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CNG-NGV Conversion on EFI Vehicles (NGV EFI 101)



Written and Presented by Dr. Xander Thong (MVLK Certified Gas Installer, Malaysia)


 CNG-NGV Conversion on EFI-Type Engine for petrol (gasoline) vehicles. This type of conversion is commonly known as  Closed Loop System CNG-NGV conversion. It primarily involves a CNG-NGV kit, an Air-CNG venturi-mixer, CNG Cylinder, Injector Emulator, Anti-Contaminant Emission System (AES), Step Motor, Timing Advance Processor and accessories.


CNG-NGV Conversion on EFI-type vehicles require more electronic devices as part of the conversion equipment. In the 2nd Generation NGV techology, EFI vehicles are converted with Gas Carburetion method as similar to carburetor conversion (Carb 101). Both Carburetor and EFI vehicle uses an Air-CNG Mixer.




 Picture Source: www.ngv.com.my


AES Mixer Installation






 EFI Installed Mixer

An Air-CNG Mixer is sandwiched between the Airfilter hose and Throttle Body




The CNG gas is pre-mixed with fresh air from the air-filter and introduced into the throttle body of the vehicle. The mixer acts as the carburetor unit, while the petrol (gasoline) supply is discontinued with additional electronic device called an Injector Emulator. The air-CNG must be pre-mixed almost at stoichemetric (17.2) to obtain an efficient air-fuel balance. The Pre-mixed Fuel will enter into the inner parts of the throttle body, while it is constantly controlled by the Throttle Valve (or Butterfly Valve as known to many people).



Picture Source: www.ngv.com.my



 Kings of NGV Vehicle




4WD Vehicles


EFI-Type Vehicles found in Malaysia







CNG-NGV Conversion for EFI Vehicle (EFI 101)


CNG-NGV conversion on EFI-type vehicles can be considered as a modification on the fuel system. The general method is air-fuel carburetion (in 2nd Generation NGV Technology as compared to 3rd Generation), which uses an Air-CNG mixer as the key component. Other components include:

(a) CNG Cylinder (ISO11439 rating), cylinder mounting bracket + high-tension bolts & nuts;

(b) CNG-grade Pipeline, gas venting hoses + accessories;

(c) CNG Solenoid, Manometer (Pressure Gauge), CNG Reducer/Regulator kit + mounting brackets;

(d) NGV Refilling Valve;

(e) Master Shut-off Valve at cylinder (PRD) and refilling valve

(f) EFI Switch-over (or Fuel Selector switch);

(g) Petrol Injector Emulator;  

(h) Timing Advance Processor (for Gas Spark Ignition Timing); and

(h) Anti-contaminant Emission System (AES) and Step Motor Gas Controller;

(i) Signal from Oxygen (Lambda) Sensor and Throttle Position Sensor (TPS).






Picture Source: www.landirenzo.com  


EFI AES CNG Conversion






 Air - CNG Mixer (Key Component)


Air-CNG Mixers is the most important component in the CNG-NGV Conversion. Each vehicle model uses a different Mixer design and specification. A mixer is engineered and manufactured to work with the dynamics of its intended carburetor unit. Without or with poorly designed/manufactured mixer, the NGV vehicle will experience many mechanical and performance problems.

Kindly ensure that you use only the Genuine mixer  designed for your vehicle engine type before embarking on CNG-NGV conversion. All mixers are different, and do NOT believe that  one mixer fits all vehicle models, as claimed by many unethical NGV Installers worldwide.   





Picture Source: www.ngv.com.my


CNG Mixers

(there are over 200 types of mixer availabble)




A good Air-CNG Mixer is commonly constructed with composite metal material which is capable of resisting extreme heat and engine temperatures. There are also technical specifications of 'Venturi' measurement for good partial-vacuum creation (in turn used by the CNG Reducer Stage 3 to detect the volume of gas to release/reduce into the engine). Basic: Venturi Principle - http://en.wikipedia.org/wiki/Venturi



Picture Source: www.ngv.com.my

CNG Mixer Demo

 CNG\LPG Mixer for Most Japanese Vehicles





All good mixers have special measurements to areas of venturi inlet, cross-section and outlet. The venturi inlet is the area that constrict the airflow from the airfliter. The approximate degree of the venturi inlet angle is about 40 degrees and tooled to a smooth rounded surface (to avoid friction with the incoming air). As per the cross-section, the hole in the middle of the mixer. It has a special diameter corresponding to the vehicle engine displacement (or cc). The bigger the cc is, the wider will be the cross-section to allow more air to flow through to match the larger-sized cylinders. On the propeller, it functions as a hurricane device to create a swirling vortex between the air and the CNG gas for better mixing. Some vehicle needs the propeller for better carburetion, while others don't. It depends purely on the engine's throttle body.The venturi outlet is the area where a partial vacuum is created. The partial vacuum will suck out the CNG gas from the pipeline connecting the CNG reducer/regulator. As the gas is sucked out by the partial vacuum, a diaphragm in the regulator will move corresponding to the volume of gas sucked out (technically, the pressure drop in the connecting pipeline). When this diaphragm moves, a sensor is activated to release more gas to equalise the pressure in the connecting pipeline. Thus, you will know now that our NGV Regulator is a sensor-activated diaphragm device to increase/decrease CNG gas flow as a result to the volume of partial vacuum created by air rushing  into the engine. Dirty airfilter can reduce the air rush .  


With good quality Air-CNG Mixer, You can expect:
(a) A very stable engine idle.
(b) Easy engine tuning.
(c) Good pick-up and very responsive engine (when pressing the pedal).
(d) Good Gas consumption, but not better than having TAP.
(e) Better braking performance
(f)  Engine will not stall/cut-out upon braking (unless tappet adjustment is off).







CNG Cylinder (ISO 11439 Rating)


The Cylinder is used to store compressed natural gas (CNG)at a working pressure of 200-250 bar. It is fitted with a shut-off valve in case of gas leakage. The cylinders have a valve and Pressure Relieve Device (PRD) that must be installed very tightly. For this purpose, the cylinder is placed on a specially prepared bracket-clamp that will secure the tank to prevent it from turning when the valve is being tighten during installation. Before installing the valve in the cylinder thread, 30 rounds of Teflon tape (or any gas sealing tape) must be applied for better sealing. The valve must be tightened with no greater force than 25 kgm. The cylinder(s) should be placed in the same direction as the car axle.



 Picture Source: www.ngvcommunity.com  


 EFI Cylinder 1

2 x 40 Water Liter CNG Cylinder on a Proton Waja (1,600cc EFI) - Malaysia



 EFI Cylinder 2


2 x 40 Water Liter CNG Cylinder on a Proton Waja (1,600cc EFI) - Malaysia




The Manual Safety Valve must be easily accessible, so that it can be closed without problems in case of a leak. On the same side on which the cylinder valve is placed, one hole has to be made in the lower part of the trunk, to place the ventilation nozzles. This hole will allow ventilation of any gas leakage from the cylinder valves. To achieve this, before connecting the high-pressure piping to the valve, a ventilation bag must be placed on it and on the ventilation tube on the high-pressure piping.


Picture Source: www.ngv.com.my


Pajero Cylinder Safety

 Venting Hoses installed on a Mitsubishi Pajero V32 - Malaysia







CNG-NGV Reducer\ Pressure Regulator


CNG-NGV Reducer (or Pressure Regulator) is an electronic control device that reduces CNG pressure from 200 bar to 3-5 bars and producing a regular flow of gas fuel for the engine's needs. It is equipped with three CNG reduction stages that allow stability at both high and low pressures and a high-pressure solenoid valve upstream from the first stage. The absorption of heat, taken from parts of the regulator, heated with a tap-in engine coolant, prevents the sensor-diaphragm from freezing up during the fall in pressure phase. The flow of gas necessary for engine idling is obtained throught the main gas pipe thanks to the vacuum generated by the Mixer. It includes an electronic starting device with built-in safety system that trips and shuts off the gas solenoid valves if the engine is switched off or even when it stalls. 


Picture Source: www.landirenzo.com


CNG Regulator

 Landi Renzo (Italy) Regulator comprise of 100, 140, 180 210, 250HP





Picture Source: www.zavoli.com 


 CNG Regulator - Zavoli

 Zavoli (Italy) Regulator comprise of 100, 140, 180, 210HP



Most regulator kits have built-in CNG solenoid valve, controling CNG to flow from the regulator into the Air - CNG Mixer. (Or, it shuts off the CNG when the engine is not running or when, in the case of a bi-fuel vehicle, gasoline is selected).







Manometer (Pressure Gauge) And Bi-Fuel Switch-Over


The selector Switch is fitted at the dashboard, enabling the driver to choose either the CNG mode or the petrol mode of operation. The electronics built into this unit also ensures safety by switching off the gas solenoid whenever the engine is switched off. It also indicates the quantity of CNG available in the cylinder.


Picture Source: www.ngv.com.my


CNG Manometer & Switchover


The wires that connect the switch to the different parts of the system must pass from the dashboard to the engine bay and should be secured by plastic ties. All connections must be made with the terminals supplied for that purpose. For EFI vehicles, the Switchover is programmable for automatic petrol (gasoline) change-over to CNG-NGV at pre-set parameters. Commonly, an EFI NGV vehicle will start-up with petrol (gasoline) and drive on for a change-over to CNG-NGV when pre-set parameters are met, such as Deceleration from 2,000rpm onwards or CNG reducer temperature achieving 49oC. Thus, EFI vehicle has automatic change over from petrol (gasoline) to CNG-NGV with a programmable Switchover.


Picture Source: www.digicarsystem.com

EFI Switchover







CNG - NGV Refilling Valve


Natural gas is compressed and enters the vehicle through the CNG-NGV Refilling Valve, directly into the CNG cylinder. The refilling valve must be mounted with a specially designed metal bracket, which is to be affixed to the vehicle body with bolts & nuts. The bracket of the filling valve has a hole; a part of the valve passes through it and the end is fixed with a nut. Both the bracket and the valve must be rigidly mounted to withstand the pressure of the hose nozzle every time gas is loaded. This component must not be installed near the car battery, to avoid the possibility of a spark while loading; a spark combined with gas can cause an accident. It is also advisable to place it near the regulator, so as to be able to control the filling pressure with the system manometer.


Picture Source: www.ngv.com.my

OMB Refilling Charge

 Refilling Valve and Refilling Charger (NGV-1 Standard)




A loop or Pig-Tails must be made between refilling valve and CNG reducer\regulator every time there is a change in direction of the pipe, or only one if the pipe maintains one direction. It is very important that this section be as short as possible, to avoid passing over other equipment in the engine bay.

Picture Source: www.ngv.com.my


Pig-tail Iswara 

 Pig-Tail at 90o Angles on Pipeline, Mixer, Petrol Solenoid, Voltage Stabilizer, Power Screw







Petrol (Gasoline) Injector Emulator


Injector Emulator are devices that make it possible to interrupt the petrol (gasoline) flow during CNG-NGV operation and at the same time simulate the correct operation of injectors or of the petrol (gasoline) supply system by means of heating elements or inductors (as injector sensor) that are duly calculated according to the ECU on the vehicle as 'Function' or 'NO Check Engine Alert', where as petrol supply has been discontinued.


Picture Source: www.digicarsystem.com


Injector Emulator

 Injector Emulators based on vehicle's Injector Specification


Document Download Icon  Advertorial:  Download e-brochure on Digicar Products with Installation & Wiring Diagram







Anti-Contaminant Emission System (AES) And Step Motor 


It is a close loop system. The natural gas flow, is regulated with a valve driven by a stepper motor. The valve position depends on the oxygen concentration in the exhaust gases. This concentration is measured by a sensor called “Lambda Sensor” or “Oxygen Sensor”, which is located in the exhaust pipe.The lambda sensor signal is analyzed in the Control Unit, which, taking into account the engine load, drives the valve to the optimum position.


Picture Source: www.galileoar.com 


AES Flow Chart

Signal Feedback And Regulaton of CNG Into the Engine



The Anticontaminating System's target is to maintain the fuel mixture in its optimum point (Stoichiometric Mixture) . In this way the combustion chamber temperature will be maintained between safety limits.


Picture Source: www.ngv.com.my

AES Step Motor

AES Unit, Step Motor, Handheld Programmer




Picture Source: www.digicarsystem.com

Heldhand Programmer

Hand-Held Manual Programmer (for Both Installer or NGV User) 




Stoichiometric Mixture

Molecules of fuel react with air, exactly with the oxygen contained in it. When every molecule of fuel is combined with every molecule of oxygen, that means that there is no free fuel or air, the mixture is called “Stoichiometric”. When we are working with CNG, the air – fuel ratio is 17.2 parts of air for every part of natural gas. For petrol combustion the ratio is 14.7:1.


Rich Mixture

When the CNG concentration is major than the ideal one, it will exist free fuel in the exhaust gases. When this occurs the mixture is called “Rich”.


Lean Mixture

When the fuel concentration in the air – fuel mixture is minor than the stoichiometric one, the mixture is called “Lean”. This is a very dangerous situation for the engine. On one hand, we have low fuel consumption, but on the other hand it raises the combustion temperature. Moreover, the engine will produce a large concentration of nitrogen oxide. To sum up, the temperature could reach dangerous values that could damage the engine.



Lambda Sensor

Air concentration in exhaust gases is measured by the lambda sensor. This device sends to the AES an analogical signal which vary between 0 – 1 Volts (generally). For lean mixtures, voltage range will be between 0 to 0.5 volts and rich mixtures will be between 0.5 to 1 Volts. These sensors are located in the exhaust pipe before the catalytic converter. Any fuel injection systems have more than one sensor, one after the catalytic converter and another one after it. The first one senses mixture condition.







Anti-Contaminant Emission System (AES) Interface Software with PC Programming 


For CNG-NGV Installers, AES devices can be configured manually through an interface software. This configuration is necessary at the initial stage of CNG-NGV conversion process in any EFI vehicle. The software provide the facilities to set in the correct (or adjustment) working parameters for the AES and Step Motor. Without setting up the parameter limits, the AES and Step Motor may not function properly on the intended EFI vehicle. It is a necessity as dictated by engineering variances in each vehicle make, model, engine type and oxygen sensor. 




 Picture Source: www.ngv.com.my


 Digicar LC 10 Interface Software



After this software programming has been completed, a handheld manual programmer can be used to adjust the AES and Step Motor independently.  








Timing Advance Processor (TAP) or Advance Corrector


Timing Advance Processor can be used on all electronic ignition composed by high tension rotary distributor and a power amplifier. The timing advance processor adjusts the ignition timing, when the engine is running on gas and resets the original advance (timing) when the engine operates with petrol. The timing advance processor improves performances and consumption on CNG-NGV operations.



Picture Source: www.aeb.it







 Picture Source: www.landirenzo.com


  EFI Tap


Timing Advance Processor (TAP) for EFI Vehicles
















Written and Presented by Dr. Xander Thong, MLVK Certified Gas Installer (Malaysia)

(If you have noticed any error or inaccuracy, kindly email and notify to drxander@ngvcommunity.com)



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