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Gas in the fuel tank – an alternative fuel to diesel and petrol

Natural gas mobility

Natural gas as an alternative fuel can help to reduce CO2 and other transport-related pollutant emissions quickly and cost-effectively. Natural gas vehicles are far more eco-friendly than vehicles powered by petrol and diesel and as such offer an alternative that can contribute substantially to protecting our climate. The technology exists; it is field-tested and suitable for daily use.

Gas in the fuel tank – an alternative fuel to diesel and petrol; © candy1812/Fotolia.com

Gas – a climate-friendly fuel

An affordable fuel that helps to keep the air clean

Anyone contemplating how to find efficient and socially compatible ways to protect our climate, control air pollution and achieve sustainable mobility cannot ignore the potential of gas as a transport fuel. As gas has significantly lower emission values than diesel or petrol, it can make a decisive contribution to meeting the climate protection targets set for the transport sector when used as an eco-friendly, alternative fuel. Natural gas-powered vehicles also have indisputable advantages over their petrol or diesel-powered competitors with respect to nitrogen oxide and particulate matter emissions - topics that are currently hotly debated. The required technology exists; it is field-tested and mature. The DVGW is largely responsible for preparing the safety-related technical set of rules for natural gas filling stations and natural gas-powered vehicles in Germany and is actively involved in the preparation of national (DIN), European (CEN) and international (ISO) standards.
Gas in the fuel tank – an alternative fuel to diesel and petrol
Natural gas – a clean and affordable alternative fuel
Natural gas – a clean and affordable alternative fuel © Soloviova Liudmyla/Fotolia.com

Back in the 1990s, an environmentally friendly alternative to petrol and diesel cars established itself on German roads: Cars powered by compressed natural gas (CNG) were becoming increasingly important as they emitted far less pollutants. Being less expensive and cleaner than conventional fuels, compressed natural gas suggests itself as an alternative fuel especially for private transport.

The heavy-duty road transport sector – which is of particular significance for Germany, the hub of European trade - can also rely on a forward-looking drive technology: liquefied petroleum gas (LNG). In other European countries as well as outside Europe, LNG-powered trucks have ceased to be a rarity and successfully hit the roads. As LNG combines long-haul capability with low pollutant emissions, experts expect the use of LNG to rise also on German roads.

However, businesses need unambiguous political signals that ensure planning and investment security as well as support in building an infrastructure of natural gas filling stations so as to be able to fully exploit the climate protection potentials offered by natural gas-powered mobility and to accelerate its market entry.

Gerald Linke, Managing Director of DVGW

Gas goes green – future mobility
Audi’s power-to-gas system in Werlte generates green gas from wind
Audi’s power-to-gas system in Werlte generates green gas from wind © Audi AG

An intelligent, eco-friendly mobility that takes into account the specific transport application, the mileage to be covered and the goods to be transported requires the harmonious interaction of different technologies. Widely differing applications in the transport sector call for optimal solutions that are economical and sustainable at the same time.

The so-called fuel switch, i.e. the substitution of diesel and petrol with gas as an energy carrier, is a first step by the transport sector towards achieving climate protection effects quickly and efficiently. Electro-mobility still has a long way to go until it is ready for series production; a charging infrastructure has not yet been rolled out nationwide, and a significant share of the German power mix is generated on the basis of coal - the latter one being particularly to blame for the fact that electric cars and trucks will not be able to make a tangible contribution to climate protection in the transport sector within the foreseeable future – and therefore cannot be expected to produce any significant climate or environmental effects in the short term.

Natural gas-powered vehicles, on the other hand, can help to immediately and significantly reduce CO2 and other pollutant emissions thanks to a mature and field-tested technology. What is more, the existing natural gas grid offers a perfect infrastructure that ensures the supply of natural gas throughout Germany.

Interaction of green gas and electro-mobility

In the medium and long term, both CNG and LNG need to be produced in a climate-neutral way. The technologies to achieve this goal are power-to-gas (P2G) and biogas plants, both of which make it possible to fuel passenger cars as well as trucks with renewable and greenhouse gas-neutral fuels sustainably generated from renewable resources and energies. “Green variants” can thus gradually substitute fossil-based CNG or LNG by way of a content switch, and they can also be easily integrated into the existing system.

This way, renewable gases would complement electro-mobility in the transport sector. The use of green gas would make most sense in those segments where electro-mobility can be utilised only insufficiently or not at all, e.g. in long-haul and heavy-duty applications on the road and at sea.

The biomethane generated from biogas serves as an environmentally friendly fuel
The biomethane generated from biogas serves as an environmentally friendly fuel © Wolfgang Jargstorff/Fotolia.com

Bio-natural gas generated from renewable resources, sewage sludge, manure or bio-waste presents another alternative of using renewable gas as a fuel. The so-called process of fermentation first generates biogas, which in a second step is upgraded to biomethane and/or bio-natural gas.

Even now, numerous filling stations offer 100% bio-natural gas for fuelling up natural gas cars, enabling them to drive with almost no impact on our climate. The combustion of bio-natural gas in the engine releases only the amount of CO2 that was bound in the natural material. Consequently, only the CO2 that was absorbed by e.g. plants during photosynthesis is released back into the atmosphere in this cycle.

Power to gas station – renewable gas generated from green electricity
Power to gas station – renewable gas generated from green electricity © Uniper Energy Storage GmbH

Green gas generated by the power-to-gas technology from surplus solar or wind-generated power has no negative climate impact at all when used as a fuel. Green power is electrolytically converted first to hydrogen, and then to methane. This allows for the conversion and long-term storage especially of wind power, which puts a burden on the electricity grid in stormy times.

Audi successfully operates a power-to-gas station in the town of Werlte in Lower Saxony. The plant generates renewable gas from green electricity and injects it into the grid as “Audi e-Gas”. The green and/or renewable gas can be efficiently stored in and transmitted through the gas grid and is therefore available for fuelling up natural gas cars everywhere.

Gas goes green – Mobility of tomorrow
Gas goes green – Mobility of tomorrow © DVGW

Biogas and power-to-gas plants are two technologies that have a huge potential to bring about a successful energy turnaround and to promote climate protection in Germany. Green and/or renewable gases can be efficiently stored in and transmitted through the gas grid, allowing natural gas cars to be fuelled up everywhere. The German gas grid with its length of more than 500,000 kilometres offers an ideal infrastructure for the nationwide and reliable supply of gas. Another big advantage in this context is that the self-same infrastructure can be used to supply gas to cars and/or filling stations as well as households, the industry and gas power plants. LNG, which can be filled in the tank either directly or can be re-gassed and injected into the natural gas grid, offers these sectors even more reliability of supply.

CNG, LNG, LPG and hydrogen – what are the differences?
Gas as a fuel falls in different categories:
Natural gas can be fueled quickly and easily
Natural gas can be fueled quickly and easily © Zukunft ERDGAS/Kai-Uwe Knoth

CNG (Compressed Natural Gas) denotes natural gas that is compressed at a pressure of 200bar to reduce its volume by approximately 1:200. Compressed natural gas consists mainly of methane and is used to power passenger cars and trucks. The CNG combustion process in the engine produces considerably reduced CO2 emissions as it is much cleaner than the combustion of diesel or petrol. The reduction of pollutants such as, for instance, particulate matter and nitrogen oxides, which pollute the air in conurbation areas, is even more substantial. As the gaseous CNG reaches the filling stations through the underground natural gas grid, it is available everywhere.

LNG is used mainly for heavy-duty long-haul transport
LNG is used mainly for heavy-duty long-haul transport © Volvo Truck Corporation

LNG (Liquefied Natural Gas), which is sometimes also called liquefied gas, should not be mistaken for liquid gas (LPG). LNG is a conventional natural gas that is liquefied by cooling it down to approximately -162°C. The concurrent reduction in volume by about 600 times allows tankers to transport large quantities of LNG by sea. As considerably larger quantities of LNG – compared to conventional fuels - can be stored in a vehicle fuel tank, it is used mainly for heavy-duty long-haul transport. LNG-powered vehicles can cover long mileages and, unlike diesel, emit far less CO2 and other pollutants.

LPG is often also called autogas.
LPG is often also called autogas. © Gerhard Seybert/Fotolia.com

LPG (Liquefied Petroleum Gas), which is sometimes also called liquid gas or car gas, is a mixture of butane and propane. It is generated as a side product during the production of petroleum and natural gas and originally occurs in the gaseous state. At room temperature it enters the liquid state even at low pressures of up to 8bar and can then be stored in bottles or tanks. Unlike natural gas (CNG), liquid gas (LPG) is not transmitted through the gas grid. Liquid gas is used for heating and cooking, but also for powering cars, in which case it is called “car gas”.

Liquid hydrogen is transported in tanks
Liquid hydrogen is transported in tanks © The Linde Group

H2 (hydrogen) is almost infinitely available on our planet. It occurs almost always in chemical compounds such as water and hydrocarbons (e.g. natural gas and petroleum). Thanks to its high energy density, hydrogen is used for generating energy, but it is also employed by the industry, e.g. for producing chemical ammonia-fertiliser or glass. Hydrogen may however also be used as a low-emission car fuel, powering either a conventional internal combustion engine or supplying a fuel cell, which latter converts the hydrogen to electrical energy that is then used to drive a downstream electric motor. All these applications have one thing in common, though: The hydrogen needs to be generated before it can be used, either by steam reforming natural gas or by means of water electrolysis, which breaks down water into hydrogen and oxygen with the help of electrical (renewable) energy.

Natural gas – protecting the climate and the environment
Nitrogen oxides and particulate matter exacerbate the air pollution problem in conurbation areas
Nitrogen oxides and particulate matter exacerbate the air pollution problem in conurbation areas © iStock.com/william87

CNG and LNG fuels can directly and quickly help to reduce CO2 emissions caused by traffic in Germany. The combustion of natural gas in the engine produces substantially less CO2 than the combustion of diesel.

When considering the entire value creation chain (well-to-wheel, i.e. all emissions produced from the start of production to the tank), the greenhouse gas reduction potential of natural gas for passenger cars is 25 per cent and 10 per cent compared to petrol and Diesel, respectively.

For trucks, the reductions amount to up to 22 per cent for LNG and 18 per cent for CNG.

Gas-powered cars – reducing CO2, nitrogen oxides, particulate matter and noise

But natural gas cars can do much more than markedly and sustainably improve the greenhouse gas balance within a short period of time. Used as an alternative fuel, natural gas can help improve the air quality quickly and sustainably, especially in inner cities where air pollutant limit values are increasingly exceeded and driving bans may be issued as a consequence. The clean combustion of natural gas produces about 70 per cent less nitrogen oxides compared to diesel engines, bringing particulate matter values down to almost zero. This way, natural gas-powered mobility does not only contribute greatly towards climate protection, it can also considerably reduce the burden of air pollutants in inner cities.

In addition, natural gas engines produce less noise than diesel engines and run much more quietly, so that the truck engines using CNG and LNG fuels emit only half the noise. These low noise emissions enable gas-powered trucks to deliver their cargo to inner cities even at night - e.g. when transporting fresh food to supermarkets.

Natural gas filling stations
An App helps to find a suitable natural gas filling station en route
An App helps to find a suitable natural gas filling station en route © Tomasz Zajda/Fotolia.com

About 900 natural gas filling stations currently exist throughout Germany, creating a nationwide infrastructure. Other European countries such as, for instance, Italy, also boast a good infrastructure of CNG filling stations, with Italy being the current European leader in CNG fuel supply.

Germany’s infrastructure needs to be extended further to ensure optimal supply and enhance the attractiveness of natural gas as an alternative fuel. Volkswagen and other partners announced that they would increase the number of gas filling stations in Germany to about 2,000 by 2025. A total of approximately 4,500 natural gas filling stations currently exist in Europe.

The partners listed below offer practical tools that help find CNG and LNG filling stations: