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CNG-NGV Conversion on Carburetor Vehicle (NGV Carb 101)



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






In CNG-NGV Conversion, carburetor-type vehicles are the most easiest to be converted. Since these vehicles operate on air-fuel carburetion method, CNG-NGV uses a similar approach with the employment of an additional Air-CNG mixer (termed as Mixer) to be installed.



Carburetor Mixer Interaction

A - Air\CNG Mixer Carburetion     B - Air/Petrol Carburetion




The CNG gas is pre-mixed with fresh air from the air-filter and introduced into the carburetor unit of the vehicle. The mixer acts as th carburetor unit, while the petrol (gasoline) carburetor is de-activated by a petrol soleniod unit (by disallowing petrol\gasoline from entering the fuel chamber). 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 carburetor, while it is constantly controlled by the Throttle Valve (or Butterfly Valve as known to many people).




Picture Source: www.ngv.com.my

Carburetor Cars

Carburetor-Type Vehicles found in Malaysia






CNG-NGV Conversion for Carburetor Vehicle (Carb 101)


CNG-NGV conversion on carburetor-type vehicle can be considered as a modification on the fuel system. The general method is air-fuel carburetion, 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) Petrol (Gasoline) Solenoid for carburetor vehicle only;

(e) NGV Refilling Valve;

(e) Carburetor Switch-over (or Fuel Selector switch);

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

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






Picture Source: www.landirenzo.com  

Carburetor CNG System Conversion






 Air - CNG Mixer (Key Component)


An air-CNG Mixer is the most important component in the CNG-NGV Conversion. Each vehicle model has 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 a 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's engine type before embarking on CNG-NGV conversion. All mixers are different, and do NOT believe the talk that one mixer fits all vehicle engine types, 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 to resist extreme heat and engine temperature. There are also technical specification 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. As sample, it is the area with the darkened metal. The approximate degree of the venturi inlet angle is about 40 degree and tooled to a smooth rounded surface (to avoid friction with the incoming air). As per the cross-section, the area is the propeller-looking darkened metal. 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 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 diagphram 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 tightened 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 should be placed in the same direction as the car axle.



 Picture Source: www.ngv.com.my


Iswara NGV Cylinder

A 55 Water Liter CNG Cylinder on a Proton Iswara (1,500cc Carb) - Malaysia




Kancil NGV Cylinder

A 62 Water Liter CNG Cylinder on a compact-car Perodua kancil (850cc Carb) - 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 bar and producing a regular flow of gas fuel for the engine's need. 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 a 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 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).







Petrol (Gasoline) Solenoid - Carburetor Only


Petrol (Gasoline) Solenoid valve is used to cut off petrol supply to the engine when it is run on CNG. The petrol electro-valve (carbureted engine only) is placed between the gasoline filter and the carburetor and interconnected by gasoline resistant rubber hoses and metallic clamps. When installing the petrol electro-valve, special care must be taken as to the direction of the fuel flow, indicated by a small arrow on the valve. As in the case of other components, the electro-valve must be fastened to the vehicle by means of the corresponding bracket, taking care that it is not installed over any other electric part that may create a spark or that the flow of gasoline in the hose does not run towards any element that may create a spark.


Picture Source: www.landirenzo.com  


Petrol Solenoid

 Petrol (Solenoid) Solenoid valve (carburetor vehicle only)



In view of the above, the clamps that are placed on the petrol electro-valve require the greatest care and attention. It is most advisable to check all the other clamps of the petrol system, particularly those between the petrol pump and the electro-valve, because when closing the flow of petrol the pressure is greater than normal at that stretch.






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.








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








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




Timing Advance Processor (TAP) - Joker-N for most Caburetor Vehicles










S.O.S Method For Carburetor NGV Vehicle Start-Up


In this instance, we strongly recommend that existing NGV Users (with carburetor NGV vehicle) should use the S.O.S (Step-Switch On-Start Ignition by Dr. Xander Thong) method to start-up their vehicles. By stepping on the accelarator at half distance, the Throttle Valve will be open at half Open-Throttle position. Next following action is that you are to switch on the ignition (without cranking up), and allowing gas to be injected directly into the engine manifold (an unobstructed fueling). Most NGV electronic kits have an Easy-Start function, that inject a pre-mixed fuel into the engine for easy engine start-up. The final action is the start-up or crank-up the engine.


Having the accelerator depressed half-way (throttle valve open up half as well), and switching on the power is propagating pre-mixed fuel straight into the combustion chamber for easy-start. And finally, you can crank up the engine as the last sequence of S.O.S action.


Picture Source: www.ngv.com.my  

SOS Method

Step-SwitchOn-Start or S.O.S Method for Carburetor NGV Crank Up



S.O.S Method  is able to assist existing NGV Users to starting up a carburetor-type NGV vehicle. The reason is simple logic. It is almost impossible to start-up the engine, when the Throttle Valve is kept at almost Closed position. It is necessary to open-up the Throttle Valve to allow pre-mixed fuel to enter directly into the engine. Unlike petrol (gasoline) start-up, CNG-NGV requires an unobstructed gas flow (or open-throttle).
















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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