[Harbir]

Originally Posted by tsk1979

Even in countries where petrol and diesel cost same, diesels are cheaper to run. A diesel engine if inherently more fuel efficient than a petrol.
In large vehicles, petrols can barely manage 11-12kmpl, however, diesels can often give you 14-15kmpl
That is the reason, Europe is primarily a diesel market.

Please see my previous post where I show, with the example of the Swift VXI and VDI, that diesels are not more economical to run if fuel prices are the same.

The calculations I have shown become non-applicable when the cost of fuel is SO high that savings on diesel overwhelm the differences in the purchase price and maintenance cost of the diesel car. And that happens in Europe where taxes make both fuel horrendously expensive, which, as per my point is again a matter of taxation and regulatory policy.

In the US, where fuel taxes are very low and fuel is cheap compared to Europe or India, diesel cars do not save enough money due to fuel efficiency to compensate for their higher purchase price, and are thus NOT cheaper to run.

Diesel cars are cheaper ONLY when taxation policy favors diesel. Its a paradox, but high but equal taxes on both fuels can favor diesel, as can low taxes on diesel but not on petrol. But low taxes on both will cause diesel to be more expensive to run because the higher purchase cost cannot be compensate for by the fuel cost savings.

[blackasta]

I think we can all agree that somewhere down the line, the govt has to come up with a differential pricing and distribution strategy - subsidized diesel for those who it is meant for, unsubsidized for the personal motor vehicles. How they do it shall be a challenge they have to overcome.

[tsk1979]

Originally Posted by Harbir

In the US, where fuel taxes are very low and fuel is cheap compared to Europe or India, diesel cars do not save enough money due to fuel efficiency to compensate for their higher purchase price, and are thus NOT cheaper to run.

On the contrary, its the emission rules in US which increases the price of diesel cars by a large margin. California clean air law is the main driving force.

[lurker]

One good thing about diesels (or another good thing) is that Indirect injection diesel engines can even run on bio fuels if it comes to that. There are old Lister type diesel engines running on biodiesel, sunflower oil/corn oil/coconut oil etc. It seems diesel engines can tolerate a wide variety of natural oils. If it comes to the crunch and petrol becomes unavailable due to some war or calamity we can use this emergency fuels, though longevity of the engines after this experiment cannot be guaranteed.

A lot of auto-drivers (petrol autos) in my area have been adultrating petrol with diesel in their fuel tanks. It's rumored that 50:40 ratio of petrol:diesel is drivable and probably they lease the vehicle from someone else so they could care less. Only caveat it seems is care should be taken not to fill the tank full of diesel and always pour it into some existing petrol. A lot of stuff like this is going on and seeing the toxic emissions that some of these vehicles manage to emit, it seems there is indeed some kind of adultration going on. It's just that the old favorite Kerosene is out-of-vogue now, and so is the 'old flame' naptha-based solvents sourced from private oil companies.

[RS_DEL]

Originally Posted by tsk1979

Even in countries where petrol and diesel cost same, diesels are cheaper to run. A diesel engine if inherently more fuel efficient than a petrol.
In large vehicles, petrols can barely manage 11-12kmpl, however, diesels can often give you 14-15kmpl
That is the reason, Europe is primarily a diesel market.

A question, and this is not for refuting anything you have said but for clarifying my doubts.

@Harbir has raised a question about comparing apples to apples and oranges to oranges when he says compare turbopetrol to turbodiesel if you want a valid evaluation of both. I am open to correction here if my understanding of what he has said is flawed.

What is your stand on this? Is this contention of @Harbir valid in your opinion? If so, how does the fuel efficiency of both stack up?

[Harbir]

Originally Posted by tsk1979

On the contrary, its the emission rules in US which increases the price of diesel cars by a large margin. California clean air law is the main driving force.

That is also a government regulation/policy issue, this time on emissions, similar to european emissions regulations that tax CO2, favoring diesel cars and their lower CO2 emissions.

But let us look at some numbers. In the US, VW offers the jetta with the 140hp 2.0TDI and the 170hp 2.5 petrol. The TDI costs 9.7% more than the petrol. At their rated fuel economy (28 and 36mpg respectively, average of city and highway), after the 9.7% higher price and lower economy are taken into account at current fuel prices, the TDI does not break even till 155,000 kilometers.

I have already said earlier in this thread that the cost of making diesel cars meet US particulate emissions adds cost. So lets look at the UK. there VW does not offer the 170hp 2.5L 5 cylinder, but it does offer the 160hp 1.4TSI 4 cylinder. The 140hp TDI costs £4% more than the 1.4TSI. Assuming that the price difference between the petrol and Diesel models in the US is doubled compared to what it would be in the UK, the Diesel jetta STILL does not break even compared to the petrol till over 70,000 km.

So, even after the additional cost due to the stringent US particulate emissions are taken into account, you would have to wait till for over 70,000km before you you recovered the extra cost, and actually started saving money. Add the opportunity cost on the higher price of the diesel, the more interest paid on the loan, the higher costs of maintenance of the diesel, and the car's breakeven gets pushed out even further.

But if we assume UK prices of fuel, the breakeven drops to under 40,000km. The european buyer finds advantage in diesel because the fuel is heavily taxed. the US buyer does not because US fuel is taxed low. For him, the breakeven gets pushed out because the US is very stringent on emissions compared to the europeans (rightly in my opinion).

So at the end of the day, which is more economical to run is ENTIRELY a matter of any particular country's regulations and taxation involving the cars themselves, fuel and emissions.

[tsk1979]

Originally Posted by RS_DEL

A question, and this is not for refuting anything you have said but for clarifying my doubts.

@Harbir has raised a question about comparing apples to apples and oranges to oranges when he says compare turbopetrol to turbodiesel if you want a valid evaluation of both. I am open to correction here if my understanding of what he has said is flawed.

What is your stand on this? Is this contention of @Harbir valid in your opinion? If so, how does the fuel efficiency of both stack up?

A turbo diesel will be more fuel efficient than Turbo Petrol.
Its plain physics. Compression ratio and fuel energy content are the factors here.
1. http://en.wikipedia.org/wiki/Diesel_...mal_efficiency
2. Energy content of diesel (volume being same) is about 10% higher than petrol

Due to these two factors, a diesel engine is more efficient than petrol engines.
Take a big diesel SUV, and see it get 14kmpl easily on highways. A similarly powered petrol SUV will give you around 8-9kmpl

Infact due to this higher efficiency, diesels are ruling at Le Mans because they can keep running without pit-stop for longer time.

In petrol world, F1 cars have a compression ratio of 17:1 to maximize efficiency around 18000rpm.

Of course, when you get petrol or diesel for 3-4rs/km, you do not care for FE. Case in point, middle east countries.

However, even in the US, trucks run diesel. Nobody runs petrol trucks. Due to limit on particulate matter in US emission norms, diesels get to be very expensive (urea filtration systems and what not)

Current crop of Direct Injection petrols are very efficient, however, their cost becomes very expensive.
A DI Turbo petrol will not be cheaper in purchase and maintenance as compared to diesels.

So when you compare maintenance of Petrol vs diesel, you will find that turbo petrols also cost the same as upfront purchase and then cost the same to maintain. However, for long haul (200,000 miles), the diesel engine will last longer due to its use mostly in the lower rpm range, thus having fewer revolutions under the belt.

Lastly coming to fun point its subjective. Many people like to have loads of torque at low rpm. Some like that high rpm kick which petrols give you. That said, if drag racing is your objective, a turbo petrol will smoke your turbo diesel.
However, if lugging ability and low end driveability is your goal, a turbo diesel will kick the turbo petrol.

[ninjatalli]

^^Excellent points @tsk1979.

Originally Posted by Harbir

Let us discuss some real world examples. Let us compare the petrol and diesel swift.

...

The argument has also been made that even if fuel prices were the same, the diesel would still sell because of better fuel economy. Lets figure it out:

...

VXI = 5.4 + 7.3 = 12.7 lacs
VDI = 6.6 +6.3lacs = 12.9 lacs.

Are diesels really more economical? NOPE. Not unless government policy favors diesel cars.

You make one erroneous assumption - the price difference of 1.2 lakhs in the above example would not be so once the fuel price difference goes down.

Originally Posted by Harbir

Are diesels really more economical? NOPE. Not unless government policy favors diesel cars.

And try doing that illustration with a non-Maruti/non-Swift vehicle, and you might see the disparity go even more larger. After all not everyone drives a kitna deti hai vehicle.

P.s. It might go either way, depending on the vehicle. However on a general basis I'd say the km/l divide will increase.

[Harbir]

Originally Posted by RS_DEL

A question, and this is not for refuting anything you have said but for clarifying my doubts.

@Harbir has raised a question about comparing apples to apples and oranges to oranges when he says compare turbopetrol to turbodiesel if you want a valid evaluation of both. I am open to correction here if my understanding of what he has said is flawed.

What is your stand on this? Is this contention of @Harbir valid in your opinion? If so, how does the fuel efficiency of both stack up?

I am sorry that I have been misunderstood. When I compared them, I was not comparing turbo petrol to turbo diesel on fuel economy but on driver appeal.

I never said turbopetrols are have better fuel economy than turbodiesels.

I was simply saying comparing a 1.2 normally aspirate petrol engine with a 1.3 turbodiesel motor on driver appeal in order to determine whether diesels are more fun than petrols is not a valid comparison.

If the idea is to determine which engine type is more "fun", compare engines of similar cost. In the swift the diesel costs 1.2lacs more. use that 1.2 lacs to turbocharge the petrol swift, and you'll see which is more fun to drive.

THis was in response to those who said they would prefer diesel even if economy was not a question because of the better performance. They're better because they're turbocharged and priced accordingly. In heavy SUVs, as opposed to sports cars, diesels will always have a huge advantage. but I wasn't talking of SUVs. I was talking of cars. Diesels are more appealing for SUVs for sure.

[babu.sundaram]

Yes, it is a baby step towards reducing the skew.
Is it enough? No.
Is it permanent? Not likely (if petrol also goes up).

Diesel engine is bound to be much more complicated / stressed machinery; so it is bound to be expensive than petrol. This is offset by the increased fuel efficiency (+cost). Even if fuel prices are free market and emission norms are normalized, in Indian scenario at least, buying a diesel would make sense if and only if running is high. With this fuel price hike of 5 rs, the break even which was 60K has probably become 65K KMs.

Now, there are 4 classes of people based who they are and what could be their decision:
- High runners who know they are high runners - Would have bought diesel before, would be diesel now - Difference.
- Low runners who think they are (or would be) high runners - No change again.
- Low runners who know they are low runners - Petrol before diesel hike, petrol after as well.
- High runners who think they will run low - Unlikely case, but again no change in their decision as well (petrol).

So, with 5rs hike (which is likely to be revised), would it end the skew on car sales? No way!

[RS_DEL]

Originally Posted by Harbir

I am sorry that I have been misunderstood. When I compared them, I was not comparing turbo petrol to turbo diesel on fuel economy but on driver appeal.

I never said turbopetrols are have better fuel economy than turbodiesels.

SUVs, as opposed to sports cars, diesels will always have a huge advantage. but I wasn't talking of SUVs. I was talking of cars. Diesels are more appealing for SUVs for sure.

I am aware of the limited comparison you made with respect to the performance characteristics.

My question to @TSK was based on the same premise i.e. use similarly constructed engines which consume different fuels and evaluate for fuel efficiency. My reference to your statement was because I found merit in your rationale, that's all. If again I am failing to understand the subject, then it is best I stop trying be a technically aware wannabe.

[Diesel_convert]

Whether it's petrol or diesel the compression ratio determines efficiency, higher the compression ratio of the engine greater the cost as the pressures inside the cylinder are greater. Mixed cycle gdi turbo petrols cost as much as a good diesel. But a petrol won't last as long due to fatigue loading on the crankshaft. As rpm goes up the forces acting go up by rpm squared. But increase in torque results in linear increase in force.


With regards to pricing even though I just bought a diesel , I wish they remove the subsidies. As this is one of the major factors preventing widespread adoption of bio diesels in India.

With bio fuels the money doesn't go out of the Country but to the farmer

[tj123]

I think for the government to manage this private usage of diesel is to create a policy which slowly shift the usage of private diesel vehicles to other alternative fuels like CNG/LPG/Electric/Hybrid. This way government will have a control over registration of private diesel vehicles over a period of time and manufacturer’s will know and plan their product profile based on the policy guideline.

The problem is that lot of these tough decisions have to be taken which impacts a lot of big players and hence it takes lot of political will to take up such a tough stand. I can imagine the pressure under which MMS is working

[Harbir]

Originally Posted by ninjatalli

^^Excellent points @tsk1979.


You make one erroneous assumption - the price difference of 1.2 lakhs in the above example would not be so once the fuel price difference goes down.

Certainly. In the UK the Swift DDIS is 10% more expensive than the 1.2 petrol (In reference to the earlier discussing about US pricing, this also highlights the US model non turbo petrol jetta being 10% more than the turbo diesel is not out of line with europe)

If we assume the same difference for the INdian market, then the compared to the 5.4Lac VXI, the the VDI would be 5.95lacs. That would make the the total costs 12.7 for the petrol and 12.25 for the diesel.

So at that price it would be slight more rather than slightly less economical. Add in the higher maintenance cost of a turbo diesel engine over the span of 150,000km and there would be no case to make about diesels being more economical.

[aravinrd]

My thought is, why can't the Govt think about negating the loss on subsidised diesel (on pvt vehicles only) by collecting a premium (some thing like the education cess ) while the car owner comes for renewing his insurance?