What do I have to expect if I choose a CNG car?


@Lauren M.

The OEM has commercialised dual-fuel models for about 20 years: petrol and methane or single-fuel that is only methane.

At the beginning the production of these cars didn’t directly take place from the same car manufacturer, but the transformation was entrusted to external fitters, who installed the system on the car with the original petrol version.
Basically they were solutions very similar to the aftermarket.

Remaining in the Fiat brand, on which I can give my direct contribution, the first car, designed and produced directly in the factory, was the Multipla in both bifuel and mono-fuel version.

The production of the car was organised in this way:

  • The body was produced on the guidelines of the basic versions, with the only variant of the three under-floor transverses for fixing the cylinders;
  • it was painted on the normal line and then sent to the Arese factory, to be completed in all its parts.

The solution found to mount the cylinders under the floor allowed to obtain great advantages:

  • great methane autonomy: 450 km for bifuel, 620 for mono-fuel against max 250 km of solutions with a cylinder in the trunk;
  • the volume of the car trunk basically unchanged;
  • maximum safety in case of accidents;
  • full compliance with ECE ONU R110 norm for natural gas vehicles (not required).
2012 Ram 2500 Heavy Duty CNG with bi-fuel capability

2012 Ram 2500 Heavy Duty CNG with bi-fuel capability—powered by compressed natural gas or gasoline. @FCA


The essential components for a petrol / methane dual fuel car are:

  • cylinder(s) including valve (for ECE ONU R110 mandatory solenoid valve with fuse pad and pressure relief valve);
  • metal piping from the cylinder to the engine compartment connected to the pressure reducer;
  • pressure reducer;
  • low pressure tube up to the injector rail;
  • methane injectors on intake manifold;
  • filler neck for methane refuelling;
  • piping from the nozzle to the cylinder;
  • potential pipe from cylinder to cylinder when these are more than one.

I would like to underline that there would be some work in the production phase, not obligatory according to current legislation, which would guarantee an optimization of consumption and performance of methane engines, which no aftermarket transformation could offer.

Unfortunately for reasons related to the containment of production costs, until now, these optimizations have not been taken into consideration:

  1. valves and valve location specific to methane. (They guarantee the non-wear of these components, over time, for high methane journeys);
  2. specific catalyst for methane. (From tests carried out on the Multipla if the petrol remains after 30/40,000km the exhaust emissions are out of bounds);
  3. gear ratios depending on the natural gas engine performance.


In my experience, further development of methanisation would be necessary to ensure maximum benefit.
What we could call “Ideal Methane Car” should have the following additional features:

  1. natural gas autonomy at least 500km;
  2. eight-cycle engine optimized for methane;
  3. compression ratio around 14;
  4. ignition advances;
  5. specific phasing;
  6. petrol operation with 15 litres tank with reduced performance to avoid detonation when the methane ends (in this case petrol is considered as an emergency and therefore not subject to emission tests);
  7. No penalization for the interior volumes of the passenger compartment and the boot.



Methane, responsible for 18% of the increase in the greenhouse effect, is a gas present in the Earth’s atmosphere in concentrations much lower than those of CO2 but with a global warming potential that is 21 times higher, indeed it has CO2e = 20 (equivalent CO2 greenhouse effect coefficient).

Its use for fuel-transport doesnÕt produce direct emissions into the atmosphere, indeed its combustion doesn’t generate particulate, while for the CO2 there is a reduction of a few percentage points compared to diesel and petrol.
Moreover, being transported through methane pipelines, it doesn’t produce any impact on surface traffic and, unlike petroleum products, doesn’t require large deposits for storage.



Positive aspects

  1. Very low cost of the methane (about 1€/ kg, which is equivalent to about 2 litres of petrol 1.5€/ l) the cost per km is less than half of that of gasoline.
  2. With no added additives, exhaust emissions are less polluting.
  3. Usually it is not subject to traffic blocks for environmental reasons.
  4. Not affected by rigid external temperatures.
  5. The additional cost of the system is amortised in a few thousand kilometres.
  6. It benefits from a significant reduction of the road tax.

Negative aspects

  1. The distribution network is quite limited. In Sardinia there are no distributors while in some European countries there are very few distributors.
  2. Being a gas, it requires large volumes of cylinders that are not easily inserted without major modifications to the body.
  3. For the aftermarket solutions, as well as the almost complete loss of the trunk, It changes the distribution of weight, especially on the rear axle, so that critical issues could happen at full load both with the structural rear suspension and the road holding due to a non-optimal braking distribution.


My personal opinion is that a methane-powered car is very good and, therefore, recommended, if you have a nearby petrol station.


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Translated by Federica Izzo

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