel injection, probably no filters or anything on the exhaust side
of the engine.
At 63MPG, it cannot have been throwing anything /
much out of the
exhaust part-combusted - else it wouldn't be doing 63MPG...
It weighed 1~1/2tonnes - heavy for a smallish compact car.
However, whatever that weight was, it seemed to be involved in
something which nett left you advantaged.
That was 1.9Litres - quite large by UK / Europe standards - where my
more modern car is something like 1.6Litres capacity.
It sounded like a tractor, for sure, when at idle.
That car, the 63MPG car, was Spanish built and badged from the
Volkswagen stable. Someone told me it had the engine from the earlier
VW Golf GTD (turbo diesel performance model). When that was no longer
the new premium model.
So yes, if you could be happy with
a car which sounded like a tractor, you warmed it up slowly to be kind
to the environment, didn't mind that the heaters only worked after
about 3 miles of driving (if you aren't burning much fuel you are not
producing much heat, plus you have a big heavy engine to warm up)
then you got a totally delightful car.
But that fuel consumption... 63MPG (Imperial)
That is the possible.
Where is that extra 30+% fuel going in a "modern" car ???????
The 63MPG (Imperial) shows what is needed to do the job with a
"straight diesel" car. So you can use that as a reference and ask -
for a "modern" car, where is that extra 30+% of "un-accounted-for"
fuel going ???????
I would be very very interested to know.
I've had that question in my mind for since I found I couldn't
like-for-like replace the wonderful VW-family car.
Regards,
Rich Smith
Reply to
Richard Smith
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Rich,
Sounds like I might have the same engine in a slightly newer 1.9 TDI Passat and it's still going and hardly doing any mileage these days so I'm aiming to keep it going as long as possible, last model before DPF introduction. BTW a UK gallon is 8 pints it's the difference in UK and US pint sizes that makes the difference
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Reply to
David Billington
Richard Smith wrote on 5/30/2022 5:57 AM:
I am not a regular in this newsgroup but I once owned a VW Jetta TDI, and I think I am knowledgeable enough on this matter to answer your question.
Diesel fuel has higher "energy density" than regular gasoline (or petroleum in the UK). In the oil distillation process in the oil refinery, diesel fuel is less refined than regular gasoline, and thus contains more complex hydrocarbon molecules than regular gasoline. Theoretical a tank of diesel fuel contains more heat energy than the same volume of regular gasoline if you can burn the fuel thoroughly through proper combustion.
A diesel engine does not use a spark plug to ignite the fuel in each combustion cycle. Instead it uses high compression to ignite the air-diesel mixture, therefore a diesel engine requires stronger metal components, and thus lasts longer and costs more money to build.
Another advantage of using diesel is that diesel is technically equivalent to Jet A1 fuel + motor oil. Jet A1 fuel is a common aircraft engine fuel which is basically a fancy type of kerosene. Because the less-refined diesel fuel has the engine oil built into it, it actually lubricates the combustion chamber in each stroke.
With the combined effect of better metal components in building a diesel engine, a higher energy density of diesel fuel compared to regular gasoline, and the innate lubricating power of diesel fuel itself, a diesel engine is renowned to have better fuel economy and last longer.
The disadvantage of using diesel engine in a car is that a diesel engine is more sluggish in picking up speed compared to a gasoline engine. If you want jack-rabbit starts after each red traffic light, then a diesel car will disappoint you.
Diesel engines are the preferred choice for vehicles that require fuel economy and engine durability. That's why commercial trucks are almost exclusively diesel.
Hope that helps.
Reply to
invalid unparseable
That is mainly "diesel vs petrol/gasoline". It's said - half the gain in fuel consumption comes from a higher thermodynamic efficiency and the other half of the gain comes from more calorific fuel.
I'm thinking when comparing diesels, where does the about 30% excess fuel consumption go in diesel vehicles meeting current "emission regulations". Obviously the crazy thing is, with global warming yes (amazed when realise can see it in how high the tides rise compared to previous) and suspicion our CO2 production could be driving that - why would higher fuel consumption / more CO2 production be desirable? I know diesels operate at such a high pressure and temperature that they do "cook" some of the nitrogen and oxygen together to produce nitrous oxides - but for reduced CO2 production there looks to be a balance here. I suspect the answer is run on electric power in cities and run diesel / fossil-fuel on long runs.
Performance - if you rev-up a diesel and dump the clutch you could if that was your thing squeal the tyres. But for day-to-day driving, the fat smooth power delivery of a turbo-diesel makes for a lovely vehicle to drive especially on our twisting roads. As you will surely well know with the car you mention.
Reply to
Richard Smith
I forgot to mention in my other post but a mate recently raised the issue where he was getting noticeably poorer fuel consumption on current pump diesel than a few years ago. He runs a Nissan SUV, a FIAT camper van and for work a Ford Transit, all diesel and the vehicles haven't changed just he isn't getting the same distance out of a tank as he did a few years back. He mentioned the rumour? that cheap diesel from the supermarkets doesn’t get you as far and was wondering if the main brands where he buys his have changed the formulation somehow.
Reply to
David Billington
Thirty percent is pretty big. It would be hard to change diesel oil that much without causing engine problems. I wonder if the firmware has been reoptimized for low emission at any cost.
When VW was caught gaming the emissions tests, there was widespread talk of VW being forced to do exactly such a thing - it was to evade such a thing the prompted the cheating in the first place.
Joe Gwinn
Reply to
Joe Gwinn
The old car (tdi) cheated on the emissions - google "dieselgate" and emitted more tiny particles than allowed today. The new car is also slightly heavier (you said it was more luxurious - so more options and more sound deadening material) and with a 1.6 liter engine trying to do the same job the 1.9 did it is working harder - regardless of any weight increase.
Reply to
Clare Snyder
30+% is a lot, indeed. "Gaming the test" - "... has been reoptimized for low emission at any cost." (sic. - raising fuel consumption so putting out more CO2 is irrational?) I did wonder that - keep the performance and low fuel consumption in all normal driving.
There is a broader endemic issue here that any scheme which "locks everything down" (sic.) with a tight system of objective rules for an objective outcome will be gamed. Especially given the tunnel-vision of those swallowed-up in the rules-based-system, who can't see any distance that their "paradise they have imposed" is a tiny-distance illusion. That is a problem which at the moment is only increasing with "Standards", "Regulations" (a Law can set a general duty eg. "Safe, so far is as reasonably practicable" - Regulations can create fractal nonsense for which there is always a way out saying "we did every requirement and here is the filing cabinet proving it" when the reality is something grotesquely different)
Reply to
Richard Smith
The car from the late 1990's was first-principles technically excellent. It predated the highly presciptive emissions rules which might have irrationalities.
Still pondering - where does that extra 30+% of the fuel go?!
Reply to
Richard Smith
As I have mentioned before, I owned a VW Jetta TDI that was recalled due to the VW emission cheating scandal.
I noticed that the speedometer in my Jetta TDI was always 10% above what was reported by my portable GPS unit I was using in the vehicle.
Since the Jetta TDI was computerized, the manufacturer can easily change the parameter in the computer to show a 10% higher than normal speedometer reading (the speedometer reading is proportional to diameter of the tire for the same rpm.
The end result is that my tank of diesel would travel a fictitious extra 10% distance, and thus inflate the MPG value.
Reply to
invalid unparseable
On Tue, 31 May 2022 12:15:40 -0400, Mighty Wannabe <👩ðŸ?½â€?⚕ï¸?👨â€?⚕ï¸?👮👨ðŸ?¿â€?🚒👷@ðŸ?».ðŸ??🎖ï¸?> wrote:
Tire rolling diameter matters. Were the tires identical to those the Jetta came with? Correct air pressure?
Joe Gwinn
Reply to
Joe Gwinn
Joe Gwinn wrote on 5/31/2022 1:01 PM:
OEM tires. All four tire specs were exactly as inscribed on the metal plate inside the door jam. I was the first-hand owner. I'll say it was deliberate. The speedometer reading cannot deviate by 10% due to tire pressure.
My portable GPS unit is definitely correct because the speed from that portable GPS unit always corroborates with the speedometer readings in all the vehicles I have driven.
Reply to
invalid unparseable
On Tue, 31 May 2022 14:14:14 -0400, Mighty Wannabe <👩ðŸ?½â€?⚕ï¸?👨â€?⚕ï¸?👮👨ðŸ?¿â€?🚒👷@ðŸ?».ðŸ??🎖ï¸?> wrote:
OK.
The standard calibration approach is to use measured one-mile markers on selected highways. No electronics involved, so clean and direct.
Joe Gwinn
Reply to
Joe Gwinn
Joe Gwinn wrote on 5/31/2022 4:26 PM:
You'll have to use a stopwatch to time it, then calculate the mile per second, then convert to mile per hour. That will be a really tedious task if you don't use a calculator. So you are wrong. Electronics will be involved.
Reply to
invalid unparseable
On Tue, 31 May 2022 08:17:45 +0100, Richard Smith snipped-for-privacy@void.com wrote as underneath :
I think possibly a fair chunk might be because comparative cars seem to be now much bigger than they were and a lot more comfortable, quieter etc, and presumably that is what the public wants? Quietness and comfort (and crash resilience) are weighty and "small" cars now to my eye are giants in comparison to comparative range models from earlier years, you might research the comparative weights and aero efficiency.
Reply to
Charlie+
The economical "63MPG" (Imperial gallon) car weighed 1~1/2tonnes according to the maker's plate - which if so would be quite heavy for a very modest sized car. ...
Reply to
Richard Smith
KISS 60 MPH = 60 seconds / 1 minute No electronics, no calculator. Less than 60 seconds you are going faster than 60 MPH. More than 60 seconds you are going slower than 60 MPH.
Stan
Reply to
Stan Weiss
On Wed, 1 Jun 2022 00:07:52 -0400, Mighty Wannabe <👩ðŸ?½â€?⚕ï¸?👨â€?⚕ï¸?👮👨ðŸ?¿â€?🚒👷@ðŸ?».ðŸ??🎖ï¸?> wrote:
[snip]
Umm, not so fast. Simply check that the car's odometer shows the same number of miles traveled as the highway mile-markers indicate. No stopwatch or calculator needed, mechanical or electronic.
Joe Gwinn
Reply to
Joe Gwinn
On Wed, 1 Jun 2022 00:07:52 -0400, Mighty Wannabe <👩ðŸ?½â€?âš•ï¸?👨â€?âš•ï¸?👮👨ðŸ?¿â€?🚒👷@ðŸ?».ðŸ??🎖ï¸?> wrote:
[snip]
Umm, not so fast. Simply check that the car's odometer shows the same number of miles traveled as the highway mile-markers indicate. No stopwatch or calculator needed, mechanical or electronic.
Joe Gwinn
--------------------------------- The odometer is mechanically coupled to the wheels but an analog speedometer isn't, and they may not agree.
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Reply to
Jim Wilkins
Yes. In a given car, the odometer directly reporters cumulative distance traveled, as integrated from wheel rotation, while the speedometer includes an added error-adding rate-computation step, so the odometer will be more accurate than double integrating speedometer data.
Joe Gwinn
Reply to
Joe Gwinn

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