Originally Posted by RoadWarriorFromLP (Post 6999918)

I don't have an issue with diesel, per se, but it is no panacea and I don't see it as being particularly eco-friendly or providing a viable alternative.

Originally Posted by fatbrit (Post 6999932)

The only viable alternative

Originally Posted by RoadWarriorFromLP (Post 6999918)

I don't have an issue with diesel, per se, but it is no panacea and I don't see it as being particularly eco-friendly or providing a viable alternative.

There are a lot of diesel fans out there, I know, but there seems to be a basic misunderstanding of why they get better fuel economy.

To put that into context, let's understand that CO2 emissions per mile are related largely to mpg. It's true that diesels do tend to get more miles per gallon, but here is the primary reason: because diesel fuel has a higher oil content. There is more energy contained in a gallon or liter of diesel than in petrol, but that reduces the quantity of gasoline that could be otherwise produced by a greater amount.

A barrel of oil is comprised of many components, including those that make up gasoline and diesel. The refining process can change the mix a bit, but a barrel still inevitably has some of each.

When you look at from a macro view, the diesel doesn't really create benefit.

If you produced more diesel, you would end up with fewer units of fuel, because of the higher oil content in the diesel fuel. Since you need more oil to produce a quantity of diesel than you would an equal quantity of gasoline, you haven't saved anything.

Diesel motors do have a slight inherent technological advantage because they run with higher compression ratios. However, as gasoline engines evolve in their ability to run at higher compression, that benefit will be negated.

Diesel motors also get a slight benefit from the fact that they are turbocharged. But those benefits can also be gained by turbocharging gas engines. By replacing larger naturally aspirated (non-turbo) motors with smaller turbo'd versions, the same advantages can be gained by gas motors.

Also, the cleaner emissions from ULSD come at the expense of some lost fuel economy. The trend here is for diesels to lose advantages while gas engines gain advantages in comparison, so migrating toward diesel would be a move in the wrong direction.

The US already consumes a lot of diesel, it just does so with its heavy equipment, rather than with passenger cars. There is no benefit to be gained by trying to change this mix.

The inevitable result would be to raise the pump price of diesel fuel, because US refineries would have to be modified at great expense to change their refining mixes if the shift was dramatic enough, and the consumer would have to foot the bill.

The US could end up like Europe, which has had such a dramatic increase in diesel consumption that it has resorted to importing diesel fuel while simultaneously exporting refined gasoline, because its refineries are also not capable of handling the demand. If you want to know why European diesel prices have been rising more quickly than gasoline prices, despite the tax differences, that explains much of it.

Biodiesel is no solution, either. There is no way to produce enough of it to make a significant difference. Even in the best case scenario, the world could not meet more than 5% of its diesel needs with biofuel. The EU 10% standard is a bit ridiculous, as their use of it will only take it away from someone else.

Originally Posted by Steerpike (Post 7000356)

Thanks for the great explanation of the 'world of diesel'. If I may try to summarize what you wrote, Diesel has a higher energy content that gasoline, which explains why you get better mpg from it, but starting with a barrel of oil, you get less diesel from it than you would gasoline, so there's no real net gain in efficiency of resources.

Diesels have been traditionally noisy, less smooth, and produced more particulate matter. If all these issues have been addressed, then I guess there's no big objection to diesel, but there doesn't seem to be any compelling reason to switch over to it either, based on what you've said. With tremendous strides in battery technology, and hybrid powertrains, it seems that is where R&D should go.

Finally, The US has far hotter temperatures than Europe; does that have any impact on the pollution issue? Does diesel 'exhaust' fare well in an Arizona-like environment?

Originally Posted by Steerpike (Post 7001470)

If 90% of workers are making $70/hr for factory line work, etc, I may be less sympathetic...

Originally Posted by Steerpike (Post 7000356)

Thanks for the great explanation of the 'world of diesel'. If I may try to summarize what you wrote, Diesel has a higher energy content that gasoline, which explains why you get better mpg from it, but starting with a barrel of oil, you get less diesel from it than you would gasoline, so there's no real net gain in efficiency of resources.

Diesels have been traditionally noisy, less smooth, and produced more particulate matter. If all these issues have been addressed, then I guess there's no big objection to diesel, but there doesn't seem to be any compelling reason to switch over to it either, based on what you've said. With tremendous strides in battery technology, and hybrid powertrains, it seems that is where R&D should go.

Finally, The US has far hotter temperatures than Europe; does that have any impact on the pollution issue? Does diesel 'exhaust' fare well in an Arizona-like environment?

Originally Posted by Cape Blue (Post 7001739)

Diesel has approx 15% more fuel energy per unit volume than petrol, due partly to this and mostly the higher efficiencies of the diesel combustion cycle it produces around 50% higher efficiency in mpg terms so there is a significant net gain at the vehicle.

Originally Posted by Cape Blue (Post 7001739)

Diesel has approx 15% more fuel energy per unit volume than petrol, due partly to this and mostly the higher efficiencies of the diesel combustion cycle it produces around 50% higher efficiency in mpg terms so there is a significant net gain at the vehicle.

I have wondered why we have yet to see more diesel hybrid vehicles as that would seem to give the town driving advantage of electric along with the freeway advantage of diesel.

Diesel emissions are an issue in high sunlight areas as they are more prone to creating smog, hence the Los Angeles/CA driver of low emission standards.

Originally Posted by RoadWarriorFromLP (Post 7001798)

I'd say that 50% is a gross overstatement, when apples-to-apples comparisons based upon like performance are made. The difference is closer to a maxmum 25-30%, on the lower end when ULSD is being used.

Here's a real world example that compares a gas turbo (which I've done in order to compare one turbo to another) with a turbodiesel -- the UK spec Audi A4. According to WhatCar? -

-the 2.0 liter gas turbo quattro has a 0-60 time of 6.6 seconds, with a top speed of 153 mph. It has average fuel economy of 38.2 mpg (UK gallons.)

-the 3.0 liter turbodiesel quattro has a 0-60 time of 6.1 seconds, with a top speed of 155 mph. It has average fuel economy of 42.8 mpg (UK gallons.)

-the 2.7 liter turbodiesel FWD has a 0-60 time of 7.7 seconds, with a top speed of 140 mph. It has average fuel economy of 44.1 mpg (UK gallons.)

To get similar performance from a diesel, you need to get a bigger motor, plus turbochargers are essential. In the case of the 2.7 liter, you get a 15% mpg advantage, but the trade off comes with lower performance.

The 3.0 liter turbodiesel outperforms the 2.0 liter petrol engine, but it requires 50% more displacement to get there, and has a fuel economy advantage of only 12%.

The only way to get 50% results is to compare high performance gas engines with smaller, slower variants of the diesels. If you compare based upon like acceleration and top speed, you won't get anything close to that.

Originally Posted by Steerpike (Post 7001809)

My biggest concern about diesel is how the engines age. Diesel engines have to be built 'stronger' due to their higher compression, and thus, they tend to last a lot longer (they also have fewer moving parts, as I understand it, which further helps extend their life). But - as they age, they also get 'sloppy' and produce a lot more emissions. Couple that with the fact that, in CA, cars don't rust so if the engine keeps going, the whole car tends to last forever. I can't tell you how many ancient Mercedes Benz cars I get stuck behind, watching them belch out clouds of black smoke. Add to this the rule that, in CA at least, you can't be required to spend more than '$x' to fix an emission problem on an old car, and you are essentially building something that is almost guaranteed to produce pollution 10, 20 years down the road.

Maybe the trick is to implement stricter emissions rules on older cars - eliminate the cap on repair costs. I believe in Japan they all but retire cars older than a few years to 'force' higher safety and emissions (and keep the auto-industry healthy!).

Originally Posted by Cape Blue (Post 7001852)

I took the info from wiki

Originally Posted by Steerpike (Post 7000356)

Finally, The US has far hotter temperatures than Europe; does that have any impact on the pollution issue? Does diesel 'exhaust' fare well in an Arizona-like environment?