The one liter per hundred kilometer car project was introduce to the public in 2002 when Volkswagen's CEO drove the completed prototype from Wolfsburg to Hamburg coming in better than the design goal with a nearly 300mpg run.
The Concept
The L1: A prototype for production.
The XL1 into Limited Production
Performance Speculation
The idea for the one liter car project was for a highway cruiser that was safe and compatible with current traffic conditions while still being able to go 100km on a liter of fuel. The working prototype used a 300cc single cylinder diesel engine rated at just 8hp continuous output. With a very lightweight custom built carbon fiber chassis and body the working prototype looked extremely expensive and while it did deliver the performance it was intended to it did not look like something that was going into production. With just 8hp on tap it probably hardly went fast enough to be considered a highway cruiser at all, but then there is no minimum speed limit on the german autobahn system. Back then in 2002 I estimated that the svelt looking little car would probably go about 55mph on the 8hp which would have yielded about 110mpg peddle to the metal. To get the 270mpg that was claimed for the Wolfsburg to Hamburg run on the Autobahn I guessed that the car was driven at 30 or 35mph.
In 2009 a new concept car was shown at the Frankfurt Auto Show that was supposed to be a forerunner of a production one liter car. This new version used an 800cc two cylinder turbodiesel for much brisker acceleration and higher cruising speeds, but one liter per hundred kilometers was still claimed. The new car was considerably larger and heavier, but did have a provision for a passenger seat off to the side of and somewhat behind the driver’s seat.
The initial date for production vehicles to arrive on showroom floors was 2013, but this was continually pushed back year after year. The finalized design was released in 2011 with blistering acceleration from a 47hp 800cc two cylinder turbodiesel and an electric booster motor rated at 27hp. The new concept was a plug in hybrid where the battery would not be charged directly from the diesel motor, although regenerative breaking would keep the battery up if heavy acceleration was only infrequently used. For many years Volkswagen was very vague about the fuel consumption claims of this new hot rod of a small car. When a German car magazine finally got a hold of an XL1 this year the smoke was cleared somewhat. The claimed 260mpg (0.9l/100km) in the NEFZ highway fuel consumption test also uses 7.2 kWh of electricity per 100km when the car is plugged back into the electrical grid. Producing that 7.2kWh of electricity with a diesel generator would take no less than a half a gallon (1.9l) of fuel. The magazine also tested the fuel consumption without plugging the XL1 in and reported 87mpg(2.7l/100km) for a city, highway and autobahn loop. What they did not bother to mention was how fast they drove on the autobahn or what percentage of the miles was in each of the three types of driving. The XL1 is said to be able to go 100mph on the 47hp diesel engine, but at that speed fuel mileage might be less than 40mpg.
What is clear is that the Volkswagen XL1 is a smaller and lighter car that is still capable of going very fast. The capability for very high speed driving inevitably cuts into fuel mileage at lower speeds, but a lot better than 87mpg should be possible. It is not clear how well the current version of the Volkswagen XL1 can do in moderate speed highway cruising at 35 to 50mph, but a vehicle that can attain 100mph on less than 47hp is quite slippery. That same body shape should allow about 35 or 40mph cruising on just two horsepower. If the diesel engine can be made to run over a wide enough range of speeds and loads and the drag of the transmission and wheel bearings can be controlled the 300mpg of the original prototype would be attainable. What should also be kept in mind is that a full size four door sedan could also potentialy attain 300mpg at an even lower speed, but the larger car would also tend to not be able to attain as high of a top speed. The wider the range of loads over which the engine can attain high efficiency and the better the transmission and wheel bearings can do at radically reduced speed the higher the top speed would be for a 300mpg car. For more on transmission and wheel bearing efficieny see Fuel Hogs.