|The eco up! natural gas vehicle. Click to enlarge.|
Volkswagen has launched the eco up! natural gas vehicle, previewed in a concept form in 2011 (earlier post) and revealed in its production version at the Geneva auto show in March this year, in Europe. The four-seat Volkswagen with its 1.0L engine consumes 2.9 kg (4.4 m3) of natural gas per 100 km—equivalent to CO2 emissions of 79 g/km. The 50 kW (67 hp, 68 PS) eco up! was rated in the best energy efficiency class: A+. In Germany, the car, even before market launch, was picked as the overall winner in the VCD Environment List (VCD Auto-Umweltliste) and was also awarded the ACVmobile environmental prize (ACVmobil Umweltpreis).
Engine. For the eco up!, Volkswagen used a newly developed three-cylinder gasoline engine with 999 cc displacement (EA211 engine series). The natural gas version produces its 50 kW output at 6,200 rpm and reaches its maximum torque of 90 N·m (66 lb-ft) at 3,000 rpm. The eco up! accelerates from 0 to 100 km/h in 16.3 seconds; its top speed is 164 km/h (102 mph). Although the 12-valve engine was specially configured to operate with natural gas, as an alternative it can be fueled with unleaded premium gasoline.
Like the gasoline engines of the up!, the natural gas engine, which is closely related technically, is also made of aluminium. The two overhead camshafts are driven by toothed belts; the intake camshaft is variable, further reducing emissions and fuel consumption and improves the power curve in the lower rev range. The valves are activated by cam followers with very low friction. The engine’s dual-circuit cooling system and integrated water-cooled exhaust manifold enable short engine warm-up times. Each cylinder is equipped with a separate ignition coil.
Configuring the new three-cylinder MPI engine for CNG operation required several modifications. To compensate for the somewhat poorer filling of the combustion chambers in λ1 operation, the engine’s compression ratio was increased from 10.5:1 to 11.5:1. The spark plugs also supply a higher ignition voltage for the higher pressures and combustion chamber temperatures caused by the earlier ignition timing.
Other modifications relate to materials used for the valves, their guides and seat rings; they compensate for the lower lubricating properties of gaseous fuels; the cam contour was also modified. Meanwhile, the variable intake camshaft was modified for the lower residual gas compatibility in CNG operation.
The use of precious metals in the catalytic converter and their composition were also reconfigured, as when natural gas is combusted, about 25% less CO2 is generally emitted with far less carbon monoxide and hydrocarbons. Soot and fine dust are not even emitted. However, any unburned methane must be converted in the catalytic converter.
The engine controller was also modified in the eco up! to handle management of the gas injection valves and the electronic gas pressure regulator. The operating mode indicator and the fuel economy and tank level gauges in the instrument cluster are also based on engine controller computations.
Via the oxygen sensor, the engine controller also detects the different qualities of “low” and “high” gas, especially those that appear on the German market. When operated with low gas, the calorific value of which is lower due to its lower methane content, the fuel injection time is adjusted accordingly.
The electronic gas pressure regulator has been used in a similar form since 2008 in the larger CNG models from Volkswagen. The new version for the eco up! is extremely compact and lightweight with about 0.2 liters volume and about 600g in weight. It is mounted to the engine subframe behind the right headlight. The electronic gas pressure regulator reduces gas pressure from 200 bar to the low pressure system’s operating pressure of 4 to 9 bar in two stages. In the first stage, the pressure is reduced to 20 to 25 bar; in the second stage it is then electronically regulated to the target pressure.
Since reduction of the natural gas pressure leads to cooling, very low temperatures may occur in the electronic gas pressure regulator. To prevent potential icing here, the component is incorporated into the engine coolant loop, which heats it with hot coolant. Variable control of the natural gas pressure to 4 to 9 bar offers tremendous advantages—in the upper load/speed range, the gas flows into the combustion chambers at maximum pressure to achieve highest torque or full power. On the other hand, a pressure of 4 to 5 bar is sufficient in the lower and mid ranges.
From a coolant temperature of -10 °C (+14 °F) upwards, the eco up! engine is started with gas; at lower temperatures it is started with gasoline. After filling the natural gas tank, the engine also runs on gasoline for a brief time period; it does not switch over to gas until the oxygen sensor has been activated, and the gas quality (L or H) has been analysed to determine the correct opening times of the injection valves. As soon as the adaptation is been made, the engine is started with gas with each restart.
In addition to the engine, the fuel economy and emission values of the eco up! are supported by its low curb weight (1,031 kg/2,273 lbs); aerodynamic properties (Cd = 0.32; frontal area = 2.07 m2); standard BlueMotion Technologies (Stop/Start system, battery regeneration, low rolling resistance tires); and an efficiently operating engine-gearbox-combination.
Tanks in the underbody. The natural gas is stored in two subfloor tanks (total capacity: 72 liters / 11 kg CNG) near the rear axle. Tank number 1 (35 liters) is located in front of the axle together with the reserve gasoline tank (10 liters); meanwhile, tank number 2 (37 liters) utilizes the space of the spare wheel recess. Since the entire EcoFuel system could be integrated entirely within the vehicle structure, usable space is not restricted in any way except for the lack of a spare wheel recess. The port for refueling the eco up! is located behind the same fuel door as the gasoline filler neck.
With full tanks, the new eco up! has a driving range of 380 km (236 miles) with just the natural gas; the gasoline in the reserve gasoline tank adds another 220 km (137 miles) of driving range. So, a total of up to 600 km (373 miles) can be covered with a single fill of the tanks.
A tank gauge in the instrument cluster indicates both the natural gas and gasoline fuel levels, and the remaining driving ranges of both operating modes are shown in the multifunction display. In Germany, there are currently 911 natural gas refilling stations (as of October 2012). There are well-distributed supply networks in many other countries in Central Europe as well. Today, there are also a number of apps and navigation system extensions and Internet portals that specifically reference natural gas refilling stations.
(In Germany, the fuel cost per 100 km (62 miles) is just over €3 (US$3.92); in Italy, the largest market for natural gas cars in Europe, the cost is less.)
The eco up! is offered in three trim levels.
Volkswagen now (he end of 2012) offers six natural gas powered vehicles in various classes: the Caddy 2.0 EcoFuel; the extended Caddy Maxi 2.0 EcoFuel (each 80 kW / 109 PS); the Touran 1.4 TSI EcoFuel; the Passat and Passat Estate 1.4 TSI EcoFuel (each 110 kW / 150 PS); and the eco up!. In the upcoming year, the new Golf will also debut in an EcoFuel version. In this vehicle,
Biomethane and e-gas. The natural gas vehicles can also be powered by alternative fuels such as renewable biomethane, Volkswagen notes. Produced from plant by-products, biomethane does not compete with food crops; it is also CO2-neutral, because the car only emits as much carbon dioxide in combustion as it absorbed while the plants were growing.
By mid-2011, there were 57 biomethane plants in Germany, which fed 64,000 standard cubic metres (std. m3/h) into the natural gas network per hour. Today, biomethane is blended at one-fourth of the available natural gas refilling stations in Germany; in addition, nearly 100 stations already offer pure biomethane—currently the most of any country.
Volkswagen points to technology leader Verbio AG, which has developed a new type of bio-refinery that produces biomethane exclusively from stillage (a waste product of bioethanol production), and straw. Verbio AG has also been operating the first facility for producing biomethane exclusively from straw since February 2012.
Gas also offers the opportunity of storing electrical energy from renewable sources such as wind power. This involves producing hydrogen by electrolysis, which can be used to operate future fuel cell vehicles. The hydrogen can also be used to produce methane in a second step of the process chain—i.e., Audi’s e-gas project. (Earlier post.) In turn, the methane can be used as a fuel for cars such as the new eco up!.
Together with a number of project partners—such as SolarFuel GmbH and the Centre for Solar Energy and Hydrogen Research (both in Stuttgart), the Fraunhofer Institute for Wind Energy and Energy Systems Technology (Kassel) and EWE Energie AG (Oldenburg)—the Volkswagen Group is further developing the e-gas process.