The
GTI Bi-Fuel System provides gas to the engine using a technique known
as fumigation. In a process similar to that utilized by carburetors
found in spark engine applications, the system supplies gas to the
engine using the original air intake system. In the typical configuration,
the gas is introduced at a location upstream of the turbocharger and
downstream of the engine air cleaner. The gas is introduced at approximately
atmospheric pressure using a proprietary air-fuel mixing device that
allows for a high level of fuel atomization with the smallest possible
air restriction.
After exiting the mixer,
the fuel-air charge is compressed in the turbo and then distributed
to each cylinder by the engine air-intake manifold. The intake valves
deliver the mixture to individual cylinders at the proper moment according
to the normal valve timing of the engine. Upon entering the combustion
chamber, the air-gas mix is compressed during the compression stroke
and ignited when the diesel injector is activated.
Because a majority of
the fuel and air is already pre-mixed prior to activation of the injector,
the combustion differs slightly from the normal "stratified charge"
process of the diesel engine. During bi-fuel operation, the combustion
is slightly accelerated and the pressure rise in the cylinder is slightly
"steeper" than normal diesel combustion.
Peak cylinder pressures
reached during bi-fuel operation, however, are within normal limits.
Although natural gas has a lower energy density than diesel fuel,
the lean-burn/excess air operation of the diesel engine com-bined
with the compression provided by the turbocharger, allow the system
to supply adequate quantities of natural gas to the combustion chamber,
therefore assuring that the equivalent power can be realized.
All OEM engine specifications
for injection timing, valve timing, compression ratio, etc., remain
unchanged after installation of the Bi-Fuel System, and no engine
modifications are required.
