Thursday, October 1, 2009
This discussion will be followed up by a related discussion on the stationary grid storage devices later this year.
We will have a busy weekend attending Lexington Energy Fair on Sunday and Altwheels 2009 on Monday. 56 vehicles of different sizes and applications, including MIT Porsche 914-EV,are expected at Altwheels.
Tuesday, September 15, 2009
In early fall, we always try to engage MIT community in our outreach efforts. We had a superb turnout of incoming undergraduate and graduate students. If you are interested in joining the team, please see this page.
If you are looking to make immediate impact, check out the MIT Facilities Transportation page. It lists multiple options available to MIT students and employees. Students can take advantage of Zipcar heavily discounted membership and of subsidized T passes. Employees also qualify for Alternative Transit Subsidy and Bicycle Commuter Benefit Program.
Wednesday, August 26, 2009
Emissions from tailpipe.
Gasoline and hybrid-electric cars emit through their tailpipes. They produce emissions and reduce air quality in the urban centers where population density is high. An electric car does not have a tailpipe. Here is a chart of CO2 directly emitted by the cars during the One Gallon Challenge. [Based on DOE data, more info at Carbon Dioxide FAQ]
Emissions from well to wheels.
Even though an electric car does not have a tailpipe, an electric car produces greenhouse gas emissions where electricity is generated. These emissions are usually counted as "well to wheel" emissions, that is, a full life cycle of fossil fuels from their extraction to actual process of burning. They are differentiated from "tank to wheel" (or "plug to wheel" for electricity) emissions from the tailpipe.
Gasoline-powered cars, both conventional and hybrids, also produce upstream emissions. Most significant ones are emissions from the oil refineries that convert barrels of oil in gallons of gasoline. [Based on Argonne National Lab GREET]
A few comments:
- Since we kept track of when we charged the car, we know that natural gas was used as a fuel to produce electricity for our drive. In general, you do not know which fuel was used to produce electricity for your air conditioner or flat screen TV. A common approach is to take US average grid fuel mix with 50% coal, which is almost twice as polluting as New England grid.
- The 75 MPGe well-to-wheel number quoted in the AutoBlog was based on the US average grid. Had we taken New England numbers, we'd get above 100 MPGe. Had we charged our car with wind or solar power -- no fossil fuels used -- we would have infinite MPGe!!!
A conventional engine CNG vehicle, for example, the only mass-produced available in the states Honda Civic GX would not be able to rival an electric car because it lacks a hybrid option. There have been prototypes of CNG Hybrids, for example, Toyota Camry CNG Hybrid and Opel/(Saturn) Astra Caravan CNG Hybrid, demonstrated in the past year.
CNG Hybrids or Electric Cars?
As a society, should we focus on electric cars or CNG Hybrids?
Advantages of CNG Hybrids.
- Price. Electric cars are quite expensive due to the cost of batteries. When our Porsche was built a few years ago, the battery cost for ~100 miles range was $36,000. If the car were mass produced today by a major automotive manufacturer, the battery cost would be closer to $15,000. It is still much more expensive than a hybrid powertrain.
- Leakage. Natural gas leaked from the refueling stations and from the car itself due to leaky hoses is a potent greenhouse gas, four times as damaging as CO2. Because of that, developing a complex infrastructure for natural gas refueling may end up producing just as much harm to the climate as today's gasoline cars.
- Renewable energy. Electric grid in the US will become greener with time. Emissions from the grid are already tightly controlled and budgeted (see RGGI, an initiative by ten Northeast and mid-Atlantic states). Addition of renewable sources, such as wind energy or solar power, to the fossil fuel powered grid will inevitably reduce well-to-wheel emissions from electric cars.
An average car in the US lives for about 15-17 years. An electric car sold TODAY emits as much greenhouse gases as TODAY's CNG Hybrid car. In ten years, an aging CNG Hybrid car will emit the same amount of CO2 per mile or even more, due to leaky hoses. In ten years, the same electric car will emit less CO2 per mile because its electricity will be cleaner. Electric cars are future-proof. That is one of the reasons our team is the Electric Vehicle team.
Tuesday, August 25, 2009
We monitored the charging behavior of the car closely and matched this information with the hourly data from ISO New England (wikipedia: about).
Here is a plot of electricity demand in New England with the profile of car charging overlayed. Both axes are in the units of power, MW stands for a megawatt (1 million Watts), and kW is 1000 Watts. An average incandescent light bulb is 60 Watts, an average compact fluorescent bulb is 20 Watts, and an average car has about 160 horsepower, equal to 120 kW. That makes 6,000 CFL bulbs in an average car.
The electricity demand follows a fairly typical summer profile. We use much more electricity in the afternoon (peak demand) than at night. The main use during the day is air conditioning.
The car charges whenever it is plugged in. Most electric cars will be charged at night in garages, on driveways, or on public charging spots. Just like we charged at our friendly hosts, Ford of Greenfield. We also charged during the day, in fact, during peak demand. Did it matter for the utility company? We'll see shortly.
United States electricity grid consumes about 50% of coal. Electricity produced with coal is particularly "dirty". Yet all states are quite different. Here is a fuel mix used in the New England: coal is only 11%, and renewables (including hydro) is greater than that. As you can see, the electricity demand on August 19th and August 20th were less than maximum capacity, so we did not run the dirty diesel generators.
The car charges "on top" of the demand bar, so we used capacity from a combined cycle natural gas plant. For this race, our Porsche was actually powered by the natural gas. It is a fossil fuel, yet its source is all domestic.
We were concerned whether our electric car mattered for the utility since it was being charged at peak. For the comparison, we looked at the difference between two consecutive days, Wednesday and Thursday. Wednesday was slightly hotter, so consumers used a bit more electricity. A difference between Wednesday peak and Thursday peak is 871 MW sufficient to recharge 414,762 electric cars like our Porsche
We will continue with the summary of CO2 emissions from the race.
View Larger Map
Both in Greenfield and in Boston, we had a tent for the car and a lot of visitors. Outreach and public education is an important part of our effort. For everyone who stopped by to see our car last week, thank you.
A day before the race, we drove from Cambridge, MA to Greenfield, MA. We completed this drive on a single charge during the prior night. In Greenfield, MA we charged using 240V AC at Ford of Greenfield which generously let us park there at night.
However, we were not able to fully charge during night due to logistical difficulties, so we started the race with 80% full batteries. We had to recharge on the way. Luckily, Colonial Dodge of Hudson, MA let us park next to their service bays during the day and fill up our battery.
We also had two cars, a hybrid-electric Toyota Prius and conventional Pontiac Grand Prix which drove with the Porsche. We took the chance to compare the vehicles against each other considering all three cars drove together along the same route.
Toyota Prius ran the race at very respectable 52.9 mpg, while the Pontiac Grand Prix did 22.8 mpg, fairly typical for a midsize sedan. We observed that fuel economy measured in mpg is not as telling as fuel consumption, usually measured in gallons per 100 miles or in liters per 100 kilometers, a European metric. You can readily see a difference between equivalent fuel consumption of an electric, a hybrid and a conventional car on this plot.
More updates are coming about our recharging experience and about our greenhouse gas footprint.
Update: There was quite a bit of press coverage for this event.
One Gallon Challenge: alt-fuel "race" cars get up to 164 MPGe
Friday, August 21, 2009
There are three main things to consider: (1) Cell chemistry (2) Power source (3) Chargers and (4) Battery pack design.
The good news is that it's all totally feasible - though research & development is obviously required! A123 has already developed the cells necessary.
Remember that drivers would not rapid recharge all of the time. Most of the time they would charge EVs for the lowest cost - slowly - over night in their garage. But in the event they need the extra range, rapid charging should be an option.
Included is a chart Shane and I (with help from professional electrical engineer Dave Rodgers) put together. It shows how you could rapid recharge a motorcycle at home, while a sedan would require higher power - which is already available in most industrial buildings (think Home Depot, Best Buy, etc.).
Thus our vision is that the rapid recharge stations would not be at home - but rather at fueling stations like Hope Depot, Shell Gas Stations, etc. This is totally feasible - and the power already exists in many of these buildings.
(click to enlarge)
Here she is parked outside the Caltech student machine shop - it's place of birth:
Now I'm back at MIT - and found some like minded enginerds that are interested in some e-motorcycle research.
Paul, Mike, Shane and I have been working on a rapid recharge pack for the above motorcycle (aka eMoto). We're designing/building a charger that will charge the pack in 10 minutes. The same design can be scaled up for any pack size - including a car.
Here are some pics of our very recent work:
Battery welding (thanks to our sponsor Miyachi):
We're very constrained with space, etc. Here's a finished module (BMS boards sitting nearby - provided kindly by Texas Instruments - thank you!!):
One of the lithium modules on the motorcycle - datalogger on tank:
One module (as shown) - lead vs. lithium - you should feel the difference!
Lead acid: 333 Watt-hrs / 44 lbs of battery (actual)
A123 Lithium: 380 Watt-hrs / 10 lbs of battery (predicted - includes weight of enclosure, etc.)
Working on the charger (gray box w/ lid removed):
We're also using a commercial charger (which can't charge quite as quickly - roughly 20 mins) - with help from Manzanita Micro - (thanks Rich!).
Thursday, August 20, 2009
Sprockets and chain guard are in place, with Mike grinding a small channel to make room for the motor encoder wire.
Kevin, finishing the enclosure for the trunk-mounted battery pack.
The orange high-voltage (356 Volts) shielded battery cable runs from the rear to the front of the car, from the battery pack to the motor controller.
Arya has been working on getting the hood latch assembly back in place - it had to get cut off to make room for the motor controller enclosure (the clear plastic box to the right of the engine bay with the orange cables running into it).
Saturday, August 15, 2009
The Porsche crew has been hard at work over the last month preparing to climb Mt. Washington and compete in the 1 Gallon Challenge.
Tyler, Mike, and I decided that Thursday was not the best day to do the hill climb, many of the concerns regarding braking and regen performance had not been adequately answered, and with only 3 people going, it didn't make sense to spend so much time driving there and back.
Heating only becomes an issue when driving in 3rd (i.e. high torque, low revs). We have motor temperature logs & need to analyze exactly the parameters when the motor overheats. It drives very well in 2nd, which is perfect for the country roads that are along the route. At the end of the drive, some capacity mismatch seemed to exist between the cell groups in the pack, but they all charged up perfectly balanced (so there isn't too much cell efficiency mismatch). Since this is the first time the pack has actually been balanced and fully cycled, we're hoping that some of the mismatch will work itself out as we cycle the pack more.
Saturday, August 8, 2009
We built the center console completely out of wood and woodworking bits, except for a few custom sheetmetal brackets. These are the same materials which the stock Porsche center console, on which our design was based, was made from. The center console is a highly visible and functional fixture in the car, so there was a laundry list of requirements in designing and building it. It had to look stock, not interfere with the operation of the accelerator, shifter, or adjustable seats, fit the National Instruments touch screen and cRIO controller, be sturdy enough for abuse, provide room inside for wiring and outside for the eventual addition of switches and indicators, and provide easy tool-less access to all the wiring and electronics inside it.
We mocked up the entire console in cardboard before making a run to Home Depot for lumber. The cRIO was mounted against the front wall, above the passenger's toes, we added a floor board under the passenger's feet to protect the wiring (it was originally just a big chunk of foam), and we re-routed a good number of the wires and cables.
One of the more interesting bits of construction, the touch panel was meant to mount to a much thinner panel, requiring the routing of the back side of the plywood panel with a 1/4" end mill. A couple layers of paint, and the center console was ready to show off at the open house and looks fantastic. Still to do is organizing all the wiring inside, and thanks to Amanda's mad sewing skills, a genuine viynl cover instead of paint. Also part of driver information/fit'n'finish is getting all the gauges working and looking stock.
Friday, August 7, 2009
Motor/speed reducer/differential assembly Version 2.0 is hanging from the lift; on the right you can see the motor controller (the black box) mounted in a polycarbonate enclosure (we went a little overkill on the waterproofing).
This photo is taken from inside of the engine compartment; you can see the clearance between the motor controller box and the top of the hood (the underside of the sheet metal) is about half of an inch.
The new motor frame, as seen above, clamped to the welding table - this is necessary to prevent the welding heat form warping the frame. This is version 2.0, which is slimmer and allows for the clearance to mount the motor controller next to it in parallel.
The components for the chain-drive speed reducer. From the left: flexplate adapter (connects the lower chain sprocket shaft to the differential); spline shaft and sprocket spacers (connects to the motor at the top); lower chain sprocket shaft with the lower bearing mounted and the other side of the triangular flex plate adapter.
Saturday, August 1, 2009
The choice between spending more time in front of a computer vs. spending time in the shop with a TIG welder usually favors the latter: we can't wait to get this car on the road.
Mike, welding the coolant pump mount to the frame rail.
Matt, machining the 1/2 inch thick aluminum walls for the chain drive enclosure. The bearing plates for this cannot be allowed to flex at all, otherwise the chains (we're using 4 in parallel) will become unevenly loaded, leading to a cascading failure after the first chain snaps.
Arya, about to mount the wiring harness/interconnect box.
The motor / diff frame assembled and mounted in the car. A 1.7:1 ratio chain drive connects the two. This is our first iteration of this frame; currently we're working on the second one, that will be slimmer at the bottom and slightly offset to the left, to make room for the motor controller box.
A (very rough) mounting of the motor controller box. This will house the 640A, 400V controller electronics, and needs to be watertight. It's constructed from 1/4" polycarbonate, with a 3/8" sheet on the mounting surface of the controller. 1/2" thick polycarb is bulletproof.. It's waterjetted and dovetailed at the ends, which will be bonded and sealed with silicone.
Jigging up the motor/controller frame, version 2.0. This time we'll get it right . . . no warped joints, no flex, slimmer by 4.5" at the bottom, leaving more room in the engine bay for mounting other components and (future) battery modules.
The sponsor logos on the car, prepped for the open house (the shop was much cleaner for that event). We had the president, provost, supporting faculty and corporate sponsors stop by and attendance remained strong throughout the evening.
The custom 17-spline shaft for the motor is finally here. It was much cheaper to send the shaft out to be made via EDM (electrical discharge machining) rather than a conventional broaching method.
. . . more to come in the next few days
Wednesday, July 22, 2009
Friday, July 17, 2009
Today, we started dismantling the car at 9am. We finished removing the engine at 3am and were out of the shop at 3:30am. We completed all of the major dismantling in only one day. We took out the gas tank, the battery pack, the engine, and parts of the interior. Take a look at our blog to see a time lapse of the whole day! It is an awesome video!
Sunday July 12th: Final dismantling:
In the morning, I finished removing the rest of the things from the engine compartment and I rebolted the suspension in place so the car can roll. The car is pretty much entirely ready to have new parts installed in it.
Drive Train Revision:
Radu and I had a long talk in the morning about the drive train. The original plan was to put the motor in the exhaust channel under the car and then run a shaft up to the differential. This plan had a couple of serious drawbacks: first, we would have to invert the rear differential which could lead to lubrication problems; second, we would have to cut into the exhaust channel and do body work which is in general a pretty bad idea; third, we would be spinning the differential at 12,000 rpm when the car is going 100mph. After thinking about all these challenges, I thought up another way that we could do the drive train which will probably be a lot easier. My idea is to mount the motor above the differential and have a chain drive linking the two. The chain drive will give us a lot of flexibility with the gearing and the whole assembly will just sit where the old engine was. This plan solves all of the major drawbacks of the old plan but introduces a few new challenges. Mainly, the chain drive and all the mounting. Radu and I both really like the idea and we talked to the rest of the team about it and they also think it is a good idea. I made a CAD model of the whole motor/differential assembly in the evening and I plan to talk it over with the other guys tomorrow.
Monday July 13th:
Mike, Radu, Matt, and I had a long design powwow in the morning about the motor/differential mount. We decided that the best way to do the drive train is to rigidly mount the differential to the motor and then mount both of those to the car through the existing motor mounts and several anti-roll bars. Here is a picture of the CAD model that we finally settled on.
Tuesday July 14th: Motor Frame:
Today I assembled all the basic components of the frame and tack-welded them together. Cutting the compound angles on the cold-cut saw was a little bit of a challenge but Mike had a good suggestion to make angle blocks and it worked very well.
I spent several hours calling junk-yards and BMW shops in the area to find a differential that we can use. The Ford 9 inch differential that we have and were planning to use before is too big to fit in the car so we decided to look for another, smaller differential. Because our motor will be outputting so much power, we want a very strong differential so we decided on a BMW rear differential. We would like to get a Limited Slip Differential to improve our handling but it is not critical. I ended up finding a good used transmission at Nissenbaum’s auto salvage very close to the shop. I went over there and picked it up in the afternoon. The guys at Nissenbaum’s were very helpful and were very interested in our project.
Wednesday July 15th: Motor Frame:
Mike and I went in the morning and water-jet cut the front face of the motor mount. It took about 25 minutes worth of cutting time because the steel was 1/2” thick. I welded the entire frame together and fitted the motor and differential into it. The frame itself weighs about 50-60 lbs. With the motor and differential, the frame weighs about 400 pounds.
Thursday July 16th: Differential:
I degreased and repainted the Differential so it is protected and looks good. I sized, lined up, and drilled the hole to mount the differential to the front plate of the motor frame as well as the hole where the shaft goes through the front plate of the frame.
Motor & Differential Frame:
I finished welding the pieces that Matt made for the engine mount cross bar. The steel frame is mostly done. All that is left is to make the cover for the sprockets. Here are a few pictures of the frame. The differential is the black thing on the bottom and the motor is the aluminum cylinder on top. The third picture shows the frame placed in the car. This is how it will look when everything is mounted correctly. The box on the end of the motor is the oil sump. It holds the extra cooling oil from the motor and fits very nicely in the old exhaust channel.