Fuel Composition - Blue Bird TC/2000 Owner's Manual

closing the main shutoff on frame and running engine until fuel supply is depleted and pressure is zero.
Contamination of the secondary filter should not occur if a proper maintenance schedule has been followed
at the fill point primary filter. Contamination of the secondary filter also shows that CNG storage cylinders
on the vehicle are contaminated. The owner/operator should insist that fuel from a compressor station should
be clean and dry.
Replacement filter elements are available through the Blue Bird Service Department.

FUEL COMPOSITION

Natural gas composition varies throughout the country, depending on original gas composition and pro-
cessing. Pipeline quality natural gas is composed of several different gases, of which methane typically
accounts for 85 to 99%. Other hydrocarbons present in natural gas include ethane, propane, some butanes,
and trace amounts of other hydrocarbons. Nitrogen, helium, carbon dioxide, and trace amounts of hydrogen
sulfide, water, and odorants are also present. Most natural gas available does not vary significantly in con-
tent; however, significant variations are more likely from small gas utilities. The removal of all carbon diox-
ide, water, hydrogen sulfide, and odorants is required for liquefaction, thus LNG does not contain these
constituents.
The importance of gas composition to users of NGVs is as follows:
Large amounts of non-methane hydrocarbons will enrich the fuel mixture, reduce the octane number,
lead to increased hydrocarbon emissions, and increase the potential for engine knock. Accordingly, engine
parameters such as air/fuel mixture and ignition timing should be adjusted on the basis of the composition of
the local natural gas supply.
REFUELING
CAUTION: Refueling must be conducted in well ventilated areas to prevent accumulation of dangerous
gas levels.
The National Fire Protection Association has recommended guidelines for CNG refueling systems. State
and local regulation regarding NGV refueling may preclude economic feasibility of indoor refueling (such as
in New York City). However, the significance of this issue may diminish if increased experience with fuel
leads to less stringent regulations.
CNG refueling transfers natural gas under pressure and may be set up as either slow-fill or fast-fill. Slow-fill
generally uses overnight refueling and requires less costly refueling station equipment than fast-fill. How-
ever, fast-fill refueling time is only slightly longer than gasoline refueling time. LNG refueling transfers a
cold (-260 o F) liquid under pressure (around 15 psi) and generally takes slightly longer than conventional
refueling because a greater volume of liquid is transferred to compensate for its lower energy content.
The refueling station has a supply connection hose and a coupling which must be properly attached to the
fuel system fill valve. The supply side is regulated for maximum pressure and uses a proper purge valve
when decoupling from the filler. The regulators and relief valves of the fill station must be checked for proper
values and operation.
Fuel enters the bus coupling from the filler connection, travels through a one-way check valve into the
fuel lines and then into any open tanks. Any tank that is open is in communication with any other open tank
through the common fuel lines.
CAUTION: Do not refill with the engine running or any source of ignition or heat nearby. The refueling
station must be in a safe working condition with approved operable relief and vent valves.
NOTE: A ground stud is provided for attachment of the grounding cable at the compressor station. Check
that the tank shutoff valves are open. Any tank with an open valve will be filled, any tank with a closed valve
will not. If the bus has been operating with some tanks closed, it is preferable to fill the empty tanks first and
then fill the remainder. Fill to the desired pressure. Maximum is 3000 psi temperature corrected to 70 degrees
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