Switching from petrol to natural gas, the costs of driving can be lowered by more than 50% if you use your car a lot. Currently (2005) a kg price of approx. 75 cents faces a litre price of approx. 1.20 euros. The reduced tax is guaranteed till 2020. At a natural gas filling station the customer still feels to be in the centre and is lured with vouchers among other things. Natural gas-operated vehicles are environmentally friendly. This is obvious from the fact that oil remains much cleaner if the engine is operated with natural gas, and the spark plugs must be changed less frequently. Because natural gas, in contrast to liquefied petroleum gas, is lighter than air there are no general legal restrictions for underground parking.
You need not fear an explosion. The system features so many safety enhancing components as nearly no other system in the car area. In addition, natural gas is supplied with odour substances. Escaping natural gas would be easy to perceive, suitable measures could be initiated long before forming of an ignitable mixture. The gas tanks (see figure 2) from steel and recently also from fibre composite materials are submitted for an impact check to prepare them against accidents. Only certain upgrades, done afterwards, might be worrisome, because they could threaten rear passengers if the tank is mounted in the boot in case of rear impact. Maybe the biggest disadvantages is the higher vehicle weight, the diminished boot space if the car is adjusted afterwards, and the costs for the adjustment or for the adapted new vehicle which are clearly higher than for liquefied petroleum gas.
Additional disadvantages: at the moment max. 300 km of range with natural gas operation. The performance, the torque and the efficiency with natural gas are different. There are motor control units that make use of the changed ignition behaviour of natural gas (octane rating 120) so well that no difference is perceptible to the petrol fuel operation. In monovalent operation the engine can be adjusted even better to the different fuel. Maybe in combination with the variable compression, the higher octane rating of natural gas will be even better usable, also at bivalent operation. Also the additional tanks must not always devour precious space if the petrol tank is reduced in exchange. Therefore, and also because of the high costs (2500 - 3500 euros) a retrofitting does not always make sense. The complete manufacturer's construction should be favoured.
Natural gas is stored in one or several thick layered containers (see figure 3) under a pressure of approx. 200 bar. If they are mounted directly underneath the vehicle floor, they must be checked every 5 years against relatively high fees. In the pipe there are a manometer to display how full the tank still is, and the connection for the filler neck. The equipment is not compatible to that of liquefied petroleum gas which feature a considerably lower pressure (max. 20 bar). Subsequently, there are the relief valve and another valve which reduces the high pressure depending on the coolant temperature to approx. 8 - 10 bar.
There are vehicles for pure natural gas operation and vehicles in which you can switch between natural gas and petrol (bivalent drive). The latter can dispose of a common control unit or like on top in the figure two separate control units. The natural gas control unit provides via magnetic valves for the injection in the inlet manifolds of the single cylinders depending on the inlet manifold pressure, Lambda tension, throttle flap position and engine speed. The starting takes place mostly with petrol and sometimes directly with natural gas. In case of disturbances in the natural gas system or if the pressure drops below approx. 10 bar it is automatically switched to petrol. Because of the temperature decrease due to the pressure decrease, the natural gas system must be connected to the coolant cycle.
Natural Gas Running Natural Gas Running