two question, really:
1. What happened to the price of diesel fuel in the US about 2 years ago?..it was always cheaper than gasoline until problems were announced related to refinery fires and a shift in production…price has never reverted while diesel fuel remains cheaper than gasoline in Europe.
2. Europe is loaded with diesel vehicles (about half of cars on the road) due to better economy and environmental factors. Why can’t auto companies produce diesel cars for the US?
The reason diesel engines get better fuel mileage then gas engines, is do mainly in part that diesel can burn at a lot leaner fuel to air ratio. Unfortunately lean burning causes high Nitrous Of Oxide emissions that don’t meet the new strict US emission standers. Running a diesel engine at stoichiometric to lower NOX emissions takes most of the fuel savings away. So I have herd.
Actually, state-of-the-art emissions controls can get diesels to burn cleaner than gasoline cars, but it requires the use of ultra-low sulfur diesel to work. European standards have mandated it for a while, but the trucking industry has lobbied to prevent mandating it here until recently. Many manufacturers overseas were unwilling to change their designs to handle the higher standard of sulfur in the diesel fuel here. The extra cost of diesel is due to the mandated extra refining to get to ultra-low sulfur standards. Also, diesel trucks and cars are soon to be required to meet much stricter emission standards. But, this will allow more diesel cars into the market, as the european manufacturers are already making cars that will meet the standard. They just needed the ultra-low sulfur diesel standard in place before sending cars here.
On a side note, fuel price in Europe is not really an even comparison to prices here because of the incredible difference in tax structure. OTR Fuel taxes in Europe are a lot higher, and structured by type to the point where the manufacturing cost is lost under the burden.
Diesel prices don’t fluctuate as much as gas prices. When gas prices stabalize you’ll see Diesel prices about 20-30 cents cheaper then regular unleaded. It’s happened EVERY TIME in the past 30 years. Just this past spring Diesel was about 20 cents a gallon CHEAPER then unleaded here in NH.
Excellent reply; European fuel prices are designed by governments to favor diesels, and manufacturing costs are a minor fraction of the total. Since the US trucking industry has now been legislated into using Ultra Low Diesel Fuel (ULDF), we will see many more car diesels on the road in the future, as European and Japnese car companies already have these in production.
Since a diesel engine gets more energy out of a gallon of fuel, this fact will drive the increased usage, but I doubt the US government will start manupulating the selling price with differential taxes the way they have in Europe. My guess is that, unlike ethanol and biodiesel, there will be no tax breaks for ULSD, and the price will find its own level. The new diesel costs more to produce, while gasoline production costs have remained level.
As per Americar’s post, diesels are efficient because of the very high compression ratio and the high heat content per volume of diesel fuel. Excess air is needed to make sure all the fuel burns. It does not increase efficiency by itself. The best situation is to make sure all the fuel burns and to take care of excess NOX produced with catalytic converters. In 2 cycle diesels the excess air acts as a scavenger to clear the conbustion chamber. Cleaning up a 2 cycle engine, gas or diesel, is difficult.
Now that we have new CAFE standards for the future, and ULDF, you will see many more diesels coming in. Most development has already been done overseas, so GM, Ford and Chrysler will source their overseas partners or subsidiaries. Honda, Nissan, Toyota and Mazda all have small diesels in production overseas.
It’s true that diesels always combust in excess air, however, that is not why they offer better fuel efficiency.
Most of the efficiency gains come from higher compression ratios and the fact the diesel fuel has a higher specific energy than gasoline.
Gasoline (regular) - 125,000 BTU/gal
Diesel - 139,000 BTU/gal
Compression ratios for diesels are typically around 16 ? 25:1 where gasoline engines are usually no higher than 11:1.
“As per Americar’s post, diesels are efficient because of the very high compression ratio and the high heat content per volume of diesel fuel. Excess air is needed to make sure all the fuel burns. It does not increase efficiency by itself. The best situation is to make sure all the fuel burns and to take care of excess NOX produced with catalytic converters. In 2 cycle diesels the excess air acts as a scavenger to clear the combustion chamber. Cleaning up a 2 cycle engine, gas or diesel, is difficult”.
Regardless, its the ability of diesel to burn at such a lean mixture that makes it possible. Does not a diesel always run at WOT because there is not ONE? And its strictly the amount of fuel being injected into the engine that controls engine speed. This makes the fuel air mixture all over the board. (Maybe modern day diesel Engine management systems have refined the A/F process, but thats how I remember it to be.)
A quick Google search suggest emission equipment to control NOX on diesels to be complicated and expensive. This could limit Diesels to only expensive vehicles.
Secondly, if it was based on BTU content alone as stated.
“Gasoline (regular) - 125,000 BTU/gal
Diesel - 139,000 BTU/gal”
there would only be small fuel mileage gain with diesels. Less then 10% about 2 to 4 MPG at best.
I am standing by my original post.
Regards
“Regardless, its the ability of diesel to burn at such a lean mixture that makes it possible. Does not a diesel always run at WOT because there is not ONE? And its strictly the amount of fuel being injected into the engine that controls engine speed. This makes the fuel air mixture all over the board.”
You are correct, diesels are controlled by fuel only and always have considerable excess air available. Part (but not all) of the increase in efficiency is due to the lack of a throttle and the lack of manifold vacuum (the engine does not have to overcome vacuum during the intake stroke). The combination of excess air and high combustion temperatures is responsible for the higher NOX emissions. Reduction of the combustion temperature would adversely affect the efficiency. It really doesn’t make much sense to talk about rich or lean diesel mixtures.
You are correct, the pollution control systems required to meet current standards for NOX (and particulate) are complex and expensive. There will be a significant cost difference between similar gasoline and diesel vehicles unless the manufacturers manipulate the prices. This is the benz bluetec system:
http://www.mbusa.com/campaigns/alternative-fuels/index.do
It’s interesting that their prices for the E350 (gasoline) and E320 (diesel) are only $1000 different, which makes me wonder if they are playing around with the pricing to increase diesel sales.
As per previous posts, the diesel does not rely on its large amount of excess air to gain efficiency; that is mostly the result of the very high compression ratio compared to gas engines. High combustion chamber temperatures favor high efficiency, but produce NOX. This problem is solved in gas engines and boilers by Exhaust Gas Recirculation (EGR), which in turn has a somewhat negative affect on efficiency. So, all engines are thermodynamic and environmental compromises!
Cleaning up commercial diesels comes at a significant cost to operators. Howver, these are choices society has to make. City busses in the future may run on natural gas, since they can be made to burn very clean without major engine add-ns. Many cities are already experimenting with gas conversions.
With respect to the price of diesel options, both Mercedes and Volkswagen years ago did not charge extra for diesels. With the Blue Tech, howver, I’m sure Mercedes is subsidizing this model, at least initially, since it has much lower tailpipe CO2 emissions, thus allowing them to meet the Euro standards. Keeping the Smart car also helps their corporate averhge significantly.
A number of factors went into the price changes. World demand for diesel is up, there were some refinery issues in the US and we switched from LSD to ULSD which does cost a little more, but far less than the price has gone up. I suspect part of it is simple profit taking on the part of the oil companies. Does that surprise you? Even the rush to alcohol fuel is causing a price increase as the farmer’s burn up diesel in their tractors to make the corn that is turned into alcohol.
My prediction is that there will not be a reduction of diesel prices any time soon, but I do expect gasoline prices to go up faster than diesel.
For ages, since the automobile became the mainstay of US transportation, gasoline has been the main money earner, and diesel was sort of the ugly sister. This is changing rapidly for economy reasons, as well as the requirement that all fuel distributors must have ULSD.
Total US refining capacity is not really rising; most growth in demand has been met by imports. ULSD will be the glamor fuel of the furtur. Up to now, diesel has not suffered from seasonal fluctuations, but that will change as it becomes a mainstream motor fuel.
Americar, you seem not to understand that diesel efficiency is a direct result of the compression ratio, as it is with an Otto (spark ingnition) engine. This formula can be found in every thermodynamics text! We can increase the power output of both gas and diesel engines by turbo charging to get more fuel and air through the engine. Diesels need excess air to get rid of the soot that results from incomplete combustion. It is true that the output of a diesel is related to the amount to fuel you introduce. That is equally true of an direct-injected gas engine.
So, a diesel with a 17:1 compression ratio compared to a gas engine with a 9:1 ratio would be 17/9x100=189% or 89% more efficient in theory. If we add your 139,000/125,000x100=111.2% or 11% more energy per gallon, we would theoretically get 89+11=100% better mileage with a diesel. In real life it is a little less because of pumping losses and other parasitic items. Again, this has NOTHING TO DO WITH EXCESS AIR. Both gas and diesel engines need some excess air to meet the EPA particulate and unburned hydrocarbon standards.
I agree that controlling a diesel to be squeaky clean is expensive and results in some loss of efficiency. Maintenance costs will rise as well, reducing the prior advantage of simplicity. Car owners won’t be able to work on their diesels on the weekend due to the complexity.
I remember comparing the efficiency of diesels vs gas engines back in my internal combustions course (34 years ago). I forget many of the details, but two things I do remember are:
1: The throttle plate does create pumping losses in a gas engine. These losses were not insignificant.
2: Due to the vacuum caused by the throttle plate, a gas engine running at partial throttle often must have the piston travel a good deal up the power stroke before the pressure in the combustion chamber even reaches atmospheric (14.7 psi). That means the effective compression ratio at partial throttle is very low - and as a result the efficiency of a gas engine at part-throttle is lowered as well.
“With respect to the price of diesel options, both Mercedes and Volkswagen years ago did not charge extra for diesels. With the Blue Tech, howver, I’m sure Mercedes is subsidizing this model, at least initially, since it has much lower tailpipe CO2 emissions, thus allowing them to meet the Euro standards. Keeping the Smart car also helps their corporate averhge significantly.”
Yup, the old diesels are significantly less complex than the equivalent gassers, and they had essentially no pollution controls (mine has nothing except a EGR and a crankcase vent return), even in the 80s when gas engines were a real mess. The new ones must cost more to manufacture, they must be discounting them for the U.S. market to get a good foothold (and to drive up the fleet mileage average). Now all we need is the diesel version of the smart certified in the U.S. (I don’t know if that’s practical).
Thank for all comments.
I had not considered the government manipulation of fuel costs in Europe, which I’m sure takes place at the higher prices for all fuels here. If ULSD is needed to protect the environment, that is probably a lesser societal investment than Hydrogen or other exotic fuel infrastructure.
The observation on the street in Germany is that: 1) Europeans love diesels; 2) they drive them; 3) the cars don’t smoke - can’t comment on NOX, but; 4) Europeans are much more zealous about the environment than I’ve ever detected in the States; 5) all ranges of cars are equipped with diesels.
It will be a good day for all when more diesels are available in the US. When I’m back there my (recent) big Ford pick-up gets better mileage on bio-diesel than my previous Isuzu Amigo.
The technology to burn ULSD may be more complex than an old diesel, but I am concerned about how hybrids will run after 3-5 years and how much maintenance they will require.
“The technology to burn ULSD may be more complex than an old diesel, but I am concerned about how hybrids will run after 3-5 years and how much maintenance they will require.”
You’re not the only one who is thinking about this issue!
I am convinced that hybrids, or at least the current version of them, are merely transitional vehicles until something better comes along and that they will not be on the scene long-term.
As most of us are now aware, unless a hybrid is used for mostly urban driving, its economy advantage is not sufficient to amortize the extra cost of the hybrid system in less than a decade (if not more). A hybrid that can be plugged into the electrical grid is more practical, and we may see those within a year or so, but I expect that they might be even more expensive than the current version of hybrids.
Right now, and for some time to come, a fuel-efficient gasoline engine car like a Fit or a Versa is more economical in the long-run for the typical driver. However, once the new Blue Tech technology diesels are widely available in most brands of cars, I believe that the public will see the wisdom of going with that technology.
I recently read that the new Blue Tech diesel Accords sold in Europe were averaging something like 52 mpg, so unless the price of these vehicles became truly prohibitive, a Blue Tech diesel car would seem to be much more practical for the average driver than a hybrid would be–especially when you consider the purchase price and the eventual cost of battery replacment on the hybrids.
I am looking forward to getting a diesel vehicle the next time that I buy a car, which should be in approximately 2-3 years.
I guess it depends where you live. Diesel is more expensive than gasoline in the mid-Atlantic area. It’s about 30 cents more than regular, but still saves money due to the better mileage.
There is an excellent article about diesels in Popular Mechanics this month:
http://www.popularmechanics.com/automotive/new_cars/4237945.html?series=19
The article is just a condensed intro to the topic, but it’s a good start.
One concern I have is the “Blue Tech” system – apparently, it squirts a proprietary urea solution (urea? like, you know, pee?) into the exhaust to neutralize NOX and such.
I’m just wondering what it’s like to live with this Blue Tech solution. How much does it cost, how often do you need to fill it up, does it freeze, can you get it at your local Wal-Mart or auto store, what happens when the injector clogs, does the exhaust smell like urine, etc…?
We already have several other fluids to worry about – if there’s one more, it will be a real problem for a lot of people.
There are actually two different generations of bluetec, the current version (not 50 state certified) does not include urea injection. The next generation (which will be 50 state compliant) does include urea injection. My understanding is that this “canister” will be a dealer service item that will have to be replaced during routine service every 20,000 km, or so, no idea how much it will affect the cost of service.
BTW, the use of ammonia to reduce NOX is not new in commercial applications, it’s been used for decades.
I read (in Business Week, perhaps?) that the Blue Tech system that utilizes urea is the Mercedes-Benz system and that Honda has a competing Blue Tech system that does not utilize urea.
My guess is that Honda is confident of having their non-urea system approved for 50 state use. If so, that would be a whole lot more convenient. And, of course, we all know about people who don’t have certain maintenance items taken care of on their cars, so in the long run, the non-urea system would be better for everyone–IMHO.