Volkswagen Magazine

THINK AHEAD

the third pillar.

Natural gas is a fuel with a future: sustainable, economical and convenient. Reason enough for Volkswagen to considerably expand its range of TGI models. A report on the past, present and future of natural gas-powered cars.

Text Kay Dohnke
Infographic C3 Visual Lab

The world used to be pretty simple. Petrol stations had diesel, normal and super petrol – and that was it. But today?
In addition to different variants of diesel there are E10, super, super plus, bioethanol and other products such as Ultimate, Extra and Performance on offer. It is also becoming more and more common to see natural gas – a fuel with a lot of potential for the future.


The age of natural gas as an automotive fuel has just started to rev up. This “juice” for specialised cars has now become a fully fledged, widely accepted option with its own unique advantages. Volkswagen has been working since 2002 on optimising the drive systems in the cars and engines that will form this third pillar.

“Because the combustion process for natural gas releases about 25 percent less CO2 than petrol, the cars that it powers are a good, environmentally responsible choice,” observes Dr. Heinz-Jakob Neusser, Member of the Board of Management for the Volkswagen brand in charge of developing drive systems.

 

This CNG (compressed natural gas) should not be confused with LPG (liquefied petroleum gas) even though the latter, which is a direct by-product of petroleum refinement, is known as “autogas”. LPG systems require fewer technical modifications, but LPG has only about half of the energy content of CNG – its consumption figures are around 20 percent above those of a petrol engine and its CO2 emissions are only a little lower. By contrast, CNG is classified by the EU as an “alternative” energy – just like hydrogen and electro-mobility.

From niche to mainstream.

Natural gas vehicles from Volkswagen did in fact arise as niche products. The first was the Golf IV. The engineers started by determining which models were best suited for integrating the requisite fuel tanks, which were initially located in the car’s interior. The positive response to the first natural gas Golf – Volkswagen R GmbH has made several thousand of these cars – prompted the developers to expand the gas-powered drive concept. Introduction of the PQ35 platform made it possible to put gas tanks into the Touran and Caddy as well – in a space-saving location in the underfloor. “Ever since then we’ve been considering natural gas as a possibility right from the start,” says Dr. Jens Arik Almkermann, director of development for natural gas tank systems at Volkswagen. Where is the best place to put these tanks without taking up any valuable space in the interior? What special requirements need to be met in order to give car models a natural gas-powered engine?

The natural gas market in Germany.

Development has been following two parallel tracks. While car designers have been working on where to install the tanks, engine developers have been optimising the drive systems to run on natural gas.

Petrol if needed.

Generally speaking, any combustion engine can run on natural gas. However, a number of technical modifications are needed to give drivers the full range of performance benefits and to ensure a long service life for the vehicle. Natural gas has a more favourable ratio of hydrogen to carbon than petrol. On the one hand, this means that it releases around one quarter less CO2 when burned – which is good for the environment. On the other hand, however, its higher octane level gives it an earlier firing point, which places greater strain on the components.


The developers have therefore been working on optimising valve, piston and crankshaft operation as well as the exhaust gas turbocharger or catalytic converter, and also on adding a few special parts such as a gas pressure regulator, gas injector valves and sensors. They have also modified the control unit so it can cover both gas and petrol modes of operation. All of Volkswagen’s natural gas vehicles are “bivalent”, which means they can also be driven on petrol.
If needed, the control unit switches imperceptibly from one type of operation to another, for example to petrol at very low temperatures and then back to gas when the injector valves warm up. It also switches from gas to petrol when the gas tanks are empty.

Two types of tanks.

The gas tank: Another important item. Special high-pressure tanks are needed for this natural gas, because it is stored at pressures of 200 bar. Two types of tanks are available, with walls made of steel or of a composite CFRP/GRP material. “Steel tanks can have thinner walls but they weigh more,” explains Almkermann. “From the standpoint of optimising lightweight construction, therefore, composite materials with their thicker walls come out ahead – but the savings in terms of weight mean a certain reduction in tank volume.” All the tanks have to meet the very highest safety standards, and all of the tanks developed by Volkswagen go through an extensive testing programme before entering series production.

How far will one pound take me?*

Natural gas enjoys a special advantage when it comes to sustainability. Not only does it have lower CO2 emissions, but it also releases no particulate matter in the combustion process. It can also make use of excellent supply conditions, with natural gas lines extending throughout every part of the country. In other words no independent infrastructure is needed for distribution, just the right type of pumps at the stations. And in theory, natural gas can be easily produced just about anywhere. The power-to-gas process developed in the Volkswagen Group by Audi, for example, produces hydrogen from renewable energy – that is, from wind or solar power, via electrolysis.

The hydrogen is then methanised with CO2 from biogas plants to produce natural gas – a process that can be run nearly anywhere and that performs well under test conditions, although is currently still costly.
When natural gas vehicles are fuelled with biomethane generated from agricultural or organic waste, they emit an impressive 97 percent less CO2 – an absolutely top figure. “Gas-powered systems offer two very attractive opportunities to us as developers,” observes Almkermann. “We can make driving more fun by making the engines more powerful, while at the same time making them more environmentally friendly by considerably lowering their emissions levels. Where else do you find this type of combination?”

Major market readiness.

In addition to environmental friendliness, low operating costs are also a factor in the successful equation. Drivers of natural gas vehicles pay about half the cost for the same driving distance. First of all, natural gas is considerably cheaper, and furthermore its consumption figures per kilo are lower than the figures per litre for petrol or diesel. On top of that, natural gas vehicles enjoy tax advantages.
As a consequence of all this, new car registration numbers have been rising substantially now for years. “Sales of natural gas vehicles have increased in recent years – by about 50 percent from 2012 to 2013 for Volkswagen alone,” reports Neusser. “With nearly 100,000 vehicles in Germany we’re well on our way.”

CO2 emissions

in g/km CO2 equivalent

One reason for this could well be the fact that the chicken-and-egg problem has been solved. In terms of natural gas that means as long as there are not enough models on the market, the gas industry is reluctant to invest in comprehensive distribution. And without this type of infrastructure, consumers are reluctant to take the step of buying a natural gas vehicle. But this dilemma has now been resolved, with rising numbers of both fuelling stations and new car registrations.

 

TSI, TDI, TGI.
The fact that ever more Volkswagen drivers are pulling up to natural gas pumps is also a result of greater product diversity. Volkswagen is setting a future-oriented course with its Modular Transverse Matrix (MQB). Vehicles from this platform all have sufficient space to incorporate natural gas tanks. Although only 14 natural gas vehicle models from different manufacturers were available on the market in 2012, that number increased to 24 in 2014. Around 40 models from the Volkswagen Group alone – across all vehicle classes – are potential candidates for natural gas operation.

The largest natural gas reserves in billions of cubic metres

 

“The natural gas engines used to be primarily in the lower and medium performance sector – based on customer need – from the eco up! with a 1.0-litre displacement and a 50-kilowatt output to the 1.4-litre twincharger engine with a 110-kW output”, says Almkermann.
Volkswagen has long since incorporated natural gas engines into its brand strategy. Special models have become standard series models, and the EcoFuel designation has now become the streamlined abbreviation TGI. In addition to TSI for petrol and TDI for diesel engines, TGI now forms the third pillar for combustion engines. And the variety of models to come will generate an additional surge of success.