Gasoline vs. Diesel

So, I was looking at the new Golfs down at my local VW dealership the other month. While I’d like to buy one someday, I was really just there to take a test drive so I could get the free CD of songs from VW ads (and that one from the wedding one isn’t on it, consarn it!). My reasons for liking the Golf are two-fold: I’m tall, and it fits me better than most cars, and it gets pretty good mileage. My question is, while the TDI diesel engine gets something outrageous like 45 mpg compared to the gas version’s 29, it has substantially more emissions. So, what’s the better choicce ecologically? Granted, I’ll spend less on fuel for the TDI, but should the increased pollution keep me awake at night?

I think first we need to find out exactly how much more emissions “substantially more” is. The diesel offers 55% better fuel economy than the available gasoline engine. does diesel produce 55% more harmful emissions per gallon? Are some emissions more harmful than others?

Also, which fuel creates more pollution just getting it to the gas pumps? I hear gasoline is highly refined, while diesel takes relatively little processing.

And which engine took more resources to manufacture?

If you really want to look hard at the issue, you need to look at the whole supply chain, from digging the oil out of the ground to motoring down to the 7-11.

Lets say you are driving home from some road trip on some back road. Fuel gague is below E and you see a gas station comming up do you say.
1 - thank God - looks like they’re open.
2 - looks like they’re open, I hope they got diesel.

AFAIK, the VW diesel is by far the cleanest diesel on the market,
sporting both electronic fuel injection and catalytic converters.

Being a much heavier fuel than gasoline, diesel fuel generally
has more carbon per unit of volume, and thus puts out
proportionately more hydrocarbons and soot than gas.

But this generally happens at or near wide open throttle; at part
throttle the engine is running lean, so practically all the fuel is
converted completely into carbon dioxide and water vapor.

According to this article (which I just found doing a web search, so it’s nothing special) says these produce 500ppm sulfur emissions compared to gasoline average of 300ppm.

However, I believe this is only in the US - diesel fuel sold in europe contains much less sulfur, contributing to the popularity of diesel cars there. I can’t remember off hand why low-sulfur diesel is not available in the US, anybody?

Just to give you some numbers, I had my 1999½ New Golf GL TDI emissions tested a couple different times. Here are the data from both tests, with expected/acceptable range in parentheses:

mileage: ··················5000·······28000
HC ···(0-400ppm)·········8·············6
CO ···(.2-1.5%) ··········0.2 ········0.01
CO[sub]2[/sub] ··(14-15%)··········3.7············†
O[sub]2[/sub] ···(.2-1.5%)············‡·············‡
NO[sub]x[/sub] ··(0-400ppm)·······272··········116

† not measured second year
‡ too low to measure

Sorry, sulfur wasn’t part of the test. The expected ranges are of course for gasoline engines, and the testers really weren’t sure what to make of the results for the diesel.

A perhaps debatable answer to your question comes from the Environmental Protection Agency. They rank vehicle emissions according to “pounds of smog-forming pollution per 15000 miles.” By that criterion, the diesel Golf is substantially worse than the gasoline version.

All good points to consider. As for how much more ‘substantially more’ is, I can’t remember, other than it was a lot more. Hmm, maybe I’ll see what I can find and get back to yous guys.

If you live where it gets cold, there’s one more thing to deal with. On a really cold day, the fuel thickens to the point where the engine won’t run. You can fight it by carefully mixing alcohol with the fuel, but that’s a hassle you might not want to deal with when your fingers are freezing. You can park in a garage or use a block heater, but the grocery store won’t have a plugin for you.

I live in the comfortable climes of the San Francisco Bay Area, so the cold won’t be too much of a problem. C’mon, should Anthracite be in here by now? Maybe if they had a coal burning VW.

I have heard this is a big problem with diesels, but as it concerns my current VW Golf, it hasn’t been an issue. The glow plugs seem to do the trick, and this has been tested on my car down to about -10°F (-23°C).

Other concerns I’ve heard about diesels, and my experience with the Golf:[ul][li]Noise - Not really noticeable inside the car, a bit noisy on the outside, but definitely less than other diesel engines.[/li][li]Smell - Even less of an issue than the smell of unleaded in my old Honda. However, sometimes the pump area at the station is a little greasy.[/li][li]Slow acceleration from stop - Not a problem; apparently the turbo injection solves this.[/li][li]Difficulty finding stations - You may want to check around before you buy. Not an issue for me, since there are plenty of interstates and various fleets of diesel vehicles nearby. Some places, I’ve had trouble finding a station. On the plus side, when the low fuel light beeps to notify you of only 7 liters in the tank, you get 80 or 90 miles to seek one out.[/ul]I don’t want to give an unqualified endorsement; I have had some problems, but so far as I can tell they are unrelated to the fact that my car happens to be diesel.[/li]
A couple other points:
There has been talk in the EPA (the mighty tail wagging the dog of the Bush administration, don’t ya know) of raising taxes on diesel fuel, or requiring it to be cleaner, in the next several years. This could increase the cost of operation, although by how much is anyone’s guess.

There is a tendency for stations to list “Diesel” on their signs, but not list the price. Caveat emptor. Compared with unleaded gasoline, diesel prices go down in the summer - at or below the lowest unleaded - and up in the winter - usually around the price of the premium unleaded. I assume this is due to increased demand for unleaded during the summer vacation months, and increased demand for heating oil in the winter.

I apologize, I’ve had to deal with a criminal who is banned from my board who is accessing it illegally. Now that I’ve turned the issue over to my new assistant Rose (who should be registering over here in a bit…I’ll have to post a welcome thread!), I can relax now and focus on the fun things, while she does the legal things.

Anyhow. What are the real emissions you need to focus on? I mean, focusing on NO[sub]x[/sub], SO[sub]2[/sub], ozone, HC, soot, and all that is nice. And you can argue a “tragedy of the commons” for each effect. But what should you really be most concerned about, if you have to pick one emission to judge how friendly your car is?

My guess is simply CO2. Or, to be more general about it, overall fuel efficiency. Ignoring the effects of thousands of people making your same decision, the thing to focus on, from an environmental standpoint, is how much of a limited resource you are using, and how much carbon you are adding. Now - wait a minute Una, you might say, doesn’t carbon (CO2) fall under the same problem as the NO[sub]x[/sub], SO[sub]2[/sub], ozone, HC, and soot? Aren’t they all a cumulative effect?

My answer is yes, but all of the above pollutants are already limited by law or by design in some manner. Except the CO2 emissions, which are only limited by you and your choices. So I say, from a strictly environmental stance, once could argue that you are at least going with the what the law regulates you to, plus you may be putting out less CO2 overall, and using less of the fuel resources overall.

I guess to round out what I’m saying - I don’t think there is a clear, scientific choice that can be made that tells you absolutely one way or another. One could also argue that our regulations on diesel emissions are too lenient, and they would probably be correct. Diesel emissions, according to a friend who came from the DoE, have not been limited as much as they should for two reasons:

  1. Trucker’s unions.
  2. Various environmental movements wanting to encourage diesel car production and use.

If you think about which party is most closely associated with unions and environmentalists…you can see where is opinion is heading.

There you go. :slight_smile: …If you really want to stop pollution… Buy a bike. Second-hand.

I noticed that they even specify anthracite coal too! :slight_smile:
Great link!

Diesel fuel prices go up during the winter becase diesel and home fuel oil are basically the same thing. Law of supply and demand.

I haven’t noticed the price variations between seasons because I don’t drive a diesel, but when I have noticed prices diesel always seems to be around the price of premium gasoline.

I doubt that it was four wheel drive. The German analog to the American jeep was the Kubelwagen (re-introduced in the 1970s as the VW Thing). It was rear-wheel drive only, but was so light that it could easily be manhandled if it got stuck.

Back to diesel, aircraft engine manufacturers are developing diesel engines for light aircraft. Instead of diesel oil, they’ll run on Jet-A (jet fuel is basically kerosene) which is much cheaper than avgas. And about emmissions, I heard several years ago that 100LL (100 octane low led) avgas has more lead in it than regular automotive gasoline (“mogas”) that was leaded at the time.

No prob- I just thought you would’ve jumped on this. Thanks for your expertise. It reads as though you are leaning pro-diesel. Going diesel also gives me the opportunity to try biodiesel, further reducing the impact on the environment.

It could also be a result of stations switching to a winter blend of #1 and #2 diesel.

Possible, I suppose, but I’m not sure they bother with that here in Alabama. Incidentally, I fueled up tonight, and was surprised at how cheap the diesel was considering it’s only the middle of spring.

1.21 - Regular
1.41 - Premium
1.17 - Diesel

Two things:
There are some very clean-burning diesel engines being produced in Europe by Audi and Volkswagen. I believe it’s called the TDI system, but I’m no mechanic.

Secondly, I just wanted to point out that the city of Montreal is using buses to conduct a test on biodiesel. It will be using mixes of 5 and 20 % vegetable oil to standard diesel.