Antiknock Properties; Energy Conversions; Vehicle Performance And Emissions; Starting Procedure - Blue Bird D3RE 2014 Driver's Handbook Manual

DRIVER'S HANDBOOK

Antiknock Properties

Natural gas has a research octane rating of about 130, making it relatively resistant
to engine knock. The antiknock property is a result of the high ignition temperature,
resistance to auto-ignition, and the relatively low flame speed of natural gas. An-
tiknock properties allow the use of engine compression ratios in the range of 15:1
(compared to 8:1 to 10:1 for gasoline). The low flame speed of natural gas results in
a longer duration of combustion. To compensate for the lower flame speed, ignition
timing is advanced. As with other fuels, knock may occur with advanced ignition
timing, prolonged combustion (i.e., too lean a mixture), and excessively high com-
pression ratios.

Energy Conversions

100-125 cubic feet NG = 1.0 gallon gasoline
114,000 Btu = 1.0 gallon gasoline
136 cubic feet NG = 1.0 gallon diesel
83,700 Btu = 1.0 gallon LNG
1 cubic foot NG = 1,000 Btu

Vehicle Performance And Emissions

NGV performance, fuel economy, and emissions can be significantly altered with ve-
hicle tuning (i.e., ignition timing, air/fuel ratio). Appropriate tuning adjustments can
optimize performance, fuel economy, and emissions. Alternatively, a compromise
tuning may be effected. Tuning optimization for power generally increases emis-
sions. Substantial improvements in performance and emissions can be obtained
using natural gas conversion kits specially designed for a given vehicle make and
model. Further improvements can be achieved with factory-built, dedicated NGVs.

Starting Procedure

Make sure that the main shutoff valve and at least one tank valve are open. The fuel
gauge shows empty if no fuel is available to the mixer. Check the tank and main fuel
shutoff valves if no fuel is indicated on the fuel gauge. (Note that fuel gauge takes
time to register after turning the key.)
Starting procedures are the same as for starting a gasoline engine vehicle. With
the vehicle in neutral, turn the key until the engine catches. Do not press the ac-
celerator. If the engine has trouble starting, depress the accelerator slightly and
release when the engine catches. Pumping the accelerator does not help start the
engine. Engine operation and characteristics should be similar to those of a gasoline
engine.
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