Volkswagen’s World’s Most Efficient Car: The XL1 Diesel Hyrbid

Volkswagen made a press release recently about another milestone reached by their concept car  codenamed the XL1 . They seem to be so impressed with the vehicle’s performance that they are going all out and calling it the world’s most efficient car. Their diesel-electric hybrid vehicle was driven from the VW headquarters in Wolfsburg, Germany, to the location of the Annual Stockholders Meeting in Hamburg, Germany, by the Chariman of the Board of Management, Dr. Ferdinand Piech, with an average fuel consumption of only 0.89 liters per 100 km (60 miles). VW has made great strides in attaining their goal of producing a practical and roadworthy two-seater car running on diesel and able to travel 100 km on 1 liter of diesel fuel or 235 miles on 1 gallon. (Link to a PDF of the July 2011 newsletter here and a video release here.)

Here is a recent article on the XL1 with plenty of photos of the concept car which is only  3.97 m long (13 ft) x 1.68 m wide (5.5 ft) x 1.18 m high (3.9 ft), and weighs 795 kg (1,750 lb). The impressive fuel efficiency is achieved only with the help of advanced light weight materials (carbon fiber skin, magnesium frame) and effective aerodynamics (drag coefficient of 0.186, Cd of Hummer H2 is 0.57 and that of Toyota Prius is 0.25).

The aluminium monobloc engine consists of one half of a 4-cylinder 1.6 liter TDI turbo-diesel engine wherein the 800 cc 2-cylinder engine is mated with an electric motor and an automatic 6-speed electrical switch controlled gear box. The car has a top speed of 158 kph (99 mph) and does a 0-100 kph (0-60 mph) in 11.9 seconds.

While this is only a concept car and not yet fit for production, it nevertheless underscores the usefulness of the diesel engine for the present day as well as for the future. We have certainly come a long way from when Mr. Rudolf Diesel demonstrated his first engine on peanut oil at the World’s Fair in the year 1900.

While diesels have always been more efficient than gasoline engines, these days are also clean and fast (Anyone remember the diesel Formula 1 engine?). Most modern diesel engines are based on the common rail fuel injection system that employ piezo-electric fuel injectors that inject a small spray of fuel directly into the engine cavity at a whopping 26,000 psi (1800 bar) of pressure. (Gasoline direct injectors are rated at about 2000 psi or 140 bar.) This allows the precise and metered dosage of fuel to be added at just the right time. The high shear rates at such extreme pressures ensure that the fuel exits as a fine mist with very small droplet sizes (about 50 micrometers or less) which enables a thorough and clean burn.

Another advantage of diesel is something that Mr. Rudolf Diesel himself foresaw but never realized in his generation because petroleum based fuels overtook the market and that is the use of bio-diesels. Bio-diesel is formed when an alcohol (e.g. wood alcohol/methanol or ethanol) is reacted with an oil (vegetable or animal based) in a process called trans-esterification. It seems so simple and , apparently, it is because for more than a decade many private citizens in the US and elsewhere have been producing and selling their own bio-diesel made from waste cooking oils collected from restaurants. The restaurants want to get rid of their waste oil which cannot be poured down the drain as it clogs up the pipes. The fuel producers get paid to take the oil away and turn it into fuel. In addition, bio-diesel is cleaner for the engine and has superior lubricating properties than petro-diesel. It is a win-win for everybody.

McDonald’s in Dubai has decided to capitalize on that idea and turn their waste cooking oil into fuel to power their delivery trucks. All that talk of bio-diesel makes one hungry. I am craving a big, juicy burger and a large plate of fries right now.


About propulsiontech

Propulsion technologist, aerospace engineer
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