You want to compare a car that needs 11.2 seconds to get to 60 mph (the 1.9 TDi) with one that needs 8.6 seconds to do the same thing? (For this, I've used the UK-spec Audi A4's per the Whatcar? website.)
My point has been that higher performance engines tend to use more fuel, whether gas or diesel. You do realize that this fuel economy margin would shrink if you compared it to a gas engine with similarly weak performance?
Guys.... Just go to the Honda UK website. There you can see the relative performance of the various sized gassers to the 2.2 diesel. In the end, it's which engine comes in the car that best suits your needs. You can only buy what the mfg. offers you. The civic diesel is relatively quick.
You're right, of course, but one shouldn't compare Honda Fits with Bentleys and believe that we are on an even playing field here, if you know what I mean.
Here's a better comparison than the one previously offered using the 1.8T gas engine cited before. Again, this is of two Audi A4's sold in the UK: the aforementioned 1.8T gas engine, and the 2.7T diesel. They have similar specs for horsepower (161 hp for gas vs. 178 hp for diesel), 0-60 mph acceleration (8.6 vs. 8.4 seconds) and top speed (142 mph vs. 139 mph).
As expected, the diesel gets better fuel economy, in this case 22% better overall, and 19% better on a city cycle. That's fine, but that's not 37%. That's the kind of exaggeration that I'm talking about.
This example also points out the power differential between the two engine types. The turbo diesel engine has to be 50% larger to achieve similar output to the turbo gas engine. You can't compare similar displacements and get a fair comparison.
I don't think you two read the article properly. It stated the comparison between two engines with the same torque curves and different horsepowers. Torque is used to get the vehicle moving with transmissions using smaller gear ranges. (Pulling loads). If you want speed (top speed) you need larger gears. So the answer to the question between diesel engines and gas engines can't be truly answered here. Diesels produce higher torque at lower rpms for engines of the same displacement. The torque converter's stall speed is the most important part of getting off the line with automatics and clutch engagement for manuals. If you let the clutch out too quickly, (Below the required torque value for the given gear), You will stall the engine. This is really important at lower speeds. After the minimum torque requirement has been satisfied horsepower becomes all important. Its all in the gearing. With diesels you use smaller gear ranges but more speeds to overcome the lack of horsepower at high rpms. With gas engines higher gear ranges can be used due to more horsepower, but will need a lower first gear to multiply the lower torque so not to stall the engine under load. Slower off the line from idle, due to the delay of gear engagement. If you have an automatic with a high stall speed converter or rev up the engine and let your clutch out slower then you might beat the diesel off the line. But over time the higher torque of the diesel will have less ware on the clutches or torque converter. (It will live under the abuse longer). The common turbo diesels are quicker off the line then common gas power vehicles of the same mass. (As long as the gas engine is not supercharged). But once you get over 10 to 15 MPH the gasser should have the advantage due to taller gears and more horsepower. If either is geared to take advantage of it's strong point both will surprize you. But if you really want speed buy a Corvette. Buy the diesel if you want better fuel economy or to pull loads (Tow the Corvette).
For sure it is about what I said about different solutions to problems. Again if one is hung up on acceleration and power it is a no brainer on where to go; Corvette, exotic etc. My take on diesel, especially on USA roads is really how well suited it is or can be. Since the passenger vehicle fleet populations of diesels is 2.3-2.9% I think it is fair to say the majority of gasser folks have no real experience with diesel cars. That is fine with me, but this is a diesel thread, so I am talking diesel.
But once you get over 10 to 15 MPH the gasser should have the advantage due to taller gears and more horsepower.
I was making this point by comparing 0-60 times. That's a common benchmark when evaluating vehicle performance, and it's fair to do this here.
Buy the diesel if you want better fuel economy or to pull loads.
I also acknowledged this -- remember my comment about semi's and locomotives. But passenger cars aren't meant to pull heavy loads, which makes that an unimportant consideration when shopping for sedans. And the fuel economy difference when comparing like vehicles is not going to be 37% -- the diesel will have better fuel economy, but it won't be quite that much. Let's have accurate data here, not exaggeration or misplaced comparisons.
"And the fuel economy difference when comparing like vehicles is not going to be 37% -- the diesel will have better fuel economy, but it won't be quite that much. Let's have accurate data here, not exaggeration or misplaced comparisons." Well here I don't agree. What are the numbers for the Jeep liberty CRD 2.8L and the liberty 3.7L gas engine. Vehicles same size and mass. Then use a VW jetta TDI and gas engine with about the same displacement then compare. My CRD averages 26.5 MPGs most 3.7 gassers average about 20. I had both and drove them the same. The CRD beat the EPA estimate and the Gasser never got it. But you two need to stop fighting and agree to disagree.
Then use a VW jetta TDI and gas engine with about the same displacement then compare.
You're making the same mistakes that ruking is:
-You compare turbodiesels to non-turbo gas engines, while forgetting that some of the fuel economy benefit is derived from the turbo. The whole idea behind turbos is to increase peak power capacity without needing the mass that would be required to generate it with a normally aspirated engine, which improves fuel economy. Compare turbos to turbos to get apples-to-apples.
-You forget that higher output engines tend to have lower fuel economy, no matter what. A powerful gas engine uses more fuel than does a less powerful gas engine. A more powerful diesel will use more fuel than will a less powerful diesel.
This stuff is all pretty basic, folks. If you want to compare weak engines and strong engines, then don't be surprised that the weaker motors use less fuel. This is just how internal combustion works -- you can't produce power without consuming energy.
"And as noted by the other poster, the torque stops being relevant at a very low speed. It doesn't matter when getting to highway speeds, or even at speeds driven on your typical residential street."
Don't twist my words. It's all in the gearing!! And diesels accelerate better in residential driving due to quicker shifting from stop sign to stop sign. You don't have to drive as aggressively as a gasser. Its more pleasurable. You need to drive a diesel to know the difference in driving characteristics between the two. A gasser feels like your winding up a loose rubber band. The diesel goes right into gear and pulls without letting up till you let it. I like the diesel better for everyday driving. I prefer a corvette if I want to feel the engine work and work myself driving it.
I would agree. I actually wish I had a tad more power and VW oem would have put a 6 speed manual, as another poster had mentioned about the Skoda. That trans I know is far beefier than mine, even as I know the 5 speed that came with mine can with reasonable care go 400 to 500k.
You need to understand why a turbo is used on a diesel. It is to increase the air charge into the cylinder for better combustion the fuel (Better Fuel Economy). It is really not so much to increase the "peak power capacity" but to have more air charge to the cylinder at higher rpms without increasing the intake port size or adding more valves per cylinder. It is also for emissions and better performance at higher altitudes. The max boost pressures are around 23 PSI and the direct injection of the fuel is where performance is increased most. Take the turbos off and you would choke the poor soul behind you. What you are stating is for a gas engines with a turbo.
Did you forget or not know that a gallon of diesel contains 10% more energy then a gallon of gas and the diesel cycle is more efficient and a more complete combustion of the fuel the a gas engine. These are facts. Look them up. You can't get something from nothing. Diesels are around 37% more fuel efficient per gallon then a gas engine! It's Physics!
Diesels are around 37% more fuel efficient per gallon then a gas engine!
Come now, I just spent the last several posts showing how obviously flawed this statement was. If you guys want to compare low output engines to high output ones, then you're well off track.
Otto cycle (Gas Engines) efficiencies range form 20 to 25%. Diesel cycle efficiencies are about 40%. So 40-25=15, 15/25=60% improvement over a gasser. Diesel also has 10% more energy per gallon then gas so 37% better fuel economy is not unrealistic. But it must be noted that a gas engine running at peak power is just as efficient as a diesel. But only at peak power. So in the real everyday world diesels get about 37% better mpgs then gassers!!!!!!!!!!!
really, pch. 37% is a lower bound, depending how we're counting! better efficiency of diesel engine. more energy content per gallon of fuel. these things are not debatable, they are established and measurable facts. so it's pretty funny when you try to debate against established facts. it's also semi-funny to see people arguing whether it's torque or horsepower which is more important to acceleration, or whether it's "all in the gearing". observing engine torque curves and comparing with dyno output graphs can be interesting - look what happens at the shift points - look how the gearing affects the dyno output at various rpms.
1. Does not take into account that all new diesel powered vehicles will have PM traps. 2. Article does not take into account that S15 diesel fuel is now the norm. 3. Article does not mention the use of biodiesel and that fewer pollutants are produced when this fuel is used. 4. Article ignores the fact that there many other sources that show that it is far more energy intensive to make ethanol than biodiesel. 5. Date of article is April 2005. Lots of things have changed since then.
Yes, I think there are indications that the market is picking up. While this hasn't happened yet, almost all the oems are getting into the USA market fray.
Of course, the biggie three have been in it for a long time GM, Ford, Dodge, but in the bigger light truck market.
When you compare/contrast this with the "dip the toe in the water" progress with the hybrid, it is even more remarkable.
If one uses the Liberty diesel as an example, I am sure the oem wished it had 2x the products of 11,000 that it produced in that first year, to sell.
VW in 2003 had 4% of their products diesel. I also think they probably could have sold 2x or eight percent of their product line. They surely NOW sell every diesel, even before it hits the lot.
I also think a lot of the changes has to do with the increases in the R and D dollars and commitment to invest to the diesel segment. It would not be too financially good to put HUGE percentages of R and D money to a declining market segment, either to lack of interest or regulatory efforts at diesel extinction. People are increasingly recognizing the utility of being ABLE to use an alternative fuel. One imediate pay off's is the much better mpg on like models. In the case of the 2003 VW Jetta, 37%.
There has been a news item that Iran could possibly run out of oil in 2015. It is good that folks are realizing they can vote with their dollars, even as Iran and others are cutting back their production to firm up sagging prices. Another interesting news item was the -54 AVERAGE mileage from 2004 to 2005. While this is FAR less than one half of one percent, .0039384, it is evidently having a Tsunami effect. Imagine what a 37% FUEL DECREASE would do!!
OK, points all taken. But the gist of the article and the questions I had raised have not changed because of these facts from the article:
"Making a gallon of diesel fuel requires 25% more oil and emits 17% more heat-trapping greenhouse gases than gasoline reformulated with MTBE. Similarly, diesel requires 17% more oil and emits 18% more heat-trapping gases than gasoline reformulated with ethanol. This means that diesel fuel's advantages from its higher per-gallon energy content and better performance on greenhouse gases are partially offset by the impact of diesel's fuel-production process."
and:
The improved efficiency of diesel engines can also help reduce oil consumption. It should be noted, however, that it takes about 25% more oil to make a gallon of diesel fuel than a gallon of gasoline, so we should really look at how a vehicle does on fuel efficiency in terms of "oil equivalents." Thus, we need to adjust the mileage claims for diesel vehicles downward by about 20% when comparing them to gasoline-powered vehicles.
So with that in mind, Ruking1's 37% is not an effective number. The 37% might apply ONLY to the VW TDI vs gasser example he is presenting, and that could very well just have to do with the higher gearing that VW sets.
..."So with that in mind, Ruking1's 37% is not an effective number. The 37% might apply ONLY to the VW TDI vs gasser example he is presenting, and that could very well just have to do with the higher gearing that VW sets."...
Well no, you could look up the uk diesel Civic and compare it with the gasser civic!!?? I'll let you report the numbers. You might think that I am making this stuff up, but I am just doing the math. With the way they shoot messengers around here, I don't think you'd take up the challenge, as you probably already suspect the answer.
thanks for doing the work, BR. I was just about to ... now I'm saved.
I also want to add, however, the Audi diesel racecar that won LeMans recently. Obviously as good or better than all the gassers, given it won. AND more efficient, allowing it to refuel less often.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
I would agree, if you watch some of these races, they make rocket science and political chess of fuel consumption management. I guess at some level, that does have entertainment value. I even heard that a famous racer (Jeff Gordon) vilify a woman (fwllow racer) , because he had a fatter butt than her. But diesel could moot this whole subplot!!
I was inspired by Larsb's post on that DIESEL super sports car that gets 48 mpg on the race track and 70 mpg on freeway at 62? mph!!! Got to love that twin turbo diesel BEAST !!!
But as gearing being germane to the discussion, I have posted prior that I wish we had the increased power and gearing that say the European available Skoda (do a search for alltorque's posting on the Skoda). Specifically 130 hp/229 # ft of torque vs 90 hp/155# ft of torque and the 6th speed vs the 5 speed. My SWAG is if I didn't put my right foot into it, the MPG would INCREASE at worse 1 mpg to 4 mpg and that is with SIGNIFICANTLY more hp and TORQUE !! The two edged side in effect it would double as a PERFORMANCE machine. Again the right foot is the lead switch to turn on and or off. Whereas now it is really a good road to economy car. So one consequence is an even better mpg car is banned from the USA!! I really would not mind the mpg range being extendded 1-4 mpg. Aint it terrrible the USA regulates in the fuel guzzlers into the market? Give me that 54 mpg pocket rocket!!!
...""..."So with that in mind, Ruking1's 37% is not an effective number. The 37% might apply ONLY to the VW TDI vs gasser example he is presenting, and that could very well just have to do with the higher gearing that VW sets."...
Well no, you could look up the uk diesel Civic and compare it with the gasser civic!!?? I'll let you report the numbers. You might think that I am making this stuff up, but I am just doing the math. With the way they shoot messengers around here, I don't think you'd take up the challenge, as you probably already suspect the answer. "...
..."And good job you want to, as only a buffoon would touch the 1.6 and 1.8-litre petrol alternatives here when faced with such an excellent choice. It's Honda's 140bhp 2.2-litre unit, as used to such wonderful effect in the larger Accord. The paperwork records a top speed of a notch under 130mph and a 62mph sprint of just over eight seconds, but bear in mind that this engine develops nearly twice the torque at half the revs (ie, 251lb ft at 2,000rpm) of the 140bhp 1.8-litre petrol alternative and you begin to get an idea of its superiority."...
..."and intervals at 12,500 miles, this is a reasonable proposition, while the overall 55.4mpg return is very impressive for the class, suggesting a mid-40s fuel consumption in the average mix of driving is feasible...
In reading the article from the UCS it stated that diesel fuel is 25% more costly to produce than gasoline!! Curious I thought that diesel, being the more basic product, was less costly. Not being a petroleum engineer I did a bunch of searches and didn't find much help in understanding the processes of creating oil products. All the references seem to show the same ( or very similar ) results; to wit..
If I read the other searches correctly gasoline being the most volatile component of a barrel of oil is separated first and in the greatest volume ( I'm open to being corrected here ) at the least cost!!
19.6 gal of Gasoline per bbl 10.0 gal of Diesel/Fuel Oil per bbl
Now another question arises. Our dependency on dino fuel?
Let's take two hypothetical vehicles .. Jetta TDI getting on average 40 mpg .. Corolla getting on average 30 mpg The Jetta TDI is 33% more efficient than the gasser Corolla. For a normal drive of 15000 mi/yr the respective fuel consumptions would be.. .. Jetta 375 gal .. Corolla 500 gal
But one barrel of oil produces 19.7 gal of gasoline and 10 gal of diesel fuel. So to supply the Corolla's 500 gal usage it takes 25.5 bbl of oil. These 25.5 bbl also produce 255 gal of diesel. But wait the Jetta needs 375 gal to go 15000 miles. That means that an additional 12 bbl of oil are needed to be processed in order to produce the shortfall that the Jetta needs.
So one Corolla using 500 gal/yr needs 25.5 bbl of oil but the Jetta using 375 gal/yr needs 37.5 bbl of oil?
So diesel is more expensive to produce (?) because more of the base product is needed for the same distance driven because the yield per bbl is lower. That 25% extra base product seems to cancel the 35-40% gain in efficiency of the diesel engine.
But then the pricing is skewed. Diesel is 'only' $.20-$.60 higher in cost than Reg Unleaded. That's not 25%. Ergo The oil companies are subsidzing the diesel users? :surprise: Sure The oil companies are overcharging the more in demand gasoline users?
All the references I have ever seen indicate diesel is cheaper to produce. Part of the reason is diesel is a natural consequence of the refining process. YOU can NOT get to unleaded regular without passing diesel!! The following is not sound bite able, but I have made reference to this flow/concept in a few other posts.
Now when you ADD to that, that unleaded regular is processed from the LSC or light sweet crude which is the price MOST often quoted when they ask daily : what is the price of a barrel of oil? Keep in mind that even refining light sweet crude has as a natural consequence the app DOE 23.81% of #2 diesel fuel. Light sweet crude is MUCH less plentiful than other than light sweet crude and is MORE costly. OTLSC (OTHER THAN) is actually the majority of the barrels of oil pumped from the earth. The upshot is it sells on the open market 30-40% CHEAPER than LSC !!!!!!!!! So as you can probably deduce, because #2 diesel is fungible, the cost is so called "artificially" higher since 23.81% of LSC is diesel processed from the higher priced LSC. So again because #2 diesel is fungible, the oil companies most assuredly sell diesel process from OTLSC for a higher price rather than a lower price because of the fungibility issue. Indeed those types of commodies are openly traded in commodities exchanges such as CBOT etc etc. Of course all have heard of OPEC and its price setting for a barrel of oil. In addition both products gas and diesel are pipelined co mingled and separated out at the end destination terminal, which again incurs host of process and separation fees/cost.
Oh yes, do a google on Chevron. There are of course many others, BP, Shell, to name a couple more. Unleaded regular and diesel have their own divisions.
At your suggestion.. from Chevron's website. ( Bold added for emphasis )
Refining Processes The Modern Refinery Blending About Hydrocarbons Other Compounds Diesel Fuel Chemistry Chemisty of Diesel Fuel Instability Biodiesel
Diesel fuel is made from petroleum. All petroleum crude oils are composed primarily of hydrocarbons of the paraffinic, naphthenic, and aromatic classes. Each class contains a very broad range of molecular weights.
As it comes out of the ground, crude oil can be as thin and light-colored as apple cider or as thick and black as melted tar. Thin crude oils have relatively low densities and thus high API gravities (see below). Therefore, they are called high-gravity crude oils; conversely, thick crude oils with relatively high densities are low-gravity crude oils.
DENSITY AND GRAVITY Density () is the mass of a unit volume of material at a selected temperature. For example, the density of water is 0.9990 grams per cubic centimeter (g/cm3) at 60°F (15.67°C). Relative density (RD) – also called specific gravity – is the ratio of the density of the material at a selected temperature to the density of a reference material at a selected temperature. For the relative density of petroleum crudes and products in the U.S., the reference material is water and both temperatures are 60°F. RD (60 / 60°F) = sample (60°F) ––––––––––––– water (60°F)
The United States petroleum industry often uses API gravity instead of relative density. The following equation relates API gravity, in degrees API (°API), to relative density.
While API gravity measurements may be made on liquids at temperatures other than 60°F, the results are always converted to the values at 60°F, the standard temperature. API gravity is an arbitrary scale developed by the American Petroleum Institute in the early years of the petroleum industry. Density had been used as a primary indicator of quality for liquid products. However the higher value products have lower densities. The API gravity scale was constructed so that API gravity increases inversely to density; therefore, higher value products have higher API gravities. And while the densities of most petroleum products are less than one, the API gravity scale also was constructed so that most values are between 10 and 70.
Refining is the process of converting crude oil into high value products. The most important are transportation fuels – gasoline, jet fuel, and diesel fuel. Other important products include liquefied petroleum gas (LPG), heating fuel, lubricating oil, wax, and asphalt. High-gravity crude oils contain more of the lighter products such as gasoline and generally have lower sulfur and nitrogen contents, which makes them easier to refine. However, modern refining processes are capable of turning low-gravity crude oils into high value products. Refining low-gravity crude oils requires more complex and expensive processing equipment, more processing steps, and more energy and, therefore, costs more. The price difference between high-gravity and low-gravity crude oils reflects the refining cost difference.
So the low grade crude which according to you makes up most of the feedstock for diesel is priced significantly lower than LSC, which by Chevron's implication ( above ) is a result of the higher costs of processing meaning that the net result is approximately the same.
So this still creates the situation that more feedstock oil is needed to derive the 375 gal of diesel needed to power the Jetta. Thus the UCS's estimate of a 20% reducing factor for diesel still seems reasonable. However throw in some locally made biofuel ( 120 gal/yr ) and no additional dino fuel is needed.
Well done. Both gasolene and Diesel come from the same barrel. Not using both would be wasteful. The costs and amounts extracted really depend on what type of crude you start with. The problem is with the lighter crudes. They are favored due the ease of refining and higher amounts of lighter hydrocarbons. Gasolene is lighter and Diesel is heaver. Read this link: http://www.eia.doe.gov/pub/oil_gas/petroleum/analysis_publications/oil_market_ba- sics/refining_text.htm The costs are relative to many factors. With less light crudes available gasolene will become more expensive due to lower supply. Diesel can be had from much heaver crude while the amount of gasolene will decrease.
It's a better comparison than most. However, you are still comparing a turbocharged diesel to a non-turbo gas engine car.
The diesel fans in the forum seem to forget that turbocharging provides fuel economy improvements to both gas and diesel engines. You are giving some credit to the diesel that should be given to the turbo.
As covered before, diesel engines produce less power per cubic inch/centimeter. All things being equal, you need a larger turbodiesel engine to produce the same performance as a comparable turbo gas engine.
Above, I provided an example of the UK-spec 2.7 liter turbodiesel Audi A4, which produced roughly the same power and performance as does a 1.8 liter turbo gas engine. The diesel engine in that example had to be 50% larger to produce similar performance to a turbo gas engine.
Point being -- a manufacturer could probably produce a turbo gas engine of perhaps 2.5 liters or so to generate the same performance numbers as the 3.5 gas non-turbo. That 2.5L engine would invaribly get better fuel economy than its larger naturally aspirated cousin. That would make for a more accurate comparison.
Well no, you could look up the uk diesel Civic and compare it with the gasser civic!!?? I'll let you report the numbers.
OK, I did the math for you. Here's a comparison of the 2.2 liter turbodiesel (138 hp, 0-60 mph in 8.4 seconds, top speed @ 128 mph) with a 1.8 liter gas V-TECH (138 hp, 0-60 mph in 8.6 seconds, top speed @ 129 mph). The fuel economy benefit of diesel:
-City cycle: 24% -Highway: 26% -Average: 26%
That's respectable, but it falls well short of the 37% figure. Again, you need to remember that a diesel engine has to be larger to produce comparable performance to a gas engine. (And don't make direct comparisons between US MPG figures with those used in the UK -- US gallons are smaller than Imperial gallons, so you need to convert.)
And if Honda made a gas turbo with that sort of horsepower, it could perhaps generate that horsepower with a 1.4 liter gas engine. (For comparison, VW has a 1.4 liter turbo that produces 170 hp.) That would likely get better fuel economy, and further shrink the fuel economy gap between them.
Nothing sacred about 37%. From your figures, is 24-26 % better or worse? Sure, IF Honda made a gas turbo, but they don't. Trust me if Honda could get the same fuel mileage as they do with their diesel they would, they can't so they don't. As a matter of fact I did say I was all ears for a a gasser turbo that got 50 mpg. You were predictablly silent on the recommendations, but that speaks volumes.
You have people on this thread claiming that 37% is a minimum, when the difference I'm finding between gas turbos and turbodiesels with comparable output in the same cars is about 20-25%. I'm not faulting the claim that diesels are more efficient to comparable gas engines (they are), but the exaggeration being tossed about here which overstates it by large amounts.
And as for "recommendations," I don't know what you're referring to, but I haven't yet read back through everything.
Makes my gasser Civic at EPA 29/38 look like a gas guzzler!? Is 55.4 better or worse than 38 mpg (17.4 miles, 31.4% better) ?????
You're comparing US gallons for the gas engine with Imperial gallons for the diesel. And you didn't account for the benefit of the turbo given to the diesel.
Plus, the EPA measure will be different than the measurements used in the UK. You should either use UK measures for both, as I did, or else use US measures for both. If you use the UK measures and quote the MPG figures, then you also need to convert imperial gallons to US gallons. (An imperial gallon is about 20% larger, so MPG in imperial gallons will naturally be higher.)
Not totally true. The reason for the turbo on a gas engine was for more power from a smaller engine. The engine at low load low rpms will be more economical due to running closer to peak power without the help of the turbo. When more power is needed the turbo after the exhaust pressure increases will increase fuel consumption to match the power needed. A diesel doesn't need a turbo for fuel economy in the same way as a gas engine. It is primarily for more complete combustion and lower costs for less complex cylinder heads and valve trains. Look at the Honda S2000. It doesn't have a turbo but uses a more costly valve train with a high revving engine to produce great power and performance without a turbo. And its a gasser. Diesel engines are more efficient then gas engines when "not" at peak power. The gas engine has to be at peak power to be as efficient as a diesel. That is where the fuel economy advantage is realized. So when your Diesel is geared properly cruising on the highway at 1600 rpm at 62 mph the engine is not at peak power until 3600 rpm. A gas engine of say 1.0 liter running at 6000 rpm at 62 mph would be closer to its peak power but without a turbo could not get out of it's own way when accelerating. Remember peak power is peak horsepower not torque. And gas engines don't reach peak power at lower rpms. But for gas engines to be economical they need to run closer to peak horsepower. Small car tiny engine running at higher rpms. More stress on engines and less control due to narrower gear range. Yes a gas engine can be close to the fuel economy as a diesel but the trade off would be durability and still 10% less fuel economy.
You're still not seeing the point. If you have a turbo gas motor, you could use a smaller, lighter, more fuel efficient engine in place of a larger normally aspirated gas engine.
In contrast, if the diesel didn't have a turbo, its engine would need to be much larger and heavier to produce the same power.
Either way, you're talking about diesel engines often being 40-50% larger to achieve similar performance figures when compared to turbo gas motors. Compare turbo to turbo, or non-turbo to non-turbo, to get apples-to-apples results.
A "gallon" in the US is smaller than a "gallon" in the UK. Of course, you will get about 20% more MPG in the UK than you would in the US, because the "gallon" in the UK is that much larger.
We'll go back to the 2.2 liter turbodiesel to the 1.8 liter VTEC -- the turbodiesel gets 55 mpg (imperial) versus 44 mpg (imperial) for the gas engine. That's a difference of 26%, which is fine but is not 37%.
And again, if Honda had a smaller turbo gas engine, that difference would be reduced. You are giving credit to the diesel that actually belongs to the turbo.
Yes, a diesel would be a slug without a turbocharger -- it needs it to function decently.
In contrast, a gas engine runs well enough without a turbo. But it loses fuel economy that it would have if it was a smaller engine with a turbo.
When discussing the differences, don't ignore the benefit of the turbocharger. A chunk of the fuel economy gain in a diesel belongs to the turbo, not to the type of fuel used in the engine to which it is attached.
Comments
My point has been that higher performance engines tend to use more fuel, whether gas or diesel. You do realize that this fuel economy margin would shrink if you compared it to a gas engine with similarly weak performance?
You're right, of course, but one shouldn't compare Honda Fits with Bentleys and believe that we are on an even playing field here, if you know what I mean.
Here's a better comparison than the one previously offered using the 1.8T gas engine cited before. Again, this is of two Audi A4's sold in the UK: the aforementioned 1.8T gas engine, and the 2.7T diesel. They have similar specs for horsepower (161 hp for gas vs. 178 hp for diesel), 0-60 mph acceleration (8.6 vs. 8.4 seconds) and top speed (142 mph vs. 139 mph).
As expected, the diesel gets better fuel economy, in this case 22% better overall, and 19% better on a city cycle. That's fine, but that's not 37%. That's the kind of exaggeration that I'm talking about.
This example also points out the power differential between the two engine types. The turbo diesel engine has to be 50% larger to achieve similar output to the turbo gas engine. You can't compare similar displacements and get a fair comparison.
I was making this point by comparing 0-60 times. That's a common benchmark when evaluating vehicle performance, and it's fair to do this here.
Buy the diesel if you want better fuel economy or to pull loads.
I also acknowledged this -- remember my comment about semi's and locomotives. But passenger cars aren't meant to pull heavy loads, which makes that an unimportant consideration when shopping for sedans. And the fuel economy difference when comparing like vehicles is not going to be 37% -- the diesel will have better fuel economy, but it won't be quite that much. Let's have accurate data here, not exaggeration or misplaced comparisons.
Well here I don't agree. What are the numbers for the Jeep liberty CRD 2.8L and the liberty 3.7L gas engine. Vehicles same size and mass. Then use a VW jetta TDI and gas engine with about the same displacement then compare. My CRD averages 26.5 MPGs most 3.7 gassers average about 20. I had both and drove them the same. The CRD beat the EPA estimate and the Gasser never got it. But you two need to stop fighting and agree to disagree.
You're making the same mistakes that ruking is:
-You compare turbodiesels to non-turbo gas engines, while forgetting that some of the fuel economy benefit is derived from the turbo. The whole idea behind turbos is to increase peak power capacity without needing the mass that would be required to generate it with a normally aspirated engine, which improves fuel economy. Compare turbos to turbos to get apples-to-apples.
-You forget that higher output engines tend to have lower fuel economy, no matter what. A powerful gas engine uses more fuel than does a less powerful gas engine. A more powerful diesel will use more fuel than will a less powerful diesel.
This stuff is all pretty basic, folks. If you want to compare weak engines and strong engines, then don't be surprised that the weaker motors use less fuel. This is just how internal combustion works -- you can't produce power without consuming energy.
Don't twist my words. It's all in the gearing!! And diesels accelerate better in residential driving due to quicker shifting from stop sign to stop sign. You don't have to drive as aggressively as a gasser. Its more pleasurable. You need to drive a diesel to know the difference in driving characteristics between the two. A gasser feels like your winding up a loose rubber band. The diesel goes right into gear and pulls without letting up till you let it. I like the diesel better for everyday driving. I prefer a corvette if I want to feel the engine work and work myself driving it.
I would agree. I actually wish I had a tad more power and VW oem would have put a 6 speed manual, as another poster had mentioned about the Skoda. That trans I know is far beefier than mine, even as I know the 5 speed that came with mine can with reasonable care go 400 to 500k.
Come now, I just spent the last several posts showing how obviously flawed this statement was. If you guys want to compare low output engines to high output ones, then you're well off track.
Diesel cycle efficiencies are about 40%. So 40-25=15, 15/25=60% improvement over a gasser. Diesel also has 10% more energy per gallon then gas so 37% better fuel economy is not unrealistic.
But it must be noted that a gas engine running at peak power is just as efficient as a diesel. But only at peak power. So in the real everyday world diesels get about 37% better mpgs then gassers!!!!!!!!!!!
it's also semi-funny to see people arguing whether it's torque or horsepower which is more important to acceleration, or whether it's "all in the gearing". observing engine torque curves and comparing with dyno output graphs can be interesting - look what happens at the shift points - look how the gearing affects the dyno output at various rpms.
That made me think a little bit about:
How much more efficient REALLY is diesel?
So I found this article:
Is Diesel Performance Superior Overall Compared to Gasoline Power?
1. Does not take into account that all new diesel powered vehicles will have PM traps.
2. Article does not take into account that S15 diesel fuel is now the norm.
3. Article does not mention the use of biodiesel and that fewer pollutants are produced when this fuel is used.
4. Article ignores the fact that there many other sources that show that it is far more energy intensive to make ethanol than biodiesel.
5. Date of article is April 2005. Lots of things have changed since then.
Of course, the biggie three have been in it for a long time GM, Ford, Dodge, but in the bigger light truck market.
When you compare/contrast this with the "dip the toe in the water" progress with the hybrid, it is even more remarkable.
If one uses the Liberty diesel as an example, I am sure the oem wished it had 2x the products of 11,000 that it produced in that first year, to sell.
VW in 2003 had 4% of their products diesel. I also think they probably could have sold 2x or eight percent of their product line. They surely NOW sell every diesel, even before it hits the lot.
I also think a lot of the changes has to do with the increases in the R and D dollars and commitment to invest to the diesel segment. It would not be too financially good to put HUGE percentages of R and D money to a declining market segment, either to lack of interest or regulatory efforts at diesel extinction. People are increasingly recognizing the utility of being ABLE to use an alternative fuel. One imediate pay off's is the much better mpg on like models. In the case of the 2003 VW Jetta, 37%.
There has been a news item that Iran could possibly run out of oil in 2015. It is good that folks are realizing they can vote with their dollars, even as Iran and others are cutting back their production to firm up sagging prices. Another interesting news item was the -54 AVERAGE mileage from 2004 to 2005. While this is FAR less than one half of one percent, .0039384, it is evidently having a Tsunami effect. Imagine what a 37% FUEL DECREASE would do!!
"Making a gallon of diesel fuel requires 25% more oil and emits 17% more heat-trapping greenhouse gases than gasoline reformulated with MTBE. Similarly, diesel requires 17% more oil and emits 18% more heat-trapping gases than gasoline reformulated with ethanol. This means that diesel fuel's advantages from its higher per-gallon energy content and better performance on greenhouse gases are partially offset by the impact of diesel's fuel-production process."
and:
The improved efficiency of diesel engines can also help reduce oil consumption. It should be noted, however, that it takes about 25% more oil to make a gallon of diesel fuel than a gallon of gasoline, so we should really look at how a vehicle does on fuel efficiency in terms of "oil equivalents." Thus, we need to adjust the mileage claims for diesel vehicles downward by about 20% when comparing them to gasoline-powered vehicles.
So with that in mind, Ruking1's 37% is not an effective number. The 37% might apply ONLY to the VW TDI vs gasser example he is presenting, and that could very well just have to do with the higher gearing that VW sets.
E350 Mercedes
EPA 19/26 MPG 272 hp and 259 Torque 0-60 in 6.9 seconds
Weight 3740
Max HP @ 6000 Rpms
Max Torque @ 2400 rpms
E320 Bluetec
EPA 26/37 MPG 208 HP and 388 torque 0-60 in 6.6 seconds Torque wins in the acceleration game.
weight 3860 lbs
max HP @ 3800 rpms
max Torque @ 1,600 rpms
These are basicly the exact same car just one with gas and one with diesel and one with gas.
Well no, you could look up the uk diesel Civic and compare it with the gasser civic!!?? I'll let you report the numbers.
.
I was just about to ... now I'm saved.
I also want to add, however, the Audi diesel racecar that won LeMans recently. Obviously as good or better than all the gassers, given it won. AND more efficient, allowing it to refuel less often.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
I was inspired by Larsb's post on that DIESEL super sports car that gets 48 mpg on the race track and 70 mpg on freeway at 62? mph!!! Got to love that twin turbo diesel BEAST !!!
It's not the diesel engine or the diesel fuel that makes the 37% number.
It's the GEARING that the manufacturer uses that determines the extra "efficiency" of the diesel version of the car.
We got any of those trolling around here? :shades:
But as gearing being germane to the discussion, I have posted prior that I wish we had the increased power and gearing that say the European available Skoda (do a search for alltorque's posting on the Skoda). Specifically 130 hp/229 # ft of torque vs 90 hp/155# ft of torque and the 6th speed vs the 5 speed. My SWAG is if I didn't put my right foot into it, the MPG would INCREASE at worse 1 mpg to 4 mpg and that is with SIGNIFICANTLY more hp and TORQUE !! The two edged side in effect it would double as a PERFORMANCE machine. Again the right foot is the lead switch to turn on and or off. Whereas now it is really a good road to economy car. So one consequence is an even better mpg car is banned from the USA!! I really would not mind the mpg range being extendded 1-4 mpg.
Well no, you could look up the uk diesel Civic and compare it with the gasser civic!!?? I'll let you report the numbers.
..."And good job you want to, as only a buffoon would touch the 1.6 and 1.8-litre petrol alternatives here when faced with such an excellent choice. It's Honda's 140bhp 2.2-litre unit, as used to such wonderful effect in the larger Accord. The paperwork records a top speed of a notch under 130mph and a 62mph sprint of just over eight seconds, but bear in mind that this engine develops nearly twice the torque at half the revs (ie, 251lb ft at 2,000rpm) of the 140bhp 1.8-litre petrol alternative and you begin to get an idea of its superiority."...
..."and intervals at 12,500 miles, this is a reasonable proposition, while the overall 55.4mpg return is very impressive for the class, suggesting a mid-40s fuel consumption in the average mix of driving is feasible...
http://www.tiscali.co.uk/motoring/diesel/diesel-new-honda-civic/2
Makes my gasser Civic at EPA 29/38 look like a gas guzzler!?
Must be all in the gearing?
2013 LX 570 2016 LS 460
2013 LX 570 2016 LS 460
From the DOE..
What does a barrel of oil produce?
If I read the other searches correctly gasoline being the most volatile component of a barrel of oil is separated first and in the greatest volume ( I'm open to being corrected here ) at the least cost!!
19.6 gal of Gasoline per bbl
10.0 gal of Diesel/Fuel Oil per bbl
Now another question arises. Our dependency on dino fuel?
Let's take two hypothetical vehicles
.. Jetta TDI getting on average 40 mpg
.. Corolla getting on average 30 mpg
The Jetta TDI is 33% more efficient than the gasser Corolla. For a normal drive of 15000 mi/yr the respective fuel consumptions would be..
.. Jetta 375 gal
.. Corolla 500 gal
But one barrel of oil produces 19.7 gal of gasoline and 10 gal of diesel fuel. So to supply the Corolla's 500 gal usage it takes 25.5 bbl of oil. These 25.5 bbl also produce 255 gal of diesel. But wait the Jetta needs 375 gal to go 15000 miles. That means that an additional 12 bbl of oil are needed to be processed in order to produce the shortfall that the Jetta needs.
So one Corolla using 500 gal/yr needs 25.5 bbl of oil but the Jetta using 375 gal/yr needs 37.5 bbl of oil?
So diesel is more expensive to produce (?) because more of the base product is needed for the same distance driven because the yield per bbl is lower. That 25% extra base product seems to cancel the 35-40% gain in efficiency of the diesel engine.
But then the pricing is skewed. Diesel is 'only' $.20-$.60 higher in cost than Reg Unleaded. That's not 25%. Ergo
The oil companies are subsidzing the diesel users? :surprise: Sure
The oil companies are overcharging the more in demand gasoline users?
Now when you ADD to that, that unleaded regular is processed from the LSC or light sweet crude which is the price MOST often quoted when they ask daily : what is the price of a barrel of oil? Keep in mind that even refining light sweet crude has as a natural consequence the app DOE 23.81% of #2 diesel fuel. Light sweet crude is MUCH less plentiful than other than light sweet crude and is MORE costly. OTLSC (OTHER THAN) is actually the majority of the barrels of oil pumped from the earth. The upshot is it sells on the open market 30-40% CHEAPER than LSC !!!!!!!!! So as you can probably deduce, because #2 diesel is fungible, the cost is so called "artificially" higher since 23.81% of LSC is diesel processed from the higher priced LSC. So again because #2 diesel is fungible, the oil companies most assuredly sell diesel process from OTLSC for a higher price rather than a lower price because of the fungibility issue. Indeed those types of commodies are openly traded in commodities exchanges such as CBOT etc etc. Of course all have heard of OPEC and its price setting for a barrel of oil. In addition both products gas and diesel are pipelined co mingled and separated out at the end destination terminal, which again incurs host of process and separation fees/cost.
http://science.howstuffworks.com/oil-refining2.htm
Refining Processes
The Modern Refinery
Blending
About Hydrocarbons
Other Compounds
Diesel Fuel Chemistry
Chemisty of Diesel Fuel Instability
Biodiesel
Diesel fuel is made from petroleum. All petroleum crude oils are composed primarily of hydrocarbons of the paraffinic, naphthenic, and aromatic classes. Each class contains a very broad range of molecular weights.
As it comes out of the ground, crude oil can be as thin and light-colored as apple cider or as thick and black as melted tar. Thin crude oils have relatively low densities and thus high API gravities (see below). Therefore, they are called high-gravity crude oils; conversely, thick crude oils with relatively high densities are low-gravity crude oils.
DENSITY AND GRAVITY
Density () is the mass of a unit volume of material at a selected temperature. For example, the density of water is 0.9990 grams per cubic centimeter (g/cm3) at 60°F (15.67°C). Relative density (RD) – also called specific gravity – is the ratio of the density of the material at a selected temperature to the density of a reference material at a selected temperature. For the relative density of petroleum crudes and products in the U.S., the reference material is water and both temperatures are 60°F.
RD (60 / 60°F) = sample (60°F)
–––––––––––––
water (60°F)
The United States petroleum industry often uses API gravity instead of relative density. The following equation relates API gravity, in degrees API (°API), to relative density.
°API = 141.5 – 131.5
––––––––––––
RD (60 / 60°F)
While API gravity measurements may be made on liquids at temperatures other than 60°F, the results are always converted to the values at 60°F, the standard temperature.
API gravity is an arbitrary scale developed by the American Petroleum Institute in the early years of the petroleum industry. Density had been used as a primary indicator of quality for liquid products. However the higher value products have lower densities. The API gravity scale was constructed so that API gravity increases inversely to density; therefore, higher value products have higher API gravities. And while the densities of most petroleum products are less than one, the API gravity scale also was constructed so that most values are between 10 and 70.
Refining is the process of converting crude oil into high value products. The most important are transportation fuels – gasoline, jet fuel, and diesel fuel. Other important products include liquefied petroleum gas (LPG), heating fuel, lubricating oil, wax, and asphalt. High-gravity crude oils contain more of the lighter products such as gasoline and generally have lower sulfur and nitrogen contents, which makes them easier to refine. However, modern refining processes are capable of turning low-gravity crude oils into high value products. Refining low-gravity crude oils requires more complex and expensive processing equipment, more processing steps, and more energy and, therefore, costs more. The price difference between high-gravity and low-gravity crude oils reflects the refining cost difference.
So the low grade crude which according to you makes up most of the feedstock for diesel is priced significantly lower than LSC, which by Chevron's implication ( above ) is a result of the higher costs of processing meaning that the net result is approximately the same.
So this still creates the situation that more feedstock oil is needed to derive the 375 gal of diesel needed to power the Jetta. Thus the UCS's estimate of a 20% reducing factor for diesel still seems reasonable. However throw in some locally made biofuel ( 120 gal/yr ) and no additional dino fuel is needed.
The costs are relative to many factors. With less light crudes available gasolene will become more expensive due to lower supply. Diesel can be had from much heaver crude while the amount of gasolene will decrease.
It's a better comparison than most. However, you are still comparing a turbocharged diesel to a non-turbo gas engine car.
The diesel fans in the forum seem to forget that turbocharging provides fuel economy improvements to both gas and diesel engines. You are giving some credit to the diesel that should be given to the turbo.
As covered before, diesel engines produce less power per cubic inch/centimeter. All things being equal, you need a larger turbodiesel engine to produce the same performance as a comparable turbo gas engine.
Above, I provided an example of the UK-spec 2.7 liter turbodiesel Audi A4, which produced roughly the same power and performance as does a 1.8 liter turbo gas engine. The diesel engine in that example had to be 50% larger to produce similar performance to a turbo gas engine.
Point being -- a manufacturer could probably produce a turbo gas engine of perhaps 2.5 liters or so to generate the same performance numbers as the 3.5 gas non-turbo. That 2.5L engine would invaribly get better fuel economy than its larger naturally aspirated cousin. That would make for a more accurate comparison.
OK, I did the math for you. Here's a comparison of the 2.2 liter turbodiesel (138 hp, 0-60 mph in 8.4 seconds, top speed @ 128 mph) with a 1.8 liter gas V-TECH (138 hp, 0-60 mph in 8.6 seconds, top speed @ 129 mph). The fuel economy benefit of diesel:
-City cycle: 24%
-Highway: 26%
-Average: 26%
That's respectable, but it falls well short of the 37% figure. Again, you need to remember that a diesel engine has to be larger to produce comparable performance to a gas engine. (And don't make direct comparisons between US MPG figures with those used in the UK -- US gallons are smaller than Imperial gallons, so you need to convert.)
And if Honda made a gas turbo with that sort of horsepower, it could perhaps generate that horsepower with a 1.4 liter gas engine. (For comparison, VW has a 1.4 liter turbo that produces 170 hp.) That would likely get better fuel economy, and further shrink the fuel economy gap between them.
You have people on this thread claiming that 37% is a minimum, when the difference I'm finding between gas turbos and turbodiesels with comparable output in the same cars is about 20-25%. I'm not faulting the claim that diesels are more efficient to comparable gas engines (they are), but the exaggeration being tossed about here which overstates it by large amounts.
And as for "recommendations," I don't know what you're referring to, but I haven't yet read back through everything.
You're comparing US gallons for the gas engine with Imperial gallons for the diesel. And you didn't account for the benefit of the turbo given to the diesel.
Plus, the EPA measure will be different than the measurements used in the UK. You should either use UK measures for both, as I did, or else use US measures for both. If you use the UK measures and quote the MPG figures, then you also need to convert imperial gallons to US gallons. (An imperial gallon is about 20% larger, so MPG in imperial gallons will naturally be higher.)
In contrast, if the diesel didn't have a turbo, its engine would need to be much larger and heavier to produce the same power.
Either way, you're talking about diesel engines often being 40-50% larger to achieve similar performance figures when compared to turbo gas motors. Compare turbo to turbo, or non-turbo to non-turbo, to get apples-to-apples results.
A "gallon" in the US is smaller than a "gallon" in the UK. Of course, you will get about 20% more MPG in the UK than you would in the US, because the "gallon" in the UK is that much larger.
We'll go back to the 2.2 liter turbodiesel to the 1.8 liter VTEC -- the turbodiesel gets 55 mpg (imperial) versus 44 mpg (imperial) for the gas engine. That's a difference of 26%, which is fine but is not 37%.
And again, if Honda had a smaller turbo gas engine, that difference would be reduced. You are giving credit to the diesel that actually belongs to the turbo.
In contrast, if the diesel didn't have a turbo, its engine would need to be much larger and heavier to produce the same power. "
If you have a turbo diesel motor, you could use a smaller ligher, more fuel efficient engine in place of a larger normally aspirated engine.
Might be why a turbo diesel motor is used.
In contrast, a gas engine runs well enough without a turbo. But it loses fuel economy that it would have if it was a smaller engine with a turbo.
When discussing the differences, don't ignore the benefit of the turbocharger. A chunk of the fuel economy gain in a diesel belongs to the turbo, not to the type of fuel used in the engine to which it is attached.