100 MPG Hummer?
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.
[Source: Autobloggreen]
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.
Sample engine efficiency map
[Source: Introduction to Modeling and Control of Internal Combustion Engine Systems]
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).
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.
Posted: April 28th, 2009 | Filed under: Design, Energy, Green FAIL, Transportation |
[...] More: 100 MPG Hummer? [...]
wonder how much the battery costs. it might cost as much as a small car.
Anyway, the CA governor may like it since he can fit into it. :p
Quote
And now for “the rest of the story…”
How do these guys at Raser come up with their 100 MPG? Simple, they claim that if you drive 60 miles per day that the first 40 is powered by electricity and the next 20 is provided by their 33 MPG onboard engine. Therefore, only 1/3 of the distance traveled was provided by gas at 33 MPG, so it’s as though you got the equivalent of 3 times 33 MPG, which equals 100 MPG.
Now let’s see what Raser isn’t telling you. First, their 200KW electric motor costs MONEY to operate! How much, you ask? Easy. If you drive 40 miles on electric power — half in the city and half on the freeway — you will spend about 1 hour driving (20 miles @ 30 MPH = 40 minutes, plus 20 miles @ 60 MPH = 20 minutes). Raser’s 200KW motor is rated at 100KW continuous, so 1 hour of driving will likely consume roughly 100KWH worth of electricity (100KW times 1 hour). The average cost of electricity in the U.S. is 11.5 cents/KWH; therefore 100KWH costs you $11.50, got it? That’s eleven dollars and fifty cents to go forty miles!!! Luckily, you get to go the next 20 miles on good old gasoline @ roughly 33 MPG, which would consume 6/10ths of a gallon of gas if the gas engine powered the vehicle directly. Unfortunately, it first has to power a generator, which then charges batteries, which then powers the electric motor. Still, lets be generous and assume that this gas engine takes you 20 miles on 2/3 of a gallon of gas, which costs $1.67 (2/3 times $2.50).
So the grand total to travel 60 miles in Raser’s shiny EREV (Extended Range Electric Vehicle) only cost you $13.17!!! Isn’t that great? Of course, you would’ve only spent $5.00 if you could’ve driven all of that distance powered by their good gas-mileage IC engine. Or you could’ve paid $7.50 in any vehicle that averaged 20 MPG. However, where’s the fun in that? Look, you’re driving a high tech “EREV”… ooooh! One that cost you an extra $25K, and that added an extra 1,000 pounds of weight to the vehicle. Nice extras, huh?? BTW, did I forget to mention that their 100KW motor only provides 134HP in continuous mode? But wait you say, it gives 268HP at peak operation. Yes, that’s about what the new Ford Taurus provides (except for the Ford Taurus SHO, which gives 350HP). So you’ll be riding around in your new EREV Hummer in a reduced 134-268HP powertrain… can you say “put, put, put”?
Does anyone see anything wrong with this?? Now do you see why Raser omitted mentioning the cost of electricity and only focused on their fuzzy-math MPG gas equivalent calculation? In reality, at today’s prices, their Hummer only got the equivalent of 11.4 MPG ($13.17 divided by $2.5/gallon = 5.27 gallons, and 60 miles/5.27 gallons = 11.4 MPG)!!!!!!!!
The fact is that electric vehicles have NOTHING to offer in solving America’s transportation needs. They are not cost-efficient nor are they technologically superior. The demand for electricity in the U.S. is expected to grow by a taxing 25% over the next decade. Raser’s Hummer draws 100KWH of electricity in order to travel it’s first 40 miles, which is well over 3 times the power that your house draws in a complete day! Talk about an instant energy crisis! It’s a good thing that battery technology is still limited and that they added an IC engine to extend the range, otherwise their Hummer would’ve used 150KWH of electricity, or more than 5 times the daily draw of an average home!!
This conveniently omitted information might explain why Raser has also entered the geothermal power market… they realize that switching to EV’s would require well over a 300% + increase to America’s annual electric power consumption.
My question is this, why couldn’t Raser be upfront and honest with us about the true costs of Electric Vehicles? Afterall, consumers have shown that they are willing to pay more for efficient green power.
Could their hesitancy in telling us the whole story be due to the fact that EV’s are neither cost-efficient nor green compared to standard IC engine technology?
Quote
@Dennis
Thanks for your detailed contribution. Yes, it’s essential to account for all the energy used to propel the Hummer, not just the gasoline. There are SAE standards that specify gasoline AND electricity consumption should be reported for PHEVs, and Raser completely neglected the energy drawn from the battery, intentionally misleading people.
I do have one comment. Assuming that the average power consumption during the electric only phase is 100 KW is a significant overestimate, even for an urban drive cycle with frequent stops and starts. To get a more precise estimate, you need to use Newton’s second law: F(t)=ma(t), where F(t) is the force required to push the Hummer (at time t), m is the mass of the Hummer, and a(t) is the acceleration of the Hummer at time t. Acceleration is how fast your velocity is changing. Once you know F at every point in time, then you can calculate how much electric power the electric motor needs from the battery to provide that much force. You also need to account for regenerative braking, i.e., when energy gets put back into the battery when the driver brakes. Once you know the net power consumption over time, then you can figure out how much total energy was required to drive the Hummer. I’m confident it will be less than 100KWh for 40 miles of driving, unless perhaps the driver is being unusually aggressive in how he/she is driving.
In general EVs are dramatically more efficient than gasoline or diesel-powered vehicles, so you normally do see significant overall energy savings when switching to electric drive (and the cost of electricity to drive a mile is normally much lower than the cost of gasoline to drive a mile, all other things being equal). EVs are an excellent way to reduce total energy consumed, and when battery prices go down and fuel prices go back up, they will be economically advantageous as well (this is another reason to encourage true-cost pricing of gasoline). While the electrical energy consumed is relatively small for the Raser Hummer compared to a Hummer powered on gasoline alone, that doesn’t mean it’s right to neglect the electrical energy consumed, and that’s the main reason the claims by Raser are so outrageous. This is definitely a Green FAIL.
Quote