The most number of cars sold in India continue to be small petrol hatchbacks, or cars below Rs. 4 lakh, where there are no diesel options available. However, with the price of petrol increasing rapidly compared to diesel, and with the price differential now being close to 70%, small petrol car buyers are being hit hard when it comes to running costs.

The only option then is to switch to alternate fuels such as CNG or LPG, which are priced much lower. In Delhi, CNG is at Rs. 38.35 a Kg and LPG is at Rs. 42.70 a liter. Petrol is priced at Rs. 68.46 a liter, while diesel is at Rs. 41.32 a liter.

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CNG or LPG: How to choose?

Choosing whether CNG or LPG will suit your small petrol car like a Wagon-R or Alto better, involves first looking at these common concerns:

–          Does your city have a CNG or LPG network? Some cities like Delhi have both CNG and LPG available, while some like Bangalore are LPG only. This is the primary deciding factor when opting for either CNG or LPG.

In many towns and cities which do not have LPG stations, people tank up LPG using domestic gas cylinders. While such a thing is possible, it high strongly recommended that such practices are not followed. They are a safety hazard.  And amount to theft of subsidized domestic gas. Also read: CNG vs. LPG vs. Petrol vs Diesel: A simple 4 step guide to deciding which fuel type works best for you

–          Do you want luggage space? In a car like a Maruti Alto or a Wagon-R, fitting a huge 12kg CNG cylinder will leave no space for any luggage at all. However, if you opt for LPG, the size of the cylinder is smaller, and you get toroidal cylinder designs that fit snugly into the spare wheel well of the car. CNG cylinders have to be bigger because they are under high pressure as they have to store compressed gas and because CNG is much less dense than LPG. LPG cylinders are thinner and smaller because the fuel is in liquid form inside the cylinder and stored at much lower pressure.

–          Do you have adequate filling network? The problem with CNG-driven cars is that the network for CNG is based on a pipeline with gas supplied from a central pumping station under high pressure. Based on this pressure, some pumps can fill in a more gas, while some can’t. Therefore the pumps that usually have better gas pressure (therefore getting in more kilos of gas into the cylinder) usually have a long line of cars waiting for their turn. LPG dispensing, on the other hand, is done from storage tanks at the pump itself and not dependent on pipelines or gas pressure like CNG.

–          How long are you prepared to wait to fill gas? It takes between 4-5 minutes to fill each car with a tankful of CNG. If you are the 10th car in a line, you are looking at close to 40 minutes of waiting for one tankful of CNG. LPG, on the other hand, has a much faster filling process and takes about 2-3 minutes at the most – just like either petrol or diesel.

However in many cities, the CNG stations outnumber LPG stations. So in a metropolis as big as Delhi, you’l find a CNG station in every part of the city but LPG stations are few and far between. Read more: Different kinds of CNG kits: Advantages and disadvantages

–          How much power are you willing to lose? Small cars like the Maruti Alto 800 put out just 46 bhp of power and 62 Nm of torque. With CNG you’ll lose about 15% of that peak power, which would make it equivalent to a 39 bhp petrol engine. On LPG the power loss is a little less, only about 10%, which makes it equivalent to a 41.5 bhp petrol engine.

–          My car has low ground clearance. Will it bottom out? CNG tanks are much bigger and heavier than LPG tanks. A 12kg CNG tank filled with 10 kg gas weighs close to 100kgs. All that weight behind the rear axle means the car will bottom out quite frequently, especially with 5 on board. Adding spacers to the rear suspension is a cheap and effective solution but at the cost of ride quality. LPG kitted cars fare better in this respect.

–          How about I install an LPG kit and run it on CNG? This is unfortunately not possible. Both fuels, though “gases” for the layman, have vastly different physical properties. You cannot run an LPG kited car on CNG or vice versa.

Calculate your return on investment

Choosing LPG or CNG also is a function of how much you are willing to spend on the conversion. CNG kits are slightly more expensive than LPG kits owing to an additional number of parts and the CNG storage tank. For instance, a good LPG kit for a car like an Alto or Wagon-R will cost about Rs. 25,000 while a good sequential CNG kit for the same will cost about Rs. 40,000. Read more: Which offers more savings – CNG or LPG?

The initial purchase cost is cheaper for LPG. But it is a completely different story as far as running costs go. A car which gives 14kmpl on petrol will average around to 20km/kg CNG. But on LPG, expect a realistic 12kmpl, with the savings coming only from the lower cost of fuel. CNG makes more sense for those with hefty running. Also read: Both CNG and LPG deliver savings over petrol, but which one offers more?

Keeping the above points in mind, decide whether you want to convert your small petrol car to either CNG or LPG. If you have already done so, please share your experience with the CarToq community.