Commissioning
Unless otherwise requested by the operator, the commissioning process normally
involves adjusting the Gaseous Fuel System controls to allow for the maximum
possible gas ratio (minimum possible diesel fuel consumption) while
simultaneously maintaining the engine in a safe operating range.
The
commissioning process can generally be divided into three distinct phases
involving:
- Testing of the engine to confirm baseline performance,
- Reduction
of engine h.p. using either the Aneroid Control Valve or the Diesel Control
Valve (no gas)
- Recovery of engine h.p. to the baseline level established
in step 1 above using natural gas.
Since fuel consumption is typically linear compared to engine load, it is
possible to estimate the gas-diesel ratio by comparing peak engine h.p. values
in steps 2 and 3 above (when using a chassis dynamometer).
For example, an
engine which makes 250 h.p (at the wheels) is de-rated to a maximum of 75 h.p.
(step 2).
Using gas, the engine h.p. is set back to 250 wheel h.p. in Gaseous
Fuel mode (step 3).
In this case, the approximate gas ratio at peak engine power
is 70% (with 30% diesel pilot), since 70% of the engine h.p. was “recovered”
using natural gas (250 h.p. x 0.30% = 75 h.p.).
In most cases, maximum gas ratio
will be limited by one or more of the following factors:
- Engine Exhaust Gas Temperature (EGT)
- Engine Knock
- Engine Stability
- Engine Durability
Commissioning MethodsPreferably, engines should be commissioned in Gaseous Fuel mode using a chassis dynamometer. This method has several benefits including the ability to more
precisely set the gas-diesel mixture as well as the ability to fully test the
engine across the load / speed range.
In the event that a chassis dynamometer is
not available, the engine may be commissioned "on-road" if necessary.
On-road commissioning generally takes longer to complete (compared to chassis
dynamometer method) and normally requires that the vehicle be placed in service
to confirm operating gas-diesel ratio and engine characteristics, since it is
typically difficult to simulate loaded conditions.
Commissioning Process - Chassis Dynamometer
The commissioning process requires that the vehicle be operated at high speeds
and power loadings on the chassis dynamometer.
In order to monitor engine EGT during the commissioning process, the use
of a hand-held, infrared temperature monitor is recommended (range >1200 F/ 650
C). EGT should be monitored at the turbine inlet (turbocharged engines) as well
as at each cylinder exhaust port to confirm proper temperature balance between
cylinders. It is also possible to utilize the ECS EGT thermocouple to monitor
engine EGT using a hand-held temperature monitor (compatible with K-type
thermocouples).
The commissioning process will require extended operation of the vehicle
on the chassis dynamometer (dyno). Adequate cooling of the engine and vehicle
must be maintained (using a fan or other means) to prevent overheating of the
engine and/or drive train.
Notes Regarding On-Road Commissioning
In the event that a chassis dynamometer is not available, the engine may be
commissioned in Gaseous Fuel mode.
In order to replicate this process, it will be necessary to devise
a method to consistently load the engine / vehicle.
As an
example, engine performance (power) may be inferred by comparing the relative
time it takes the vehicle to cover a particular straight distance, or
alternately, the time it takes to climb a particular hill or grade. Note that
unlike the chassis dynamometer method, the on-road method does not provide
empirical data relative to engine h.p. or torque therefore making an accurate
estimate of gas-diesel ratio somewhat more difficult.
In addition, it is often
more difficult to monitor other engine parameters. In most cases, a vehicle commissioned on-road will need to be placed in service
(or otherwise operated for a significant time/distance) in order to confirm
actual operating gas-diesel ratio and general performance in Gaseous Fuel mode.