Vehicle CNG Conversion system
Introduction: As we have seen the need for CNG in cars are increasing day by day and more
people are adopting CNG Kits as their option for a Better, Cleaner tomorrow, knowing the fact
that it’s economical for pocket and engine friendly also.
Types: There are mainly 3 kinds of kits available in Bangladeshi Market Conventional, Lamda
Control & multipoint Sequential Injection system. A lot of CNG Kit users and CNG enthusiasts
are un-aware / confused about the three technologies, but the difference is quite simple.
Conventional System: The CNG Reducer supplies the CNG Gas to the Engine through a
locally made Air Gas Mixture which is not supplied by the CNG Kit Manufacturer; it is then fitted
on the Air Intake (Inlet Manifold) of the Engine. The CNG Gas and Air mixture is sucked by the
Engine which travels through the manifold and reaches inside the engine, according to its firing
As there is no computer control over the flow of CNG gas into car’s engine in a conventional
CNG Kit, an even flow of CNG gas mixture now enters into the combustion chamber and burns
with the help of the Sparks generated by the Spark plugs fitted in the Cylinder Head. If the Plugs
are week then the car can backfire, resulting in a mild explosion within the engine
compartment which is released through the Air Cleaner of the car. This can often result in
blowing off the Air Cleaner assembly of the car. That is why many cars are found with busted
Air Cleaner assy. Another drawback is a compromise of the Engine Power (roughly 10-30%), and
loss of Engine Life due to poor pick up and A/C load.
Lambda Controlled System (LCS): The next improvement in Engine Technologies (BS-III)
little improvement in the CNG Kit technology was achieved with the introduction of Lambda
Controlled System (LCS) or Close loop System & Timing Advancers (TA). A little control of the Gas flow
and poor pick up can be made up with this LCS and TA that are connected with the MAP Sensor, TPS &
Oxygen Sensor (Lambda sensor) fitted in the Engine & Exhaust Manifold (Silencer) of the Car.
Due to the slight improvement in car’s pick-up with CNG Kits fitted with LCS and TA; more users
started to switch to CNG from petrol and the use of A/C on CNG was more effective without
compromising performance and engine’s life.
Multipoint Sequential Injection System or 5th Generation): With the further
advancements in technology and need for better performance from CNG Kits users, Sequential
CNG Kits were introduced to match the performance of EFI or MPFI car by delivering computer
controlled CNG gas injection through nozzles (similar to injectors in Petrol cars) which is
matched to the engine’s original computer for better optimization, increased performance and
power & even better fuel efficiency.
The Difference between a Sequential CNG Kit & Conventional CNG Kits is as
same that of a Petrol Carburetor Car and MPFI Car. In MPFI cars the delivery and quantity of
fuel is controlled by the Petrol Injectors installed in the Cylinder Head Assembly. The Injectors
are connected with the Electronic Control Module (ECM) of the Car which takes signals from
other sensors fitted and helps in improving the pick and mileage of the cars and helps in
reduction of pollutants levels also.
A Sequential CNG Kit works the same way. It has a separate CNG gas ECM and multiple CNG
Gas Injectors to control the flow and quantity of the CNG gas. These are installed just next to
the petrol injectors on the engine cylinder head. CNG gas is pumped inside the engine’s
combustion chamber which results in better fuel combustion resulting in better pickup,
increased mileage, low engine load and no dust entry into the engine when compared to air-gas
mixture installed in a conventional CNG Kit system. No modifications are required in the air
intake system when using a Sequential CNG Kit system than compared to a Conventional CNG
The size of the CNG reducer fitted is smaller than conventional CNG kit and supplies CNG
directly to the CNG Injector rail which takes lesser engine space. The CNG Gas ECM is connected
with the Engine ECM though specially Designed Waterproof Wiring which send the signals to
the CNG Gas Injectors for gas injection.
The ECM receives signals from the MAP sensor fitted in the Car for proper quantity of the Gas
to be released to the Injectors. The quantity of the CNG Gas is also monitored by the Vacuum
Pipes installed. If there is any leakage in the Vacuum system the Gas Supply to the Engine is cut
and it is automatically shifted to Petrol Mode with a buzzer sound installed in the Fuel Change
Reimbursement of Sequential System: The system has a customized software
design, which allows selection of Fuel change, Time, Temperature and Changeover RPM also. It
comes with a very compact sized fuel selection switch with built in buzzer alarm which can be
fitted easily anywhere. If the CNG GAS goes off while driving, the car automatically comes on
Petrol with a buzzer sound. The user cannot judge the difference between the performance in
Petrol / CNG and is useful for cars with Complex Engine Technologies or latest Engine
The fully automatic and self-calibrated GAS ECM does not require tune ups on a regular basis
which save maintenance costs. Even in case of problems the repairing is done through
electronically using the software which automatically detects and fixes any faults in the system
and takes much lesser time than manual calibration. Electronic maintenance reduces chances
of human error and save a lot of time. Even when you take the car for regular service or
maintenance, there is no need for the setting does not changes.
Engr. Mohammad Imam Hossain Rubel
Navana CNG Ltd.