The gas train includes a Gas Pressure Transducer (GPT)
for monitoring CNG fuel pressure. The GPT is installed upstream of the HPR
regulator using the supplied adaptor fittings. Depending on GFS kit model, the
GPT may be rated for 2,400, 3,000 or 3,600 psi operation (165, 206 or 247 bar).
The Air-Gas Mixer (AGM) blends engine intake-air with an appropriate quantity of
natural gas as required for combustion. The AGM is installed upstream of the
turbo-compressor inlet and downstream of the engine air cleaner housing. The
patented GFS Air-Gas Mixer is a "fixed venturi" design and therefore does not have
a moveable air-throttle.
Air entering the AGM is diverted around a gas diffuser section, causing a
turbulent, low pressure area to form. This low pressure area draws natural gas
from the diffuser section gas reservoir through a radial pattern of precision
machined gas outlet orifices.
Gas is introduced into the turbulent airflow area
immediately downstream of the gas diffuser section, allowing for a high degree
of mixing action of the two media. The Gaseous Fuel System Air-Gas Mixer
provides for a high degree of air-gas blending with a minimum of airflow
The AGM design includes an integral Gas Power Valve (GPV). The GPV is a
proprietary flow metering device that allows for precise adjustment of gas flow
to the engine. The GPV utilizes a needle and seat type flow adjustment,
comprised of an adjustable threaded gas screw and seat.
Once set, the gas screw
position sets a fixed and limiting orifice inside the power valve body, thereby
controlling the maximum flow of gas available across the engine load range. By
using the adjustable gas screw, the operator is able to set the desired
The CAD designed AGM is constructed of aerospace quality materials that have
been CNC machined and then assembled using a state-of-art welding process.
The AGM is mil-spec anodized for surface hardness and corrosion protection. The
GFS Air-Gas Mixer comes standard in 4", 5", and 6" O.D. (101.6, 127, 154.4 mm
Electronic Control System
The Gaseous Fuel System is supplied with an Electronic Control System (ECS) that
monitors engine exhaust gas temperature and monitors/displays CNG supply
pressure and level.
Based on sensor inputs and factory-set limits, the ECS will
activate or deactivate gaseous fuel mode as required. Depending on the model of
Gaseous Fuel System, the ECS will be configured for either 2,400 3,000 or 3,600
psi (165, 206 or 247 bar) operating pressure.
The controller sub-kit is supplied
with the necessary sensors, displays and wiring harnesses. The ECS monitors
engine exhaust gas temperature (EGT) using a K-type thermocouple and CNG supply
pressure with a pressure transducer.
The ECS is provided with indicator lights
that provide a quick visual status of the Gaseous Fuel System. If a fault is
detected by the control system, Gaseous Fuel operation is suspended and the
engine is reverted to 100% diesel operation.
Factory programmed setpoints include high engine EGT and low pressure CNG
In the event engine EGT exceeds a value of approximately 1200 deg. F
(650 deg. C), the ECS will automatically revert the engine to 100% diesel
operation and illuminate the amber EGT fault lamp.
In the event CNG supply
pressure drops below approximately 250 psi (1724 kPa), the ECS will
automatically revert the engine back to 100% diesel operation and illuminate a
Both high EGT and low CNG conditions result in a latching fault
condition - the ECS must be reset to clear the fault condition by removing the
DC power supply (typically achieved by cycling the vehicle's key from "run" to
"off" and back to "run").
Diesel Fuel Control
In order to allow substitution of natural gas for diesel fuel, it is necessary
to physically limit the amount of diesel fuel available to the engine injection
system. Depending on engine fuel system configuration, the Gaseous Fuel System
will include one of the following devices:
- Aneroid Control Valve
For engine fuel systems that reference MAP (turbo boost
pressure) using an aneroid, the Gaseous Fuel System utilizes an "Aneroid Control
The ACV is a three-way, 12 volt, DC-powered valve that is
installed between the engine airintake manifold and the air-inlet
port on the OEM fuel aneroid (or pressure transducer in some cases).
When activated by the ECS, the ACV diverts the turbo boost "signal" (air pressure)
such that the aneroid controller maintains the diesel rack in a retarded
position. This has the effect of reducing engine HP by up to 80% and allowing
for the substitution of natural gas for diesel fuel.
When de-activated by the ECS, the ACV allows the normal turbo boost signal to reach the fuel aneroid,
thereby restoring full engine power for 100% diesel mode.
- Diesel Control Valve
For engine fuel systems that do not employ an aneroid fuel
controller, the Gaseous Fuel System utilizes a Diesel Control Valve (DCV).
The DCV is a three-way, 12 volt, DC-powered, adjustable flow control valve. For
engines equipped with in-line injection pumps, the DCV is installed immediately
upstream of the injection pump fuel inlet.
For engines equipped with fuel rails (such as the
Cummins PT system), the DCV is installed after the pressure pump and before the
inlet to fuel rail.
When activated by the ECS, the DCV decreases the flow of
fuel to the injection pump or fuel rail and decreases engine HP by up to 80%
allowing for the substitution of natural gas for diesel fuel.
by the ECS, the DCV allows for unrestricted fuel flow, thereby restoring full
engine power for 100% diesel mode.