BMW 5 Series Beat Prius in MPGs?

Can you run your Prius without a supply of gasoline? Didn't think so.

 

Looks like we have more anti-Prius trolling. Maybe all the Prius drivers should start hanging out on the Jetta and BMW message boards?

The above is an amusing apples to oranges. To put more lipstick on that pig you have to lump the Prius in with lawnmowers, boats, and everything else operated by gasoline.

Considering how many poorly running gasoline vehicles there are out there, I'm not surprised by the discrepancy. Additionally, small gasoline engines (trimmers, mowers, boats, etc. emit quite a bit of the total as I recall) Diesel is used more for commercial transport where having a decently tuned vehicle is more critical to the bottom line. So I'm not surprised although I am amused.

Talk about a massive departure from reality. :cheer2: What a load of bullocks. You'll have more liquid losses than that from the fills alone in no time. You think droplets and such won't be "evaporative emissions?" Is there a tiny vacuum truck cleaning them all up?

 

I do hang out on Jetta boards.

Oh and the "troll" you are arguing emissions with is a climate scientist that studies emissions. Though you might want to know.

 

Well that troll might want to reconsider how the box is being drawn then because there are some serious problems with the analysis presented. It won't pass a simple reasonability test. Back to the drawing board.

 

Where? These are EPA data, not mine.

And where am I bashing the Prius? I'm just defending diesel vehicles by pointing out that there are more emissions from the operations of a vehicle with which to be concerned than just what comes out of the tailpipe.

 

You've mixed so many bases in your expansion that the result is meaningless. You've mixed a narrow EPA determination of an aspect of fuel supply (only evaporative) as representative of the broader picture...for an individual car. Nevermind that the ratios are at odds with those ambient values you gave earlier. (This becomes even more noticeable when you factor in that the ratio of gasoline to diesel use in the U.S. is something like 2:1. There is at least a decimal order of magnitude problem in the ratios.) You tried to broaden this so much that the result was a fundamentally flawed basis, a trap of your own making.

Although my refinery process knowledge is limited, costwise conversion to diesel in the U.S. appears capital intensive and more expensive to the consumer than improving gasoline efficiency. Our refineries are not set up for the reverse ratio and gasoline prices are likely to be depressed next to diesel if consumers continue transitioning away from the real culprits: heavy higher performance SUV's, trucks, and cars (in roughly that order.) So if we end up with excess gasoline capacity anyway, then add demand for diesel, you can see a long sustained price discrepancy that will make diesel conversion at the consumer level very unattractive...perhaps worse than it is today. Refiners won't make such a shift without demonstrated sustained diesel demand increase.

 

The source apportionment studies included both evaporative and exhaust HC emissions and are from monitors in urban locations. The 80% ambient HC data are from 2 studies in the Southern California Air Basin in the Los Angeles area (Fujita, et al, "Weekend/Weekday Ozone Study in the South Coast Air Basin.").

The second more recent study (Steven G. Brown, Anna Frankel and Hilary R. Hafner; “Source apportionment of VOCs in the Los Angeles area using positive matrix factorizationâ€. Atmospheric Environment, Volume 41, Issue 2, January 2007, Pages 227-237) assigns between 71% and 80% of all ambient HC emissions to gasoline with 47% - 57% assigned to evaporative gasoline emissions.

Another study (John G. Watson, Judith C. Chow and Eric M. Fujita; “Review of volatile organic compound source apportionment by chemical mass balance.†Atmospheric Environment, Volume 35, Issue 9, March 2001, Pages 1567-1584) concluded that 50% or more of ambient VOCs was assigned to gasoline exhaust and gasoline vapor in “many†of the studies reviewed. This included studies conducted in other urban areas.

A European study (Heidi Hellén, Hannele Hakola and Tuomas Laurila, “Determination of source contributions of NMHCs in Helsinki (60°N, 25°E) using chemical mass balance and the Unmix multivariate receptor models.†Atmospheric Environment, Volume 37, Issue 11, April 2003, Pages 1413-1424) assigned roughly the same percentage to gasoline exhaust and gasoline vapor as a local contributor (52% gasoline exhaust and 33% from gasoline vapor). Diesel exhaust was assigned 0.2% of the ambient HCs (no mention of diesel VOCs).

The EPA data come from AP-42 Chapter 5 (http://www.epa.gov/ttn/chief/ap42/ch05/final/c05s02.pdf) as follows…


Loading losses from loading a tanker truck at pipeline terminal = 0.6 pounds per 1000 gallons for gasoline (from “sample calculation†on page 5.2-7); 0.0022 pounds per 1000 gallons for diesel based on the same calculation using vapor pressure of diesel fuel under same ambient conditions (from Chapter 7 of AP-42)

Transit losses = 5.0 pounds per 1000 gallons for gasoline; 0.014 pounds per 1000 gallons for diesel (from Table 5.2-5 on page 5.2-12)

Losses at gas station = 2.0 pounds per 1000 gallons from Table 5.2-7 on page 5.2-15. I did not include the evaporative emissions from "Stage 2" refilling because it's my understanding that ORVR replaces that control technology.

The loss from gas stations for diesel fuel is from http://www.epa.state.oh.us/dapc/engineer/stage2/10b.pdf page 4 section 2.ii.(a) – 0.027 pounds per 1000 gallons.

Total = 7.6 pounds per 1000 gallons for gasoline; 0.0432 pounds per 1000 gallons for diesel fuel (if my math is correct).


This all assumes the best available control technology for controlling fugitive VOCs.

If you have a better methodology of determining evaporative emissions of the respective fuels, let me know.

At any rate, the evaporative HC emissions are just as harmful as “tailpipe†HC emissions from an air quality perspective.


I'm not arguing the other pro and cons of diesel vehicles (e.g., the current price spread between diesel and gasoline), just the "diesels are dirty pigs" assertion.

 

That sounds like a very non-representative sample to start with. Think about it: What percent of diesel consumption and refueling is in urban areas? It's going to skew figures dramatically toward gasoline. Perhaps I am mistaken, but much of the diesel use appears to be along highways for trucking, diesel locomotives, and greater use in rural areas for pickups and farm equipment and material industries. Yes there are buses and other frequent uses of diesel in urban environments but they appear paltry compared to gasoline use. Then add to the problem in that much of gasoline use in cities is inefficient short distance (bigger issue for non Prius.) Then add in the small gasoline engines (mowers, leaf blowers, trimmers, construction, etc) used with no pollution controls and far greater liquid/vapor losses in filling and you have a really lousy sample for the comparison you were making. Anticipated impact gas vs. diesel is an order of magnitude bias that will overcount gasoline and undercount diesel nationally.

But I understand the focus on urban areas. The concern for smog is metropolitan areas. Fair enough, but that doesn't support the wider argument that you made. And for the record, I'm far less concerned about short term VOC's than persistent problems such as CO2.

However, if you were to do urban sampling of 50% diesel/50% gasoline passenger vehicles (no other engines) I'm confident that you would achieve a far different result. And what we are discussing is a comparison of passenger vehicle choices in equivalent services, not uncontrolled small equipment engines or long haul vehicles. And with diesel cars being a tiny percentage of the passenger car market urban sampling won't tell you much of anything at present.

Another problem with the sampling is that I doubt a gas only sample makes sense for a loss estimate. I've done a lot of sampling work in petrochems and would expect a badly skewed result when sampling a lower volatility material only from the gas phase in a non-closed system. The balance isn't closed. Two phase sample gathering in such an open system is problematic to put it mildly. I've knocked my head against a few walls trying to resolve two and three phase stream sampling problems before.

They've done no accounting for liquid residuals. For gasoline with a higher vapor pressure it's not likely to make an order of magnitude change although it will increase. For diesel, expect about two orders of magnitude increase based on the number above. The devil is in the details of the connections and loading procedures though. Perhaps they have some reason to anticipate no liquid residuals on couplings or hoses...but I've not seen that with low volatility materials. I've seen the illusion of it with high volatility materials...since they dry quickly.

There is some sort of problem with the table in the loading section for "vapor balancing" as the vapor balance should go to a vent condenser minimizing losses (pretty standard in the plant material handling operations I've worked with, but we had more volatile, reactive, and flammable materials than gasoline.) With vapor balancing emissions should be much lower, instead they have them higher. You seem to have accounted for their error in this section somehow, their table does not. Not sure what they did in mixing bases across references.

Is the 5.0 a carryover from an earlier part of their loading table above because the transit section on the following page lists 0-0.01 lb/1000 gal typical for "load with product" transit losses, and 0-0.11 for "return with vapor." So taking the higher end of "typical" and summing I get 0.12 lb/1000 gallons.

Closer but the 1.1 lbs of displacement losses should be omitted for the Prius since it has that bladder system. So I get 0.3 from balanced submerged fill and the 0.7 spillage.

Note the 0.7 spillage also applies to diesel below.

Add the 0.7 spillage for equivalent liquid basis.

With adjustments above to your figures I get:
Gasoline = ~1.7 pounds/1000 gallons
Diesel = ~0.74 pounds/1000 gallons

Sounds reasonable for the balancing and vapor recovery systems.

I was referring to the economics of diesel compared to the Prius. I didn't call it a "dirty" pig as the hydrocarbon emissions side of it is tertiary for me (with economics and CO2 being primary.)

 

Anyone know if there are plans to bring a diesel hybrid to market? Seems like it would be great in terms of efficiency.

 

Don't know, but I don't think it's as skewed as you think. Most gas stations (including truck stops) are clustered around urban locations, and refueling diesel locomotives also generally occurs in urban area (typically city core locations). Diesel generators, construction equipment, etc., also are also used frequently in urban locations.

I don't disagree that a significant portion of the gasoline-based ambient HCs in urban locations are from small gas engines and gas storage cans. But there's still an overwhelming portion of gasoline that's used for automotive purposes, something like 93%, IIRC.

So have I in previous jobs I've held. I've also calculated headspace vapor concentrations and estimated fugitive emissions for TRI reporting. If you've also done this, then you probably know you have no choice but to following EPA's methodology for determining the emissions.

I also am (was) not completely satisfied with the EPA methodology on numerous emissions calculations, but that's all we have as far as I know.

Again, I don't blame you for doubting EPA's data/methodology, but we still need empirical data to use in lieu of the EPA data.

It's my understanding that the emissions from the tanker loadings are from headspace displacement while the losses in "transit" are breathing losses from the headspace. This seems reasonable to me since a tanker truck would likely encounter changes in temps as well a (potentially) changes in atmospheric pressure, depending on the length of the transport, especially unloaded since essentially the entire tanker compartment would be headspace.

I already accounted for the 1.1 pounds of displacement losses. So the gas station losses (per EPA) would be 0.3 pounds per 1000 gallons (tanker off-loading) + 1.0 pounds per 1000 gallons (storage tank headspace breathing) + 0.7 pounds per 1000 gallons (spillage).

Fair enough...

I get:
Gasoline: ~7.6 pounds/1000 gal
Diesel: ~0.74 pounds/1000 gal

OK - I apologize if I mistook your "putting lipstick on a pig" comment for implying diesels are inherently "dirty pigs" (I've seen that enough in other message boards/blogs to jump to that conclusion.)

I applaud you and everyone else here that own a Prius or any other max. fuel efficient vehicle. I have a son who's serving in Iraq (and probably soon Afghanistan) as a USAF helicopter pilot (CSAR). My main concerned is that the $$ we spend on fuel is at least indirectly going to fund weapons capable of shooting his helicopter down (and yes, he's reported that their helicopter has been fired on numerous times.) I've been paying ~$0.20 MORE for biodiesel than conventional petro-diesel (which itself is unrealistically higher than gasoline now) because of my conviction on this.

I'm a diesel proponent because it appears to me that no matter what application you consider - conventional, hybrid, whatever - you get 25% - 55% greater efficiency.

Toyota WAS apparently considering a diesel Prius (Update: Toyota Exec Says Diesel Prius Hybrids Possible), which I would fully support.

By the way, whatever happened to the 80 mpg (gasoline equivalent) diesel hybrids developed under the PNGV program? We taxpayers wound up paying untold millions for an interesting engineering experiment?

 

Thank you for the update. Increased efficiency and torque would be great.

 

It appears Peugeot will be marketing diesel hybrids in 2011...

Diesel hybrid technology will be in Peugeot and Citroën showrooms in 2011 - AutoblogGreen

Most likely only for the European market however.

Here's an article on the GM entry (Precept) for the PNGV program...

GM's Precept Hybrid Gets 80 MPG - Popular Mechanics

 

I strongly disagree with that. Most of the truck stops are exurban from what I've seen. Truck transport spends little time in the same stretches of road as the bulk of the urban passenger traffic by comparison. Most of the miles on these vehicles appear to be outside of the urban zones that would be sampled. I would be surprised if the relative depletion is only 2:1. Let's just say that most of the gas stations along the highways inside the urban areas I've lived do not have appreciable 18 wheeler traffic. I see those well represented in the corridors between zones.

And most of the diesel "passenger" vehicle sales in the U.S. are actually light trucks. These are going to be in greatest concentration in rural areas and suburban areas from what I see every day.

Diesel trucks (esp. commercial) have larger tank volumes on average, thereby reducing fill losses per volume as well.

But that remaining 7% is where a large percentage of the gasoline evaporative emissions are emanating from. I know that my lawn equipment and tanks lose a lot through breathing (and leaks) compared to what they burn. And the engines themselves leave a lot of unburned gasoline. Add to that filling a 1 gallon jug can result in about as much spillage as filling a car or truck. Then you have to fill the equipment adding an additional transfer and spillage, and mixes with oil for some of the equipment. The loss ratio is tremendous compared to a car because you have roughly twenty times as many transfers per unit volume with no controls, and very low consumption rate per tank volume.

Let's take an example of what all this could mean in the real world. Say you have an urban sample point showing 50% hydrocarbons from gasoline and 1% from diesel. Ignoring the inherent problem in vapor samples of the gas vs. diesel and taking them to be correct one must account for:
1. The difference in national gasoline vs. diesel use (roughly 2:1). So if you normalized for a 1:1 usage ratio you get ~50%/2% emissions.
2. The difference in urban vs. non-urban gas/diesel ratio. For this I'm going to assume another doubling. I won't begin backing out gasoline percentage yet, but this moves the normalized diesel contribution to 4%. It is still over an order of magnitude less and sounds good.
3. Now factor in small engines to unburned hydrocarbon gasoline. It is probably on the order of half of the gasoline emissions. At this point we have 25% gasoline (auto) vs. 4% diesel (heavy equip plus auto). Now we are getting closer to a real comparison and diesel has an order of magnitude advantage...or so it appears.
4. Now factor out 18 wheelers and other non-passenger vehicle diesel. This is hard to do as the U.S. passenger car/truck diesel fleet appears to be so small that there is not much left...however, I suspect the calcs below to be more representative of the actual difference.

Not the 5.0. The other yes, but the 5.0 does not apply for balanced controlled systems. If I understand correctly that is what is used in the smog areas. With vapor balancing you do not vent the head space on the tank or tanker (and the document refers to the hatch seal.) There will be a vent somewhere to handle the smaller real life displacements of the terminal tanks but also a vent recovery system of some type that will achieve some form of recovery. Note that the table header says "uncontrolled" which is the opposite of the condition being analyzed.

So no, I can't support that figure for truck loading in the vapor balance system because it is not "uncontrolled" and is not resulting in actual displacement to the vent IF it is vapor balanced or if there is a vapor recovery unit. Now perhaps this is just my misunderstanding of what they are actually doing vs. the terminology used or the case you are giving. However, I'm looking at this as I've seen it depicted and described before and considering the movement of the vent gas between vessels.

And of course it will be different (higher) for non-balanced loading systems outside the smog zones.

OK, I see what you are pointing at now--breathing losses in the station tank.

Adjusting I get:
Gasoline: ~2.7 pounds/1000 gal
Diesel: ~0.74 pounds/1000 gal

 

While the BMW 520d (which will likely never make to the USA) may have great fuel economy, you still have to deal with two issues:

1) Diesel #2 fuel in ULSD form is often 40 to 70 cents more per US gallon than 87 pump octane unleaded fuel. That right there may erase all the fuel economy advantages of a diesel engine.

2) Cleaning up diesel exhaust to meet the EPA Tier 2 Bin 5 standard is a VERY expensive proposition. For example, the BMW 335d and the Mercedes-Benz BlueTec models require the use of a very complicated exhaust emission control system that not only has a big particulate trap, but also a urea gas injection system to reduce NOx emissions. Small wonder why here in the USA there is more interest in hybrids like the Prius.

 

I guess we fundamentally disagree on this point because that doesn't correlate to my experience.

Based on my observations, most large urban areas have multiple interstates and interstate segments, all of which have interchanges every mile or two, and most of which have multiple fueling locations, most of which carry diesel fuel.

On the contrary, in rural areas, interchanges are typically every 10+ miles and even then there are typically fewer gas stations and even fewer that carry diesel.

Plus, virtually all truck stops also have gasoline pumps. So I don't see any clear trend in relative fuel usage between gas/diesel in urban/rural areas. I'm keenly aware of this since, as an owner of a diesel vehicle, traveling in very rural areas is about the only time you have to worry about finding a diesel pump.

True, but most mowing occurs outside urban locations. Other than city parks, there's not much grass to mow in urban locations, typically anyway.

You're correct and I concede this point. I admit I missed the "uncontrolled" qualifier in the heading.

So your emission factors look reasonable based on the correction.

 

Carry it, yes. Have 18 wheelers filling there? Not much in the urban areas. In a ring around them, yes but outside the urban areas primarily and at the various highway interchanges. That's based on the various regions I've lived over the past two decades (Texas, Southeast, Midwest).

Must be major differences in where you live because diesel has been a mainstay in the rural areas I've been to in various regions of the U.S. There are a lot of diesel trucks, tractors, and other farm equipment. Plus the big truck stops tend to be outside the urban areas.

The primary filling of 18 wheelers I see is at truck stops big and small on the arteries outside of the urban and residential areas. Yes they have gasoline pumps, but the gasoline traffic does not appear to be primary (especially considering the quantity per fill.) While I see many big trucks in the traffic stream between cities, I don't see them filling in town. I do see them filling outside of town.

Perhaps this is true for Southern California and in the densest centers, but in the residential areas still in the urban/suburban zones within the belts I've lived there was plenty of mowing. Not much mowing out in the sticks by comparison (and some of that is mowing hay with a farm tractor.)

As example of the potential differences when I lived in Mountain View, CA some as a boy I don't recall much mowing although there were lawns. It only rained a couple of times in the year and a half I lived there. That is completely different from what I've observed in other states.

California does have some different rules so perhaps this has impacted where diesel is used there. That and climate differences might explain our observations.

I found some 2000 data for diesel and gas consumption in CA and the ratio was way different than the nation as a whole. 5.25 gals gas/gallon diesel. Found a 2004 chart that shows the same effect, with California having some of the lowest per capita diesel consumption among the states.

EDIT: Not sure why, but I misread your location as CA when it is TN...oh well.