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ENGINE
5
A Fuel Selector Switch is provided on the dashboard
to select the fuel desired by the driver
Starting:
Winter:
The engine starts in petrol mode irrespective of the
fuel mode selected when the engine /coolant
temperature is 10deg C and below which typically
occurs during the winter season. The engine
converts to CNG mode automatically when the
engine warms up.
Once warmed up, the engine starts and runs in
CNG, if CNG mode is selected
Other seasons:
The engine starts and runs in CNG, if CNG mode is
selected
Starting time in CNG will be longer than in petrol
(approx 1 sec longer than petrol starting time) due to
the physical characteristics of the fuel.
To start, turn the ignition “ON”, press the clutch pedal
fully and crank. Do not press the accelerator pedal.
Important:
Your car will run automatically in petrol mode for
almost 2 to 3 km after every 60-70 Kms covered in
CNG mode to keep the petrol system & CNG
system in good condition
.
Idle Air Control:
Proper Idling of the engine is ensured irrespective of
the fuel modes - CNG or Petrol - under different
operating conditions with the help of closed loop
control. The ECU controls the IACV to ensure stable
idling.
Engine Load Determination:
CNG Fuelling and Ignition timing requirements of the
engine are dependent on the Engine load. The Load
determination is done using the 'Model Based
Fuelling' (MBF) strategy. The strategy uses the
estimated temperature and pressure at the intake
port together with the engine speed to estimate the
amount of air entering the cylinder at the next
induction stroke. To calculate the airflow as precisely
as possible, a thermal model of the Intake manifold
is used, which is a correction factor applied to the
load equation to determine the correct amount of the
fuel to deliver to the engine. This model also serves
as a backup strategy if either the Throttle Position or
Manifold Absolute Pressure Sensors fails. The
manifold also takes into account of all temperature
variations (E.g.: purging) that will occur during the
running.
Fuelling (CNG):
The CNG in the form of a ‘gas’ is injected into the
Inlet ports by the Gas Injectors. These injectors are
controlled by the ECU for the precise injection
quantities and timings. The amount of the fuel
delivered during each engine cycle is proportional to
duration of the Injector open time. Injector timing
(phasing) is controlled to optimise performance.
The injection is sequential i.e. each injector is
opened relative to its own cylinder timing. Amount of
the ‘fuel’ required (i.e. the Injector pulse time)
depends largely on the engine load and speed.
Further adjustments are to account for the variations
in the operating conditions (CNG temperature &
CNG pressure).
A closed loop fuelling system is used – a further
correction is applied to the open loop pulse time to
maintain a stoichiometric air fuel ratio. The closed
loop system also provides adaptive (‘Learning’)
fuelling to compensate for the component tolerances
and aging. The deceleration fuel cut-off is provided
for fuel economy and improved emission
performance.
Ignition:
The Ignition is controlled electronically by the ECU.
The optimum ignition timing is maintained depending
upon the engine speed and load. Further small
corrections are applied to improve drivability and to
account for the variations in the operating conditions
(e.g. engine temperature, Inlet air temperature). The
ignition timing is also adjusted in conjunction with the
Idle Air Control Valve to control the idle speed of the
Engine.
In order to provide the best torque in both petrol and
CNG modes, the ECU has dedicated ignition timing
maps for check fuel mode which is mapped to
provide optimum torque without knocking.
Throttle Position and Adaptation:
The throttle position potentiometer output may differ
between vehicles and can also change overtime due
to component aging. A corrective term is applied to
compensate for this effect; this is an adaptive
(‘learning’) value that’s updated throughout the
vehicle’s life