But for simplicity, just assume the euro cycle instead of analyzing BSFC plot, you can compare to same (or lower/slower in this case) power diesel and the economy is still well within range of my estimate. 4.2 l/km (65kw diesel) + 20% or 5.5 l/km (77kw gas) -20% density diff ~= 10% more fuel mass use for engine with 15% more power.

You realize that list is not using any modern gas engine. I noted FSI for a reason.

The 2008 Orbital engine (Revtech report) seems pretty modern to me. YMMV.

A 1.2 FSI doesn’t seem very comparable to a 1.9TDI PD.

# Performance: 0-62mph in 16.5 secs, max speed 97mph, 50.1mpg
# Tech: 1198cc triple, FWD, 64bhp, 83lb ft, 1143kg, 151g/km CO2

Perhaps you can post some better numbers and some links to support your case?

If not, there’s not much point in continuing.

Cheers,
Scott.

Hint – diesels are more efficient (even when measured by BSFC) and will continue to be. (BTW, note that the LHV (usable energy per mass) of diesel is only about 1% higher than gasoline.)

You realize that list is not using any modern gas engine. I noted FSI for a reason.

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Why should maximum power be the metric for comparing automobile engines?

Because it measures how fast a car can accelerate, which is the point of an engine.

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What’s most important for real-world driving is torque in the most commonly used RPM ranges.

That’s why they invented transmissions. BTW, in the future, try to use the relative curves instead of absolute value to avoid embarrassment.

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In 2004 VW offered 3 engines in the US Jetta wagon with a 5 speed manual transmission.

They specifically offer the only expensive gas engine as a performance model, and the diesel with high “mileage” green number for dumb people who don’t understand density.

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Finally, remember the Audi LeMans TDI engines. Whadayouknow – they get better mileage and still won!

You realize they were only really competing against another diesel, right? (and just lost)

If you want to discuss le man technicalities we can do that, but you need to realize this is a nuanced issue surrounding cell capacity (pit strategies) and minimum weight.

Again, those of you who tout the MPG just don’t understand this at all.

The MPG of gas and diesel can’t be compared because the fuels are different! Diesel contains more oil, so a barrel refined to produce a higher ratio of diesel produces fewer gallons of fuel overall. Making more diesel for you takes away a disproportionately higher amount of gas from the rest of us.

MPG is only relevant when comparing like fuel types (gas to gas or diesel to diesel). MPG cannot be used to compare different vehicle types.

Study some chemistry, and this will become more obvious. Just because you purchase fuel by volume does not mean that it makes for a relevant scientific comparison when discussing “efficiency.”

Thanks. The 2.8 litre mileage number was from the EPA, I just assumed it was a VR6. I’ll fix it.

Cheers,
Scott.

The 2004 Passat wasn’t available with any kind of VR6. The 2.8 in the Passad was a conventional V6.

You can use these arguments until stratified direct injection (or homogeneous w/ turbo) becomes common.

When will that be? And, just to be clear, are you arguing that (comparable generation) gasoline engines can overcome the inherent advantages of diesels? Hint – diesels are more efficient (even when measured by BSFC) and will continue to be. (BTW, note that the LHV (usable energy per mass) of diesel is only about 1% higher than gasoline.)

For example, a simple straight comparison should be for the 1.2 fsi vs the 1.6L tsi both around 77kw, but only the 65kw version of the diesel is available in the polo.

If trees were made of stainless steel then forest fires wouldn’t be a problem. :-/ It’s a rather academic argument if the engine isn’t available, isn’t it? Why should maximum power be the metric for comparing automobile engines?

Comparing mileage means comparing distance traveled per volume of fuel. In 2004 VW offered 3 engines in the US Jetta wagon with a 5 speed manual transmission. Their city/highway mileage ratings were 21/28 1.8T (premium gas), 21/28 2.0 (regular gas), 31/42 1.9TDI PD. (The 2.8 litre V6 (which wasn’t offered in the Jetta) gave 17/26 (premium gas) in the 2004 Passat Wagon.)

Comparing maximum power developed between gas and diesel engines is comparing apples and oranges. Diesels have a redline around 4500-4700 rpm so gas engines will always have more maximum power for the same displacement (and similar generation). What’s most important for real-world driving is torque in the most commonly used RPM ranges. Picking 2500 rpm for the engines, the 1.8T has about 168 lb-ft, the 2.0 has about 122 lb-ft, and the 1.9TDI PD has about 177 lb-ft. (The VR6, offered in the Golf and GTI, has about 195 lb-ft.)

So, of the engines available for the 2004 Jetta wagon, the 1.9TDI PD gives more torque at usable rpms, and gives substantially better mileage than the comparable 1.8T gas engine.

You can spin it all you want, but in the real world TDIs get substantially better mileage than comparable gas engines.

Finally, remember the Audi LeMans TDI engines. Whadayouknow – they get better mileage and still won!

· The winning car’s average speed over the entire distance was 215.409 kph (133 mph).

· Thanks to the economical Audi V12 TDI engine, the Audi drivers only had to pit for refueling once every 14 laps. The winning car used only approximately 41 liters of Shell V-Power Diesel per 100 kilometers (5.7 mpg) – for a race engine producing more than 650 hp and more than 1100 Newton meter (810 ft.-lbs.) of torque – an extremely low figure.

· In the closing laps of the race the Audi drivers even completed as many as 16 laps on a single tank of fuel (approximately 13.2 mpg). Tom Kristensen was the first driver to achieve this.

HTH, but I figure it won’t change any minds.

Cheers,
Scott.

What? That’s in my first post right up at the top. Look, to help out your argument in the future, you should also notice that gas engines use throttles which decreases pumping efficiency and only tend to achieve max efficiency at around max torque engine speed. You can use these arguments until stratified direct injection (or homogeneous w/ turbo) becomes common. The graphs I used are for FSI with quite generous allowances for diesel.

For example, a simple straight comparison should be for the 1.2 fsi vs the 1.6L tsi both around 77kw, but only the 65kw version of the diesel is available in the polo.

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there are many ways to fraction crude, but are you saying there should be some perfect fractionation to do this and we should require the refining industry to follow this perfect model

Refineries are designed for an approximate ratio. This is why diesel is more expensive in the winter due to market competition for light oils (heating).

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So in making more gasoline, you are robbing from the Diesel stock.

As already belabored many times, hydrocarbon mass is conserved. Any necessary conversion is reasonably efficient. Thus with higher density of diesel, you’re just packing more HC’s into it. HC’s are what you buy in crude, using more of them leaves less of what you just bought left. Thus, any technical comparison needs to be by fuel weight and not volume.

The Lupo 3L was a much, much smaller car than the Fiesta, used exotic materials and thin glass, had a extremely annoying automated manual… but it got a 80 mpg Euro rating.

I made the casual remark on density towards the very top of the comments. Thus far, I’ve seen nothing on mass density vs. energy density vs. specific energy yet. I’m actually kind of curious how much the discrepancy between the former and latter ratios for gas/diesel is a matter of base chemistry of hydrocarbon length or practical combustion realities. Where are these nuances you speak of?

Yeah, it’s like 5-10% more efficient based on what I’ve seen of BSFC numbers assuming similar level of tech/cost in engines. Big deal.

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I know very well that Diesel has more energy content than gasoline and regard that, given Diesel’s near price parity,

Why don’t you read the link and comments you posted yourself from the Oil Drum to find out how the petroleum derivatives are created. The reason why it may be off from hydrocarbon per $ price parity has more to do with refinery design/mix and market demand for light oils in addition to diesel.

Density matters because one of the fundamental arguments for diesel is using less oil. Well you don’t use less oil just because you can fit more of it into the same volume for storage.

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gasoline is the more righteous fuel, so none of that matters, and those that appreciate the Diesel are fools and mountebanks

They can’t seem to understand very basic arguments, so make your own judgment as to how smart they are.

But of course, for Pch101, gasoline is the more righteous fuel, so none of that matters, and those that appreciate the Diesel are fools and mountebanks

those Toyota Corollas from the 80’s last 500K miles without problems, too. The engines today are just great, no matter if they’re gasoline or diesel.

Being that’s a critical point that diesel fans must ignore to feel content with their arguments, there is no reason to set it aside.

As noted, diesel does have the advantage of higher compression. But the MPG argument needs to be torpedoed for the fallacious indulgence that it is. Every time I read it, I wince, as it is obvious that the people making it don’t understand it.

Diesel fuel packs more energy into a quantity of fuel, consuming more oil in the process. If you don’t understand the implications of this, then you will be missing most of the equation.

Here’s one of my understandings:
Set aside the matter of energy content of gas and diesel, the Diesel engine is inherently more efficient than the Otto engine as a matter of thermodynamic realities.

You’ve got it. Comparing the MPG of a gasoline vehicle with the MPG of a diesel vehicle makes no sense. It’s reasonable to compare gas to gas and diesel to diesel, but they are different fuels with different characteristics and comparing them directly with each other is misleading, as this discussion makes clear.

It’s how much refined oil was used per mile is what really matters.

Mostly true, although because oil contains both gasoline and diesel, we may as well use both (which we already do.) It would be truly wasteful if we were to throw away gas or diesel due to overproduction of one of them at the expense of the other, but we aren’t doing that and probably never will. (We used to back during the 19th century, but today, we extract value from everything in a barrel of oil, from asphalt to jet fuel to gasoline.)

From an efficiency standpoint, the gas vs. diesel discussion is obviously misunderstood by the average diesel fan. Diesel really is slightly more efficient due to the higher compression of diesel engines, and it often is in the real world because of the widespread use of turbocharging. But the MPG argument is obviously bogus, and the turbocharging benefits can be gained in a gas engine just by installing one.

Exactly.

http://www.laweekly.com/2006-07-13/news/the-crisco-kid/

it probably references this, whose study link is broken

http://www.dft.gov.uk/rmd/project.asp?intProjectID=11610

I seriously doubt whatever podunk backyard operation is testing emission properly with their combination of viscosity solution and whatever car they’re using.

“Eggsalad’s processing also probably results in a very polluting car, even greater than the usual carcinogenic nature of diesel exhaust.”

Processing? What processing? I run it through a 10-micron filter. Explain to me how vegetable oil is more carcinogenic than Diesel fuel, please.

I get what you’re saying. It takes X gallons of oil to make gasoline and it takes Y gallons of oil to make diesel, and Y > X.

So because of that, the diesel car goes further on a gallon of diesel than a gas car goes on a gallon of gas, since there’s more energy content in a gallon of diesel than in gasoline.

The ultimate question isn’t how many mpg’s you get with diesel vs gasoline, since they’re two different measurements. It’s how much refined oil was used per mile is what really matters.

Now what I don’t understand is, even with the difference in energy content, which is more efficient? Diesel engines or gasoline engines?

It would greatly benefit you to realize that hydrocarbon mass is more or less conserved in the process.