Natural gas is a mixture mostly comprising methane; the percentage of which, like the other components, varies from gas field to gas field.
The main characteristics of domestic and imported gas are within a fairly limited tolerance range; the methane (CH4) is present in percentages of 79 – 99%. The minimum percentage of methane required by the Cursor engine, according to specifications, must be > 83%. Other components usually include ethane (C2H6), propane (C3H8), butane (C4H10), nitrogen (N2), carbon dioxide (CO2).
Natural gas is colourless, odourless and is non-toxic.
The injection electronic control systems for methane engines are “self-adaptive” type, meaning that they are capable of automatically modifying the injection parameters when dealing with gasses of different composition.
The gas is stored on-board the vehicle at a pressure of 200 bar inside special cylinders, which are fitted with safety devices. The engine is fuelled via a pressure regulator at 8.5 bar for Cursor 9 Natural Power engines 400 Hp.
Approval of vehicle components:
1. CNG refuelling box (accessible to refuelling crew exclusively from the right side of the vehicle).
2. Safety solenoid valve.
3. Methane cylinders (4×115 L on left side + 4×115 L on right side)
4. Ventilation valve.
5. Pressure regulator.
Benefits of using CNG as engine fuel
• The gaseous state and high anti-knock properties make natural gas a suitable fuel for spark- ignition engines with a high volumetric compression ratio (up to 12:1).
• The high methane number gives natural gas considerable resistance to knocking.
• Given the initial purity of the fuel and the lack of additives (except for odorants), the combustion leads to a limited formation of deposits and an extremely reduced quantity of sulphurous products.
• It is possible that there may be some condensation (extremely limited) inside the pipes and in the combustion chamber (water in oil), the water evaporates immediately due to the heat of the engine.
• The technology offers the following benefits:
– the emissions of particulate, typical of Diesel engines, are eliminated at the source and therefore are absent from the controlled ignition engine;
– it reduces gaseous emissions (unburned hydrocarbons – HC, carbon dioxide – CO and oxides of nitrogen – NOx) through the use of a three-way catalytic converter.
– it does not have emissions of higher hydrocarbons, such as benzene.
– it reduces carbon dioxide emissions by comparison with diesel or gasoline.
– it significantly reduces noise, due to the controlled ignition engine.
Presented by Romano Pisciotti
Motor Parts Industry ( IVECO)
IVECO STRALIS CNG