Diesel vs Gas environmental impact

[northboundtrain]

I don't want to start a debate about which is the overall cleaner fuel, because that is a huge question with many different factors involved. Suffice to say that diesel advocates often point to reduced CO2 when they suggest that diesel is ultimately the cleaner fuel. Much of their argument, I believe, is based on the inherently better fuel efficiency of the compression ignition engine.

My question concerns the btu content of the two fuels. Diesel has about 13-14% higher btu content per gallon, which is why comparing the efficiency of spark ignition vs compression ignition based on mpg is misleading. So is the claim that diesel is cleaner based on better fuel economy likewise exaggerated? If diesel has 13-14% more btus per gallon, does it emit that much more CO2 per gallon burned? If this is true, then a diesel vehicle would have to get 13-14% better fuel economy than a gasser in order just to have the same CO2 emissions. Or does diesel actually emit less CO2 per gallon (or even per btu)?

Also, how much energy and crude oil goes into producing the two fuels. Again, I know this is a complicated question because diesel is a by product of refining gasoline, so essentially you can't have one without the other I suppose, but which has the greater environmental impact in getting to the pump, if that can be measured?

[SVOboy]

Diesel does emit more CO2 per gallon burned, I forget how much, but it can be looked up easily.

I don't know about production though.

[omgwtfbyobbq]

I think the increase in Carbon is proportional to the difference in energy content, but offload efficiency is much better for diesel drivetrains, so there's also an improvement in thermodynamic efficiency during low power use. For instance, a 05 diesel and gasoline drivetrain in the same car result in 24mpg and 35mpg respectively, with a correction for energy content. Over the new EPA cycle, the diesel is nearly one and a half times more efficient than the gasser, in the same car. The more efficient the car is, the more pronounced this difference can be. At high load, the difference in efficiency is minimal, so if someone's commute consists of 90% highway at 70mph, there won't be a huge difference between diesel and gas. Otoh, if they can cruise to work in top gear on 40mph roads, there will be a much larger difference, maybe even a relative doubling in mileage.

[omgwtfbyobbq]

Ya really!

[SVOboy]

But there can be so many differences there besides fuel, like weight, gearing, power output, styling packages, blah blah blah!

[omgwtfbyobbq]

Inverse respectively.

[omgwtfbyobbq]

Originally Posted by SVOboy

But there can be so many differences there besides fuel, like weight, gearing, power output, styling packages, blah blah blah!

Not really. At least not for the comparison I used.

[SVOboy]

List the models, punk.

[omgwtfbyobbq]

Same trim level, 115hp gasoline engine compared to 100hp diesel engine. Diesel powered car weighs 2989, gasoline powered car weighs 2743. Manual transmission ratios are
Gasoline-3.300 1.944 1.308 1.029 0.837 (3.938)
Diesel- 3.778 2.118 1.360 0.971 0.756 (3.389)

[SVOboy]

Jetta?

[omgwtfbyobbq]

New Beetle. 05 was the last year there were similar sized engines. 1.9L versus 2L.

[SVOboy]

VW still sells a v5 in japan, weirdness...

[omgwtfbyobbq]

V5? Do you mean the 2.5L I5?

[SVOboy]

It said V5 on the back, that's all I know about it.

[omgwtfbyobbq]

Oh, looks like a badge name. Like a GTI or R32 or something...

[SVOboy]

Ah, makes more sense.

[vt420]

http://en.wikipedia.org/wiki/V5_engine http://en.wikipedia.org/wiki/List_of...170_hp_2.3_VR5

V5... more correctly VR5

http://en.wikipedia.org/wiki/Honda_RC211V also v5

Jeff

[omgwtfbyobbq]

Crazy! I never knew the VR6 wasn't strictly a V engine.

[2TonJellyBean]

And the VW W-12 engine that's derived from the VR6 sure isn't a 'W'!

[northboundtrain]

Here's the info: http://www.epa.gov/otaq/climate/420f05001.htm Diesel has 14% more carbon content, and so it emits 14% more carbon than gas per gallon. This means a gasser getting 40 mpg emits the same as a diesel getting almost 46 mpg. So I guess the claims by diesel advocates are generally inflated, though it must be admitted that a diesel will often exceed a 14% mpg gain over a comparable gasser. Sorry for asking a question I could have easily looked up, but I'm also interested in the overall impact of one fuel vs the other. If anyone has info on refining impacts, I'd appreciate it. Thanks

[trebuchet03]

Originally Posted by northboundtrain

If anyone has info on refining impacts, I'd appreciate it. Thanks

I can't back this up -- this is purely anecdotal....

A barrel of oil will have a certain affinity for X gallons of diesel and Y gallons of gasoline. Both of which are extracted using a similar process at the same time (it's something like a furnace weight separator - not sure on the official name).

From that knowledge alone, I'd say that refining impact is similar...

I had a chart that was related to this very thing... But I can't find it... I did, however, find this interesting chart (which you may be interested in)...


and this one... The reserve to production ratios

[omgwtfbyobbq]

Start here and investigate those terms associated with refining gasoline and USLD if possible. PM if ya bump up against any proprietary scienecy databases and want some more info.

[smay665949]

I am interested in power with economy. Here are some links to performance guru Gale Banks web-sight that may intrest you. He discusses diesel as a an economical and performance choice.

http://bankspower.com/Tech_dieselperf.cfm

http://bankspower.com/tech_futurefuel.cfm

http://bankspower.com/tech_synthetic.cfm

http://bankspower.com/tech.cfm