Description and Operation
The properties of null (liquefied petroleum gas)
- is described in the DIN EN 589 standard
- depending on the season and the country, null is blended with approximately 10 to 60% butane (C4H10). The proportion of butane rises thereby with increasing ambient temperature in order to reduce the pressure increase in the gas tank.
- has a knock resistance of approx. 103 to 111 null (research octane number)
- delivers approx. 67% of the energy content of petrol
- compared to petrol-operated vehicles, emits about 15% less null (carbon dioxide), about 80% less null (oxides of nitrogen), about 80% less null (carbon monoxide) and about 60% less null (hydrocarbon)
- is practically free of sulfur and contains no carcinogenic compounds such as benzene
- causes an average increase in consumption of 5 to 25% compared to petrol This increase in consumption results from the lower density, which can only partially be compensated for by the higher calorific value
- burns more slowly than petrol, because of which the gas control module must address the engine management accordingly
- is under pressure (approx. 20 bar in a full gas tank) and stored in the liquid state in the gas tank.
Fuel Tank and Lines
The fuel system for petrol operation and the gas system for null operation are two self-contained systems which are totally independent of each other.
Gas tank filler neck and adapter
The gas tank filler necks may differ from one country to another. As a result, different gas tank filler neck adapters are available. The gas tank filler neck contains a non-return valve. The non-return valve comprises a spring loaded ball which is forced against a plastic seal.
Adapter, gas tank filler neck
The gas tank filler neck must not be dismantled and must be replaced as a complete unit if it is damaged. The inner hexagon is provided as counterhold for this.
Ring-shaped gas tank and gas valve unit
Because liquid gas requires a low volume, the gas tank for null can be made very compact. The ring-shaped gas tank is the preferred layout and often replaces the spare wheel. If there is no spare wheel well, the gas tank is installed under the luggage compartment floor panel.
The gas valve unit controls the gas supply and gas shut-off. The gas valve unit non-return valve is integrated in the gas valve unit and must not be dismantled. The gas pressure release valve, the rear gas valve unit and the gas fill level sensor and display unit can be replaced individually.
The gas fill level limiting valve is part of the gas valve unit. The limiting valve ensures that the gas tank can only be filled to a maximum of 80%. This ensures that enough space remains for the temperature-related expansion of the null.
Another part of the gas valve unit is the gas pressure release valve. It limits the pressure in the gas tank to a maximum of 28 bar. Because the gas tank can only be filled to 80%, the valve is a safety precaution which is usually not called upon. If the valve does open, then gas will flow through the gas tank vent into the environment.
Valve, gas tank
The gas tank valve on the gas valve unit closes the gas tank outlet so that no gas can flow out of the gas tank. If, for example, the rear gas valve unit needs to be replaced, this can be done after closing the valve while the gas tank is full.
The gas tank must be empty before the gas tank valve can be removed.
Gas shut-off valve, rear
The rear gas shut-off valve opens or closes the gas supply to the front gas shut-off valve.
Gas lines and gas hoses
On the high-pressure side, the null is passed through special high-pressure gas lines. On the low-pressure side, the null is passed through special low-pressure gas hoses. The gas hoses must not be repaired. If a hose is damaged it must be replaced with a new hose.
Front gas shut-off valve and high-pressure gas filter
The front gas shut-off valve opens or closes the gas supply to the gas vaporizer. It contains the high-pressure gas filter. The high-pressure gas filter is a coarse filter. It is changed during every service.
The gas vaporizer ensures that the vehicle-dependent gas pressure ("Deltap") in the gas distributor constantly stays at about the pressure in the intake manifold. For this purpose, the gas vaporizer is connected to the intake manifold by a vacuum hose. When evaporation occurs, heat is drawn from the surroundings. The gas vaporizer is pre-heated by the engine coolant to prevent it from icing up.
The gas vaporizer must not be dismantled and must be replaced as a complete unit if it is damaged.
Low-pressure gas filter
The filter element of the low-pressure gas filter can be replaced with a new filter element after dismantling. The low-pressure gas filter is a fine filter. It is changed during every service.
Repair and maintenance instructions
NOTE: Only qualified mechanics who are familiar with the legal requirements are permitted to work on gas systems. Additional health and safety precautions can be found in the relevant subgroup in section 100-00.
NOTE: The overpressure must be released before starting any work on the LPG/CNG system. After the work is finished, a leak test of the complete gas system must always be performed.
NOTE: For repairs requiring an empty gas fuel tank advise the customer to deliver the vehicle with an empty gas fuel tank.
NOTE: The overpressure between the gas valve unit and the gas filler neck remains after the gas pressure in the rest of the system has been released.
NOTE: Further information on releasing the overpressure and the leak test can be found in the relevant subgroups in section 310-00.
General:The vehicle must never be operated with an empty petrol tank, as this would result in damage to the fuel pump for petrol operation.
General: Any excessive heating must always be avoided during any work. Temperatures must never exceed 70°C and the gas tank must be no more than 50% full at this temperature.
General: All work carried out must be recorded in the supplement to the instruction manual for null vehicles.
Gas filter When the filter element of the high-pressure gas filter or the low-pressure gas filter is installed, pay attention to the direction of flow. This is shown by an arrow.
Gas tank: Make sure that the paint on the gas tank is undamaged. If the paint on the gas tank is damaged, the damaged area must be sanded to the metal surface, primed and painted. Position the damping mats so that direct contact with other components is prevented.
Gas tank: Make sure that the seal between the the gas tank and the vehicle interior is leakproof and that the gas tank vent is not blocked.
Gas vaporizer: At each maintenance interval, the adjustment of the gas vaporizer must be checked and, if necessary, corrected. The pressure difference ("Deltap") at the gas vaporizer can be adjusted via a 4 mm Allen key. The adjustment is performed with the aid of the Sequent Plug&Drive autogas (LPG) / natural gas (CNG) diagnostic and programming software.
Gas level sensor and display unit:
Depending on the installed gas control module, the basic setting is checked and if necessary adapted with the aid of the Sequent Plug&Drive autogas (LPG)/natural gas (CNG) diagnostic and programming software after the gas level sensor and display unit are replaced.
The adjustment of the gas fill level display has no effect on the engine management.
The settings for the null (light emitting diode) of the gas fill level display can also be adjusted or reset to the standard values if necessary (depending on the installed gas control module). If a more exact adjustment is required, the settings can be regulated as follows:
NOTE: This procedure requires the gas fuel tank to be empty.
Adjustment of the gas fill levels
Switch to change between % and mV
Input field for empty gas tank
Input field for full gas tank
- Switch the display to "mV".
- Enter the voltage for an empty gas tank.
- Enter the voltages read for the nulls.
- Enter the voltage for a full gas tank.
- When you leave the application, the changes will be saved in a file and transferred to the gas control module.
The gas fill quantities for the particular fill levels can be adjusted as necessary to suit customer requirements.