Natural Gas (CNG, LNG) and Autogas (LPG)
• Comparatively clean burning process
• Commercialisation of CNG could pave the way for other gaseous
fuels such as biogas (biomethane) and/or hydrogen
• CNG could be mixed with biogas (biomethane)
• Comparatively clean burning process
• Is easily available at low costs
• Commercialisation could pave the way for other gaseous fuels
• Natural gas and LPG are based on fossil feedstock
• Availability of natural gas: transport sector might have to
compete with other sectors; Europe might have to compete with other
regions (China, India)
• Could a gaseous infrastructure pave the way to a so-called
• To what extend does CNG or LPG open the way for a market
penetration of Biomethane or DME and, thus, serve as a keystep on the
way to clean fuels.
Source and characteristics
The central difference between Natural Gas and Liquefied Petroleum Gas
(LPG) is that Natural Gas can be found in nature whereas LPG is an
artificial by-product from refining processes or can be extracted from
natural gas. LPG, also called Autogas, is a mixture of butane, propane
and low amounts of other gases. It commonly fuels Otto ICEs but can
also be used in diesel engines.
Further, it is important to note that LPG, propane and butane are
"automatically" generated during the extraction of natural gas and the
processing of methane. So, there is some flexibility in terms of
Natural gas can often be found beneath oil basins. It is a gaseous
fossil fuel consisting primarily of methane (CH4). It nearly needs no
processing for the use in automobiles which is a decisive advantage in
terms of feasibility. The actual composition of Natural Gas may vary
widely between countries, depending on the gas origin. Since the
energy density of natural gas is low compared to diesel, the fuel has
to be stored in compressed form as so called Compressed Natural Gas
(CNG) or liquefied (LNG) at a very low temperature of -161°C.
Accordingly, LNG offers a higher energy density than CNG, but CNG is
much easier to handle.
CNG can be transported in pipelines over long distances; the transport
of LNG in specialised "reefer" vessels becomes more and more common
but is comparatively costly. In terms of security the storage of both
CNG and LPG is not dangerous.
Autogas can be compressed to a liquid at very low pressures. In this
form it is used in conventional spark-ignition engines with only small
alterations. The main modification required is the provision of an
alternative fuel tank and supply to the engine (STEPS, 2005). Both
Natural gas and LPG offer high octane ratings.
Deliverability, competitiveness and contribution to energy security
The natural gas and LPG pathways are already commercialised and
compete with each other as well as with conventional gasoline engines
– even if market shares in the EU are (still) marginal. Especially
bivalent CNG-cars which can be powered by conventional fuels as well
as by CNG have the potential to increase market shares quickly. For
example the Opel Combo CNG has a 200 bar CNG-tank which allows a range
of about 360 km. If CNG runs empty the vehicles switches automatically
to gasoline which is stored in a 15 litre tank and provides for
another 150 -170 km. Driving performance of both fuels is equal.
"There are more than 4.7 million natural gas vehicles (NGVs) in
operation around the world today; nearly 557,000 in
Europe alone. These include passenger cars, light vans, delivery
trucks, garbage trucks and urban buses" (ENGVA 2006;
Concerning the market diffusion of CNG and LPG, the situation in
Europe is not homogeneous. A crucial factor is the number of existing
filling stations. In order to enable a successful transition to a
mass-market product CNG and LPG need a dense network of filling
stations. Whilst LPG is rather widespread in several European
countries, CNG filling stations might be hard to find in many regions.
In addition, stations are often situated in larger cities or in
industrial areas but not along the highway network. On the other hand,
there are countries such as Portugal, Italy and Germany where a
relative dense network of CNG-fuelling stations is currently emerging
(see figure 8). For example in Germany the energy supplier E.ON
announced in autumn 2006 that it will build 150 CNG pumps at filling
stations along German Highways.
Many observers see natural gas as the next dominant fossil fuel on a
global scale. From the supply side, a coverage of, for example, 10% of
general fuel demand by CNG would not add too much to the overall
consumption of natural gas in Europe. On the other hand CNG-
contribution to the energy security is clearly restricted by the fact
that natural gas is a fossil
resource which is not available endlessly (see DWV 2006, 12). Natural
Gas and also LPG are imported to a large extent in the EU from
politically sensitive regions which significantly reduce their
potential contribution to Europe's mid-term energy security. A large
scale use of natural gas in the transport sector would lead to an
overall increase in demand which has to be satisfied – at affordable
prices. Furthermore, if you consider the phasing out of coal and
nuclear power, the overall demand for natural gas is expected to grow
strongly. Transport has to compete with the generation of electricity
Regarding LPG the JRC study points out: "The net effect of an increase
in the use of LPG for automotive purpose would be to increase
imports." (JRC, 2006, 30). Of course, the same is true for natural
gas. LPG is popular because of its usually low costs. Currently
several automakers (Citroen, Daewoo, Fiat, Ford, Peugeot, Renault,
Saab, Volvo and others) sell models
equipped with bi-fuel models that run equally well on both LPG and
gasoline. It is comparatively simple to retrofit a vehicle with LPG
equipment. In most cases LPG vehicles are bivalent which allows them
to drive on both, petrol and LPG.
stations are rather widespread in Europe and that around 4.4 million
vehicles are fuelled with
LPG. However, as the STEPS report states, "the penetration on the
total vehicle fleet of LPG
has limited chances, given the nature of the resource itself, which
may be seen either as a
"surplus" in upstream oil production or as a by product of refining."
An important detail: Both LPG and natural gas vehicles are exempt from
the London congestions charge. The mid-term effect of such regulations
should not be underestimated. If similar regulations are applied to
other European cities, market penetration of those fuels might become
Energy balance, emissions and contribution to climate security
As a fossil fuel, CNG and LPG face similar problems as oil: they are
finite resources and contribute to global warming. The advantages of
natural gas as a fuel are the comparatively clean burning process and
the low content of carbon. Significant reductions of particulate
NOx and CO emission are possible. Related to GHG emissions, balancing
is not easy and depends on various factors. The JRC (2006, 4)
comments: "The WTW GHG emissions for CNG lie between gasoline and
diesel, approaching diesel in the best case". The same study estimates
that beyond 2010 GHG-emissions become lower than those of diesel since
greater engine efficiency gains are predicted for vehicles equipped
with engines that are optimised for the use of CNG. The STEPS report
points out (2005, 51): "Natural Gas has nearly zero sulphur level and,
thus, negligible sulphate emissions, while causing low particulate
emissions because of its low carbon to hydrogen ratio. Evaporative
emissions are low too, requiring little control.
Due to its low carbon-to-hydrogen ratio, it produces less carbon
dioxide per GJ of fuel than either gasoline or diesel. However,
exhaust emissions of methane, which is a greenhouse gas, are
relatively high. It has low cold start emissions due to its gaseous
state and a superior antiknock behaviour due to its high octane
factor, thus allowing higher compression ratios, favouring engine
efficiency and operation under turbocharged conditions".
Primarily because of the lower carbon content LPG induces less exhaust
emissions than petrol. Also on a WTW-basis, CO2 benefits of LPG are
significant compared to those of petrol.
LPG's well-to-wheel energy consumption falls below that of gasoline
but above that of diesel (STEPS 2005). Regarding WTW energy and GHG
emissions balance, the JRC study concludes for LPG coming from the
Middle East: "LPG's GHG emissions lie between diesel and CNG and
energy between gasoline and diesel. Although not explicitly shown in
transport distance has a significant impact, representing about 25% of
the WTT energy in this case" (JRC, 2006, 30).
Additional Applications and pathways
Both, CNG and LPG, can be mixed with biomass derived gases (Biogas and
DME; see Biofuels section)
Blends of hydrogen and natural gas are discussed and tested (see
CNG technology is feasible in the transport sector and has the
potential to bring at least mid term improvements in terms of energy
security and GHG emissions – whereby it is crucial that real
"gas-engines" are being developed. But in particular its possible
contribution to energy security strongly depends on the overall demand
on natural gas. It is likely, that CNG
vehicles will become at least established for niche applications (e.g.
in larger fleets, in inner cities). LPG is a relatively uncomplicated
technology. It offers environmental benefits at relatively low costs.
It is becoming rather popular in several European countries. Since
both, CNG and LPG, are based on fossil feedstock they must be
considered as bridging technologies. They might help to pave the way
for "cleaner" gaseous fuels such as hydrogen, biomethane or DME.
"The paradigm shift from liquid to gaseous fuels will create enormous
new business opportunities—initially mainly for methane-powered
vehicles, but eventually also for hydrogen fuel cell vehicles" Peter
Boisen, former Volvo executive and chairman of ENGV Europe; quoted in
Tuesday, December 4, 2007
CNG in EU Report on Alternative Fuels
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