Abstract
Up to now in Europe we have seen the development of Standards and applications for the use of CNG in vehicle propulsion systems, as below: CNG (R110.00 ECE or ISO 15500 Series), Retrofit Kits (R115.00 ECE) The availability of standards to certify the applications has lead to a large number of vehicles running on gas, from the small vehicle to the urban bus and public service truck. The use of these vehicles has allowed us to gain great experience in their operation and enormous benefits has been obtained from the environmental point of view. However, all of these vehicles have a common problem; their range, since the low energetic density of Natural Gas means a lot of space is needed to store it, and also the gas cylinders are heavy and limit the payload. Vehicles running on Natural Gas have low range and are fully dependent on the availability of gas refuelling stations. To increase the range of the vehicles to almost the same level as vehicles running on petrol or diesel, we need to increase the energy density of the fuel. One solution is Liquefied Natural Gas (LNG). The problem with developing the use of LNG in vehicles is not a technological problem, rather it is that there are no Standards to certify or homologate the application of a LNG supply system to the vehicle. Vehicles running on LNG have a close technical similarity to CNG vehicles, the differences are mainly the LNG storage tank, which is a tank that stores LNG at cryo temperatures (-160 ºC) at pressures from 1 to 3 Mpa (10 to 30 Bar) and the vaporizer that converts the gas from liquid phase to gaseous phase. From the vaporizer, the system is just like a CNG system and all of the components could be certified using existing Standards (R110.00 ECE) IDIADA has been working with two partners: IVECO and INDOX Cryoenergy, on applications to vehicles (trucks) running on LNG. We have developed a procedure to register the prototypes and allow them to be used on public roads. The LNG system was designed in order to get the same performance as a CNG system from the point of view of minimum number of components in the system and its function and effect on the safety performance; so similar (where possible) installation prescriptions have been considered. With the experience we have gained, we are now participating in working groups to create a national standard for Spain and an ISO Standard (12614) with the object of making the existence of long range trucks and coaches running on LNG possible. Some issues should be solved, or at least controlled, including limiting prescriptions. This is is the case of the boil-off effect in the cryogenic tank that is responsible for the gas releasing through the safety valve if the vehicle is not running for more than one week. The quantity of gas released is very small and in normal conditions should not be a problem, but in order to be absolutely sure of safety, parking in closed areas will only be possible under certain conditions, for example: if the vehicle is without gas or if the LNG system is connected to a proper system that could manage this gas safely.
KEYWORDS: LNG, GNL, Natural gas standards