Natural Gas

Natural gas is a natural mixture of gaseous hydrocarbons made up of at least 80% methane (CH4) with slight amounts of ethane, propane and butane. Within the UK, natural gas is mainly used for electricity generation and heating.

Natural gas can be used in a modified internal combustion engine to provide motive power. The gas makes an ideal fuel for spark-ignition engines due to its high octane rating, low levels of volatile organic compounds and due to the fact that it mixes easily with air prior to combustion. This offers lower idling speeds, better performance, easier cold starting and a more complete combustion, all of which help to reduce exhaust emissions. Due to the low number of gas refuelling stations most natural gas cars are bi-fuel conversions. These are able to operate on gas or petrol, the fuel being selected at the flick of a switch.

There are many advantages in using natural gas. They include lower engine noise as well as longer engine life as a result of the fuels clean burn characteristics that lessen engine stress.

Conventional (petrol) three-way catalytic converters continue to be used for the majority of natural gas bi-fuel cars. Whereas, dedicated gas vehicles utilise catalysts which are optimised for methane, cutting vehicle emissions further.

The way fuel is stored is the key difference between natural gas and conventional cars. As natural gas is gaseous at room temperature and pressure, it is stored as compressed natural gas (CNG) or as liquefied natural gas (LNG), the latter cooled to -190 degrees Celsius. CNG is the most usual option for cars, as the gas is stored in pressurised cylinders (at 200 bar), located in the boot space. Due to the extra cylinder the amount of luggage which can be carried is limited.

Natural gas is a tested green car fuel. Presently, there are more than 1.2m vehicles using natural gas internationally in Italy, Argentina, the former Soviet Union, Canada, the USA and India. In the UK, there are about 500 natural gas vehicles being used. A small proportion is bi-fuel natural gas cars or vans, most of them are dedicated (mono-fuel) heavy-duty vehicles (buses and lorries).

Q. What are natural gas cars like to drive?

On the whole a natural gas car is almost the same to drive as a conventional one. The controls are more or less the same; starting, engaging and stopping the engine are undertaken in the normal way. The main additions include a switch which is located by the gear lever or on the dashboard, enabling the driver to opt for gas or petrol operation, with a fuel gauge which shows the remaining amount of both fuels.

In contrast to petrol operation, bi-fuel car drivers may notice a slight loss of power at full throttle when in natural gas mode. In the majority of driving conditions, the difference is barely noticeable. Dedicated natural gas cars perform at the same level as conventional fuel vehicle.

Q. How do I refuel a natural gas car?

There are two types of natural gas re-fuelling systems: fast-fill units which use high pressure compressed natural gas to refuel vehicles in a few minutes; slow-fill compressor units 'trickle charge' a vehicle or a couple over a period of 5-6 hours. For refuelling purposes, a flexible hose is connected between the dispenser and the car is fixed into place creating a sealed system. For fast-fill systems, the amount of gas needed is then selected prior to being automatically dispensed; whereas, slow-fill units carry on operating until the tank is full or filling is interrupted by the user.

There are few gas refuelling stations in the UK for natural gas. Although the UK has the advantage of having an extensive national gas grid, at present there are only about 30 CNG filling stations, with only 12 of them being fast-fill stations accessible to the general public. On a more upbeat note, slow-fill units are currently being developed for home refuelling; the requisites being a natural gas supply, off-road parking (a drive or garage), as well as a suitable location for the compressor.

For the locations of UK natural gas stations, check out the Energy Saving Trust website.

Q. Are Natural Gas Cars better for the Environment?

In principle, carbon emissions from natural gas cars are lessened by the fuel's low carbon content and high octane number. Other than carbon dioxide, methane is a key greenhouse gas. Hence, methane life cycle emissions need to be accounted for when estimating the effect of natural gas cars on global warming. Accounting for carbon dioxide and methane emissions, natural gas bi-fuel cars (and car-derived vans) are improving in terms of greenhouse gas emissions (per mile); they are about 10-15% in contrast with those using petrol. Therefore, natural gas car greenhouse gas emissions are around the same as those for light-duty diesel vehicles.

Other than methane, regulated emissions (per mile) are lower for natural gas cars than others. Huge emission reductions are produced due to mono-fuelled (dedicated gas) engines.

Q. How much do natural gas cars cost to own?

Certain ownership costs for natural gas cars are higher than for their petrol counterparts. This is mainly as a result of the higher purchase price (should it be bought new from a manufacturer) or due to the cost of converting an existing car. Approximate costs for cars or car-derived vans are 1500-2500. Should you need a refuelling compressor unit it will cost 2,000 for a slow fill system.

You will save 50 a year for vehicle excise duty in contras to a petrol car. Given low fuel availability, dedicated gas cars perhaps have a higher than average depreciation rate, as there are not many NGV buyers.

Q. How much do natural gas cars cost to run?

The costs for NGVs are presently the same as petrol cars.

Previously the switch to NGVs has been dominated by fuel cost savings; however, due to recent increases in the cost of natural gas at the 'pump', the costs are now on the whole comparable.

The main variable cost for drivers in London is the congestion charge. Given the daily 8 charge, you can save up to 2000 p.a.

Q. Where can I Purchase A Natural gas car?

Natural gas cars are basically conversions of normal petrol cars; converted by the manufacturer at the factory or retrofitted upon being sold as a new car.

You will find details of car manufacturers and approved converters (OEMs), those who supply natural gas cars, on the Energy Saving Trust's PowerShift Register. They include models available from the main manufacturers like: the Vauxhall Zafira and Combo van, three models in the Volvo range: the S60, S80 and V70 and the Ford Focus. Many companies are willing to convert your petrol car to natural gas after sales.