Autogas and the Environment

Keeping it clean

Autogas is a clean fuel. It's contribution to pollution is considerably less than either petrol or diesel. To explain why it will be necessary to become a bit technical, but this will be kept to a minimum.

Petrol engines - why they pollute

Petrol is drawn in to the engine as a  liquid spray with differing degrees of success. To burn completely the droplets must be very small, complete combustion is virtually impossible. The net result is that the exhaust contains unburnt fuel together with various other toxic emissions. 

Catalytic converters

To overcome this, three way catalytic converters have been fitted to all cars in this country since the early 1990s and have had a dramatic effect on pollution. However they are not a complete answer as they attempt to chemically clean the exhaust rather than get rid of the problem at source.

Contrasting petrol with propane

For petrol to burn properly it must be fully vapourised, and it takes a lot of heat (about 400 deg F) to achieve. This is quite simply not possible - even with the hottest of engines. If you also take into account that many journeys are short enough that the engine does not achieve working temperature, it can be understood that petrol is not the ideal fuel. 

Propane on the other hand becomes a vapour at -43.7 deg F so even on the coldest winter day the engine will have gas available which can burn completely. The choke (or cold start enrichment) becomes  a thing of the past as there is no need to compensate for all the fuel that is not burnt by bunging loads more in to the engine! This is one reason why  petrol vehicles are more economical on long runs than when just "popping in to town."

Carbon Monoxide is a gas that depletes oxygen in the body, engines running on lpg are up to ten times cleaner, than those running on petrol.

The Propane engine will also emit lower levels of oxides of nitrogen (NOX) because the gas does not burn as hot as petrol, and NOX emissions tend to go up or down in relationship with temperature.

It is un-deniably true that petrol engines have cleaned up their act over the last few years as already discussed, however because Autogas is on the lighter end of the Hydrocarbon scale it reacts differently than petrol. A major problem in a number of cities is smog. This is produced by a photo-chemical reaction between the exhaust gases and sun-light , Hydrocarbons at the lighter end of the scale take much longer to convert to smog, and therefore gas engines are environmentally friendly in this aspect too.

It is precisely for these reasons that duty on Autogas was lowered a few years ago , and the now defunct Powershift programme existed.

Finally because LPG is much kinder to the engine's bottom end, the lack of fuel residue can  reduce the need for oil changes and other service parts on such a regular basis. There is a trade off however as on some vehicles there is increased wear to the valves. 


 Compared to Petrol   Compared to Diesel
 75% less Carbon Monoxide *   90% less particulates *
 85% less Hydrocarbons  *   90% less Oxides of Nitrogen *
 40% less Oxides of Nitrogen *   70% less Ozone forming potential *
 87% less Ozone forming potential *   60% less Carbon Monoxide *
 10% less Carbon Dioxide *   

* Based on  tests undertaken at Millbrook


  • What is Autogas? - What it is, where it comes from.  
  • Overview             -  For those with a short attention span;; 
  • Ready reckoner   -  Calculate the savings you will make on fuel purchases.  

  • History.               - Learn about this fuel. (Its been around longer than you think)

  • Environment        - Why Autogas is a "green fuel."

  • System types      - Look at the equipment.

  • Advantages.        - Looks at advantages and dis-advantages

  • Fuel availability   - Where to fill up, and a link to the LPGA.

  • Prices.                 - How much your conversion could cost               

  • FAQs                    - Frequently asked questions.


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