Different kinds of CNG kits: Advantages and disadvantages

As petrol prices sky-rocket, more buyers are keenly eyeing conversion of cars to run on dual-fuel systems – CNG and petrol or LPG and petrol systems, where the car can run either on petrol or CNG/LPG. CNG conversion kits can be retro-fitted on almost every petrol car sold in India, but one has to make sure you’re getting the right kit.

Also, not all cars can have CNG kits fitted on them. The Registering Authority of the state in which the car is registered has a list of cars that are “CNG approved”. If your car is on that list you can go ahead and convert the car to run on CNG. If not, you won’t be able to get the fuel use change stamped on your RC, which is mandatory by law. Cars in Delhi, for instance, have to meet Euro II emission norms to be approved for CNG conversion – which means most cars that have been manufactured post 2002 only can be converted and not older cars.

However, when choosing a CNG kit for your vehicle, the primary decision you have to make is whether you want to buy a Sequential Kit or a Venturi Kit. Here’s how the two are different:

Venturi Kits

Venturi CNG kits is a term that refers to the CNG mixing unit and how it delivers gas to the engine. Venturi kits are generally cheaper to install and less complex than sequential kits. A venturi kit behaves like a carburetor or “venturi” which dumps a fixed amount of gas based on throttle input directly into the intake manifold of the engine. A venturi-type CNG kit can be applied on any type of vehicle, whether it’s carburetor driven or fuel-injected, with or without an ECU

This type of CNG delivery is not very accurate and hence there are issues of incorrect tuning that happen with venturi-type CNG kits.

Advantage of venturi-type CNG kit

The advantage of a venturi-type kit is the low cost of installation. For a small car owner, like a Maruti Wagon-R for instance, a venturi-type CNG kit along with a 12 Kg cylinder will cost about Rs. 35,000-Rs. 45,000 depending on the brand. There is no separate ECU for the CNG system and hence no complicated wiring or sensors. It’s a relatively simple system to install.

Disadvantage of a venturi-type CNG kit

The disadvantage of a venturi-type CNG kit is that since it dumps a fixed amount of gas into the intake system, there are issues of loss of pickup and stalling occasionally, when there is too much or too little gas in the system. It needs to be frequently cleaned and tuned up accurately, which not everyone can get right

Sequential kits

Sequential CNG injection kits are a much better option for your car. This is because the gas flow is controlled by injectors that directly fit into the intake manifold next to the petrol injectors. Gas flow is monitored and adjusted electronically by a separate ECU for CNG, just like how the petrol ECU controls petrol flow. Sequential injection CNG kits can be installed only on vehicles that have electronic fuel injection systems.

For a Maruti Wagon-R for instance, a sequential injection CNG kit is a much better option as it emulates the same kind of injection pattern that petrol does. However, the kits are a lot more expensive. A Landi-Renzo, BRC, or Lovato CNG kit for the Wagon-R costs about Rs. 60,000-Rs.70,000 including a 12-Kg CNG cylinder in the boot.

Advantage of sequential kits

The benefits of a sequential CNG injection kit are plenty. You get more accurate CNG injection which results in better mileage and better performance, although CNG generally has a drop of about 15% in performance owing to its higher octane rating and lesser combustibility than petrol, and performs better on high-compression engines only, which aren’t common on normal cars.

Disadvantage of sequential kits

The only significant disadvantage of a sequential kit is the initial purchase cost, which is nearly twice that of a venturi-system. The other minor disadvantage is that it is more complicated and installation requires some drilling and modification of the intake manifold, unlike the venturi-system that requires less drilling.

Open-loop and Closed Loop sequential systems

Another thing to consider while choosing a CNG kit is whether you want an open-loop system or a closed-loop system. What this means is whether your CNG kit takes feedback from the oxygen sensor placed in the exhaust system and transfers that back to the ECU or not. There are advantages and disadvantages to both these systems.

Closed-loop system

A closed loop system is one where the O2 sensor or lambda sensor in the exhaust gives feedback to the ECU controlling the CNG gas flow, and tells it whether exhaust emissions are within permissible limits or not. The ECU then regulates the gas flow accordingly to prevent too much pollution.

Advantage

The advantage of a closed-loop system is that you get precise emission control and will be doing the environment a favor. You also get slightly better fuel efficiency because it keeps the gas injection at an optimum point.

Disadvantage

However, not everyone is happy with a closed-loop system, especially if one is used to superior performance while driving on petrol. The reason is there is a marked drop in performance as the CNG ECU tries to inject only the optimum amount of gas to prevent excessive exhaust emissions. This means that you may not get the kind of acceleration you want, when you need it.

Open-loop system

An open-loop system is one where there is no feedback taken from the O2 or lambda sensor in the exhaust, allowing the car to accelerate and inject more gas at will, without the lambda sensor acting as  a nanny.

Advantage

On older cars where there was no oxygen sensor in the exhaust system it results in cost saving, as one does not need to buy an O2 sensor (that costs about Rs. 4000). On newer cars, having a lambda system, installers often do not connect the sensor to the ECU, leaving it taped up, therefore remaining an open-loop system. Because it’s left this way, there is no restriction on the amount of CNG that can be injected into the engine at any given temperature, allowing for better performance and pick up.

Disadvantage

However, an open-loop system has its inherent disadvantages. One is the higher exhaust gas emissions that occur as there’s nothing to monitor emissions in the system. And two, a more significant concern is the heat build up in the engine. Open-loop systems tend to run a lot hotter because of no monitoring of exhaust gases and this can damage exhaust valves of the engine.

Ideally, one should always choose a closed-loop system, even if it means a slight compromise in performance, as its better for the environment and for the engine.

Popular RTO approved CNG brands in India

There are at least 20 brands of approved CNG kits in India. These brands have both venturi-type and sequential kits for a list of cars (that have been vetted by the RTO). These brands include Landi-Renzo, Zavoli, Tomasetto, Lovato Autogas, Longas, Tartarini, BRC, Bedni, Bugatti, Unitax and SKN. All these kit makers have tie-ups with various car dealers by brand. So some Maruti dealers may supply only BRC kits, while other Maruti dealers may supply only Lovato kits.

If you are shopping for a CNG kit, it makes sense to visit multiple car dealers and figure out which one is the best for you. There are also independent garages that have multiple brand kits available, but make sure you check out the installer’s reputation and speak with other customers before opting to get a CNG conversion done by an independent garage. Also ensure that the dealer does all the paperwork for you such as getting the change of fuel endorsed in the registration certificate of your vehicle.