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U-Haul is jumping on the low-carbon bandwagon by promoting their ‘clean gasoline’ moving trucks over ‘dirty diesel’, but this blatant corporate greenwash is endorsing choices that actually lead to increased carbon emissions. Have a look at a screenshot from this U-haul webpage:
U-haul is telling us here that using a gasoline-powered truck instead of a diesel truck would reduce CO2 emissions. This campaign is actually doing more harm than good. It may garner more business for U-Haul, but switching from a diesel truck to a gasoline U-Haul truck will actually increase carbon emissions. This advertising campaign will also lead to indirect carbon emission increases by perpetuating misconceptions about diesel. Let’s have a more careful look at the numbers used here.
The core of U-Haul’s claim of lower carbon emissions is that the amount of CO2 emitted by burning a gallon of diesel fuel (22.2 lb) is somewhat larger than the amount released by burning a gallon of gasoline (19.4 lb) [Data source: EPA]. So what is wrong with U-Haul’s claim? It is based on the (incorrect) assumption that diesel and gasoline trucks get the same fuel economy. What U-Haul doesn’t explain is that you can do a lot more work with a gallon of diesel than you can with a gallon of gasoline. Diesel fuel efficiency is typically 40% better than for gasoline engines. That’s a huge difference!
The better fuel economy is a result of two main factors: diesel has 11% higher volumetric energy density than gasoline, and the Diesel cycle allows for much higher compression ratios than the Otto cycle used in gasoline engines (which makes for a more efficient engine). In other words, diesel fuel has more energy packed into it per gallon (which is part of why it has higher carbon content), and diesel engines do a better job of converting that chemical energy into mechanical energy used to move the truck.
A valid comparison between gasoline and diesel trucks would be based on equal amounts of work, not equal mpg—this is what really matters to the customer. Consider a potential rental truck customer that has a set amount of stuff that needs to be moved from a specific start location to a specific end location. What we should be comparing is how much CO2 is emitted from a gasoline truck vs. a diesel truck for moving the same amount of stuff along the same route. If you account for the substantially better fuel economy, the diesel truck will emit far less CO2 than the gasoline truck. The U-Haul comparison assumes both diesel and gasoline trucks get 8 mpg. For this to happen, the customer would have to remove some of his load from the gasoline truck to improve its fuel economy so that it equals the fuel economy of the diesel truck (which is carrying the full load). In this case the gasoline truck is doing far less work, and is not moving all of the customer’s stuff. The U-Haul comparison strategy is unrealistic and deceptive. Readers who are unaware of diesel’s inherently better efficiency may be misled into believing that choosing U-Haul would actually reduce carbon emissions.
In the fine print above, U-Haul states that ‘actual gas mileage may vary’. The fact that actual gas mileage does vary, in favor of diesel by a large margin, destroys U-Haul’s claim that gasoline trucks are better with respect to carbon emissions. The ‘various reliable sources’ statement in the fine print should raise another red flag: U-Haul is not the least bit transparent about these distorted claims.
In the fine print you will also find links to articles about new regulations for diesel particulate, sulfur, and NOx emissions, which are unrelated to the comparison of CO2 emissions between diesel and gasoline. Ironically, these articles explain how diesel-powered vehicles will be improved significantly in the near future.
The statement in this advertisement that diesel trucks emit more carbon than gasoline trucks (per gallon) may be deceptive, but it is technically correct given all the stated (but unreasonable) assumptions. The running tally of ‘CO2 emissions kept out of the atmosphere by choosing U-Haul’, however, is flat-out wrong (flying in the face of the Truth in Advertising Act). Whoever did these calculations didn’t do their homework. Correct calculations would result in a negative value here; that is, switching to U-Haul would increase CO2 emissions.
Avoid “dirty” diesel
Mile for mile, diesel trucks release more toxic air contaminants, cancer-causing soot, and smog-forming emissions than gasoline-powered trucks. Greenhouse gas emissions from a gallon of diesel are 15 percent higher than those from a gallon of gasoline. That’s why all U-Haul rental trucks use cleaner-burning unleaded fuel.
The first two sentences, taken independently, are technically correct. Diesels do emit more particulates and other toxic gasses than gasoline engines on a mileage basis (at least with current emission control standards). And as I explained before, a gallon of gasoline does emit more CO2 than a gallon of diesel (14.4% more). However, putting these two statements together without clarification may lead people to believe that diesel trucks emit more CO2 on a mileage basis than gasoline, which is an incorrect conclusion. I roll my eyes at the third sentence. If U-Haul truly was concerned about carbon emissions, they would have transitioned their fleet to more efficient diesel trucks.
The financial savings claim in this ad is also incorrect. Not only do diesel trucks burn less fuel, but diesel is now less expensive than gasoline on average in the U.S. (gasoline: $2.691/gal, diesel: $2.616/gal, Source: EIA, June 25, 2009).
U-Haul is working hard to perpetuate incorrect negative stereotypes about diesel fuel and engines. An anti-diesel campaign magnifies their negative impact by delaying diesel adoption in the U.S. market. Switching to diesel-powered passenger cars could be a practical near-term solution to reducing carbon emissions and reducing dependence on foreign oil. We need to encourage the U.S. market to embrace diesel, not shun it. I want to note that diesel-powered transportation is not a long-term solution; we need to develop (as quickly as possible) a fossil-fuel free transportation system as a long-term solution.
What do you think of U-Haul’s CO2 marketing campaign? Why don’t you let them know (1-800-789-3638), and see what they have to say about it. Or, you could let others know (like these folks).
As an aside, if you want the ultimate in ‘green’ moving options, and you are moving locally and are feeling athletic, perhaps you would be interested in getting a few friends together for a ‘bike move‘.
Last week I posted a photo of a rather unusual license plate:
I had the thought a few days ago that this might be considered a Green FAIL (in the spirit of FAILblog). I’ve decided to add Green FAIL as a new category to Design Impact. Occasionally I come across things like this. Some are just funny, like this license plate, but others have more serious implications. I would love to see Green FAILs that you encounter. Please submit them to Design Impact, and I will publish as many as I can. What are some examples of Green FAILs?
A company trying to capitalize on public concern for sustainability by marketing ‘green’ products or services, which in reality either don’t help much, or actually harm the environment.
Over-the-top efficiency or other sustainability-related claims. Some may be legitimate, but I’ve come across claims that would violate the laws of physics, or are very misleading. (If something seems too good to be true …)
Humorously unsustainable activities or choices.
I’m sure you can think of many other things that would qualify as Green FAILs (and perhaps some green WINs). We can have fun, but please keep submissions family friendly and workplace appropriate.
Last week I wrote a post about cars powered by compressed air. I was fairly critical of the claims made by MDI, one company developing an air-powered car. Don’t get me wrong; it’s not the technology or innovative efforts that bother me. I think the idea of an air-powered car is pretty cool. Some of the claims made by MDI, on the other hand, do get me a little fired up. I watched the MDI video that I included in my last air car post again, and I am astounded at what it contains. First, MDI neglects (initially) the cost of compressing air and glosses over the energy loss of a compressed air system, but more importantly, they propose a ‘perpetual motion’ system for their car. I called this a red flag earlier. I want to explain why perpetual motion claims are a red flag. This drawing illustrates what they are talking about at about the 2:45 point in the video:
MDI suggests that they should use a compressed-air powered electric generator to power an electric air compressor to refill the air tank. They claim such a car will refuel itself and result in perpetual motion (perpetual motion violates the laws of physics). What do they think this system is going to accomplish? At every stage in the process energy is lost. Electric generators are not 100% efficient; energy is lost to heat and electromagnetic radiation. Air compressors put off a lot of heat, so again there is more energy loss. This system will recharge the air tank with far less compressed air than was used to compress it. The only purpose a system like this serves is to create waste heat! It will not extend the range of an air car, it will reduce it. It will increase overall energy consumption. Whoever proposed this does not understand basic thermodynamics. Does MDI not have any engineers on staff?
This reminds me of an April Fools post on Autobloggreen that describes a car that uses a miniature wind turbine to power the headlights. This is similarly impractical idea since the energy to turn the wind turbine comes indirectly from the engine that moves the car. Because wind turbines are not 100% efficient, this system would result in worse fuel economy, not better. At least the post about the wind turbine car was a satirical April Fools article, in contrast to MDI’s video.
I aim to keep most of my writing positive, but claims like this really need to be addressed and exposed for what they are. Either MDI really doesn’t know what it’s doing, or they intentionally are using a deceptive marketing approach.
I do want to point out that there are some cases where air-powered cars make a lot of sense. There is no local pollution with these powertrains, and the technology is very simple (and low cost). The video below describes another vehicle intended for use indoors, where zero pollution is important. Air cars on factory or warehouse floors may be an especially practical alternative since many of these buildings already have compressed air infrastructure.
The rotory air motor here is a more sophisticated design. It has smoother, more efficient operation than a reciprocating piston motor, like the one used by MDI. Keep in mind, however, that using compressed air to power a car involves a lot of energy loss. When the air is compressed to fill the tank, the air gets hot. This waste heat is lost energy, and is significant. Battery electric vehicles are a better alternative in terms of energy efficiency, but would likely cost more than air cars.
What do you think about air cars? Where else might they be practical transportation alternatives?
I think it’s fantastic to see exploration of new ideas like this. It has the obvious benefit of no local emissions, as well as freeing us to use renewable power sources to compress the air that powers the car. In addition, this technology is much less expensive than electric vehicles or hybrid electrics. However, when the air is compressed to put into the on board storage cylinders, the air gets hot (think about what happens when you use a bike pump). This heat is lost when the compressor and storage cylinders cool off, meaning that a lot of energy is lost in the process. This reduces the overall efficiency of the system. I have not done any calculations myself yet, and I don’t have any efficiency data, but I’m skeptical that an air car would compare in energy efficiency to an electric vehicle. There may be specific applications where an air-powered car makes great sense, particularly where purchase price is more important than overall efficiency and operating cost throughout the life of the vehicle. We need to strive for both freedom from fossil fuels and lower energy consumption. The air car addresses only the former objective.
Unfortunately the company overextends itself in the claims made in this ad. Early on they claim ZERO cost to fill up this car, conveniently neglecting the cost of compressing air. MDI acknowledges this cost only at the end of the ad. When they discuss an on-board compressor, they flaunt the term ‘perpetual motion‘, which is a huge red flag.
Innovation is essential to our progress, and I commend exploration of new ideas. But we need to complement exploration with healthy debate that keeps us honest and helps drive us to seek the very best solutions. I’m concerned that wild claims may hurt the transition to clean energy and transportation. Let’s put our ideas out there, but let’s be up front about what we have actually accomplished and what the real potential is. We can’t afford to be deceptive; even the appearance of snake oil marketing could damage the movement.
The Automotive Research Center, in conjunction with industry and government partners, has investigated a similar technology that does indicate some practical benefit: hydraulic hybrid powertrains. Unlike air, hydraulic fluid doesn’t change volume when compressed, so doesn’t heat up much when compressed. Hydraulic regenerative braking systems have been installed on heavy trucks (and even bikes). A hydraulic pump connected to drive wheels pumps fluid into a pressure accumulator while providing some braking force. When the driver is ready to move again the pressure accumulator feeds the hydraulic motor, which assists the conventional engine. This system has been shown to have significant energy benefit, at a low level of cost and complexity when compared to hybrid electric systems (although all energy still comes from fossil fuels). This may be a good short term patch for current vehicles, but we also need to be working on long-term solutions that don’t involve fossil fuels.
I would be especially interested in hearing from anyone who has experience with compressed air powertrains to learn more about both their benefits and problems. Has anyone found data on the overall efficiency (grid to wheels) of an air-fueled powertrain system so we can compare then quantitatively to EVs? Or, has anyone done any calculations to estimate the overall efficiency?
Raser Technologies unveiled last week at the SAE 2009 World Congress a ‘100 mpg’ H3 that has been converted over to a plug-in series hybrid. This powertrain configuration is similar to that of the Chevrolet Volt. You can read more about the plug-in Hummer here (complete with specs and videos). Sound too good to be true? Keep reading.
A series hybrid is in essence an electric vehicle with an on-board engine (typically gasoline or diesel) linked to a generator to recharge the batteries to extend vehicle range. The engine has no mechanical connection to the wheels. This powertrain configuration is more complex and expensive thanconventional powertrains, but has several advantages:
More Efficient Engine Operation: First, a little background on gasoline engine efficiency. The efficiency of an internal combustion engine (such as a gasoline engine) varies with how fast it is running and how much load is on it. Have a look at the figure below. It shows how engine efficiency varies with load and speed. The mean piston speed is proportional to engine speed (think RPMs), and the mean effective pressure is proportional to torque (that is, how hard the engine is twisting the wheels). The dark line at the top is the maximum torque curve for the engine; the engine is not capable of operating above this line. If you are cruising on the freeway, your engine might be spinning moderately fast, but only under moderate load if you are not accelerating, so your engine would be operating at a point in the middle of the graph, perhaps with an efficiency of . Suppose you are driving slowly in a parking lot; your engine would be operating at low speed and low load, and would correspond to a point in the lower left area of the graph below, perhaps with an efficiency around . Finally, if you are accelerating hard, your engine will be operating at or near the maximum torque curve at the top of the figure: near the top left as you are starting out from a stop, and then near the top right just before your transmission shifts to the next higher gear.
What do we mean here by engine efficiency? Energy efficiency is a ratio that describes how much energy you must put into something to get a desired result. In this case, we must put chemical energy into an engine (gasoline), and we are interested in the mechanical energy from the engine available to move the vehicle. So here, efficiency is the mechanical energy output of the engine, divided by the energy stored in gasoline used to run the engine. If the efficiency is 1.0, or in other words 100%, then 100% of the energy stored in the gasoline is converted to useful mechanical energy by the engine. This would be ideal, but is physically impossible. As with any heat engine, some waste heat must be rejected for it to work. The heat lost through your car’s radiator and exhaust system is waste heat, which comes from burning gasoline in your engine. Therefore not all of the chemical energy in gasoline is available to create useful mechanical energy, and combined with the effects of friction, flow restrictions, material temperature limits, and other factors, the efficiency of a typical automotive engine is far less than 100% (the efficiency shown in the figure above is actually very good).
It would be great if while driving the engine could spend most of its time in the parts of the engine efficiency map where efficiency is highest (high torque, moderate speed). However, a conventional powertrain has a direct mechanical connection between the engine and the wheels, meaning that the engine load and speed is constrained. The engine speed depends directly on the vehicle speed, what gear your transmission is in, and in the case of automatic transmissions, the load on the engine. If we assume the route you are driving and the speed at which you drive it is fixed, then the only way to get your engine to spend more time in efficient load/speed conditions is to change how the transmission shifts, and controlling this can only do so much (note that changing how you drive can do a lot to improve efficiency).
With a series hybrid, like the Raser H3 or the Chevrolet Volt, there is no mechanical connection between the engine and wheels. We are free to control the engine independently of vehicle load and speed. We can run the engine at the most efficient operating point the whole time if we would like. When the batteries are charged sufficiently, we can shut the engine off, but continue to drive the car. Note that everything to do with starting, operating, and turning off the engine is handled by an on-board computer; the driver doesn’t have to think about when to turn the engine on or off.
Here are some additional benefits to using a series hybrid powertrain:
Engine Downsizing: Because we are using the engine more efficiently, and because the batteries supply the power required for short bursts of high acceleration instead of the engine, we can get away with using a smaller engine. This means the vehicle can weigh a lot less, leading to even better energy efficiency (unless of course the batteries weigh more than weight savings from the smaller engine).
Regenerative Braking: The electric motors that drive the wheels of an electric or hybrid electric vehicle can be used as generators as well. This is important during braking, because energy that would normally be lost to heat (getting your brake pads really hot) is instead converted back to electrical energy and sent back to the battery. This improves the overall vehicle energy efficiency.
Electric-only Operation: Again, becuase there is no mechanical connection between the engine and wheels, it is possible to drive a series hybrid vehicle without the engine running. This means that you can drive for a while on batteries only. After the batteries are depleted to some predetermined level, the engine turns on to run the generator and charge the batteries back up. If your trips are mostly short, you could go for a long time without needing to fill up your gas tank. The engine is available for times when you need to drive a long distance.
The presentation of the Raser H3 at the SAE Congress is a great demonstration of better design and the effectiveness of a plug-in series hybrid powertrain, but Raser’s claim of 100 mpg is misleading. Take a careful look at how they are arriving at 100 mpg. A route of 65 miles is assumed, but the first 40 miles is electric-only operation. Sure, it averages 100 mpg over this 65 mile route, but what about the energy used during the battery-only phase? They are only counting the energy used during the last 25 miles of the trip! Raser has not accounted for the energy drawn from the batteries during the electric-only phase. To be fair, they should at least convert the electrical energy used to a gasoline energy equivalent, and include that when calculating their mpg claim. It will certainly best a stock H3, but will be a long way off from 100 mpg when all energy consumption is accounted for.
Approaches for measuring energy efficiency for plug-in hybrids have been debated the last several years. SAE is developing standards for this. SAE standard J1711 stipulates that gasoline and electricity usage per mile are stated together. Raser skipped out on the second part of this standard. This is clever marketing, and is helpful in generating enthusiasm for the capabilities of advanced powertrains, but is deceptive nonetheless.
The evening of Earth Day I listened to a piece on NPR by David Gorn (Ban The Burger, Save The World). He describes how numerous cafés and cafeterias are participating in earth day by reducing or eliminating beef and cheese from their menus. It turns out that these foods have a large carbon footprint, and have adverse health effects beyond the direct consequences of consumption (energy and carbon intensive foods contribute to pollution and climate change).
Gorn interviewed diners who sounded pleased to be doing their part for the environment by skipping beef and cheese. This effort certainly brings more awareness of the current state of our agricultural system, and perhaps paves the way for substantive changes. The last line, however, was a bit disappointing. Gorn developed reasonable rationale for cutting back on meat, cheese, and other carbon and energy intensive foods, and then concluded that this rationale “makes giving up a cheeseburger one day a year, seem a little easier to swallow.” It almost sounds like skipping a cheeseburger once a year is sufficient to make a big impact. I’m on board with events like this to get us thinking, but they need to be followed up with clear acknowledgment of steps that would bring real change. Otherwise, efforts like this leave participants feeling green, but accomplish little else.
Last month Joseph Romm scrutinized a New York Times article ‘Five Beginners’ Steps to a Greener Home‘ here. As with the once-per-year cheeseburger ban, Romm reveals that the ‘beginner steps’ may have far less impact than expected, and explains that advice like this can actually be counterproductive. Following these easy steps helps someone feel green, but may placate aspirations to make meaningful change. Romm outlines his core climate solutions here. Notice that energy efficiency is at the top of the list (which can be strengthened through better engineering design). Romm also states that his top suggestion for individuals is to “get political, since the changes required can only be driven by national action.”
Going back our food system, we need to take a broader view when planning reform. We need to design better agricultural system, supported by sensible agricultural policy. We need to develop more detailed awareness of this topic across our society to foster support for meaningful change. Michael Pollan has proposed some compelling changes in his book The Omnivore’s Dilemma, and in his open letter to President Obama, Farmer in Chief.
The media attention paid to green initiatives right now is truly fantastic. However, it requires a discerning citizen to separate the superficial from the substantive. What do you think about the way sustainability issues have been addressed in the media recently? Is it helping move public dialogue and opinion in the right direction? What ideas to you have for accelerating our shift to a sustainable path?