Natural Gas Vehicle (NGV) engine technology is mainly based on a
well-known and already established engine functioning principle,
the Otto engine. The recent developments achieved and the OEMs push
for this kind of technology clearly shows the confidence and
reliability of this technology, especially when it comes to the use
of compressed natural gas (CNG). For the above-mentioned reasons,
the number of applications involving NGVs has increased
worldwide.
Environmental and economic reasons, on the whole, have been the
main drive for this diffusion. Natural Gas chemical properties are
an irrefutable proof of the advanced behavior, environmentally
speaking, of a fuel that emits less CO₂ (due to its carbon-hydrogen
balance when compared to other fuels) and less NOx and PM. In many
countries, favorable taxation schemes have helped the development
and entrance into the market of the NGV technology, especially for
the light-duty vehicles. Until now, practically no heavy-duty
vehicles or lorries have taken advantage of this fuel, because of
payload restrictions, and due to the cylinders weight required for
a suitable range, an issue requested by specific commercial mission
profiles.
Nevertheless, Liquefied Natural Gas (LNG) offers the possibility
of using this fuel for heavy-duty road transport applications due
to its higher energy density. It should be taken into account that
a temperature of -162°C is required (at atmospheric pressure) to
maintain the fuel in liquid state, therefore the main issue of this
technology lies on the cryogenic tank installed on board with a
thermal behavior control system and the board vaporizer required to
feed the internal combustion engine (ICE). This aspect (on board
cryogenic vessels) and some others like the refueling
infrastructure still require some standardization work, aspect that
is being developed at ISO level.
In this context a new interesting opportunity arises with
regards to the refueling infrastructure, that is the L-CNG filling
stations concept.
This application could be used by all types of natural gas
vehicles since it's able to deliver both LNG and CNG.
The gas in compressed form in this case is obtained from a
liquid cryogenic pump at 300 bar followed by a downstream
vaporizer, which releases gas in compressed form at 200-250 bar. In
this way, a reduced amount of energy is required, when compared to
the usual filling stations operated by compressors to build up the
CNG from the piped gas.