LPGinfo.co.uk

What is LPG?

LPG (Liquefied Petroleum Gas) is a natural hydrocarbon fuel made up of propane and butane. LPG has several applications which include domestic or agricultural heating and vehicle fuel (often referred to as ‘Autogas’).

Why convert?

A vehicle can be converted to run on Autogas (as well as existing petrol) which makes it both cheaper to run and more environmentally friendly. It is then referred to as a ‘bi-fuel’ vehicle.

LPG can be purchased (in the UK) from 45 to 65 pence per litre, making it much cheaper than petrol.

If you are considering an LPG conversion then there are many things that you should know and consider. A lot of these I have learnt myself through my own journey of discovery with an awful and unsafe LPG conversion by a 'reputed' LPGA Approved Installer (The LPGA is a UK trade organisation for LPG).

LPG versus Diesel and other current fuels

Modern diesels (especially BMWs) have come a long way in recent years. The BMW 320D, 330D, 335D, 530D, 535D are all very rapid cars. However, in my experience with the 320D and 530D models (E46 and E39), any savings made via extra diesel MPG are negated if you suffer a turbo or injector failure. Turbo failure can also damage the cats and although injectors can be reconditioned, this process is very expensive.

It has recently emerged that there appears to be a serious problem with the E46 BMW 320D (and the E46 184 BHP 330D (auto), E46 204 BHP 330D and E60 530D less so) suffering from swirl flap failures. The inlet manifold contains variable swirl generating flaps which are prone to braking off (or the butterfly valve fails) and being injested by the engine - a very expensive bill results! They are designed to reduce exhaust pollutions and are found on the M47 (2.0d) and M57 (3.0d) they are found on models with auto gear box (3/2000 onwards). On newer M47N and M57N/N2 (E60/E61) flaps are on all models (also with manual gear box).

The following research has been carried out by smorris_12 on BMWLand:

The above problems, however, are not limited to BMW diesels as other manufacturers appear to be employing these new technologies to improve the performance and fuel consumption of their diesel vehicles too. Whilst it is understood that 'speed to market' is important, one wonders whether sufficient testing has been carried out at the design engineering stage.

There is no doubt, however, that diesel is now a force to be reckoned with but a lot of this choice is about the total ownership experience and what kind of buyer you are. I, personally, do not buy new and rarely sell quickly. I travel a lot for work and would prefer one decent car which I will make good use of. As a result, I am not worried about re-sale value. I also wanted a V8 before more uncertain times hit the world in terms of the economy, environment and fossil fuels in general. More than anything, I enjoy filling my gas tank with 40 GBP of LPG and it lasting 350 miles - a V8 for Nissan Micra money.

Further information about LPG / Autogas

There is lots of information about LPG on the Internet, however, the following is particularly useful:

Automatically translated from German (may contain errors).

Source: © Sven Geitmann: http://www.hydrogeit.de/geitmann.htm

Environmental advantages of LPG opposite gasoline with the limited pollutant emissions:
+ reduction of CO2 over up to 15%,
+ reduction of HC over up to 60%,
+ reduction of CO over up to 80%,
+ reduction of NOX over up to 80%,
+ particles not discharged with LPG.

Beside the limited pollutants (CO, HC, NOX, particle) there are so-called not-limited pollutants (e.g. SOX, NO2, benzene, formaldehyde etc., which develop with the burn of fuels.

Environmental influences of gasoline, Diesel, natural gas and liquid gas:

Natural gas, as fuel, is the best of the comparison. Liquid gas is slightly better than the average. Gasoline is slightly worse and Diesels worse than the average. The exhaust gases of Diesel engines exhibit a high carcinogenic effect potential compared with the others (LPG, CNG and gasoline).

The carcinogenic effect of the Diesel exhaust gases is on the discharged particles and partially the substances responsible to it (e.g. Aldehydes to lead back PAH). By the introduction of particle (particulate) filters for diesel engined vehicles the particle emission (per driven kilometer) and with it the carcinogenic effect can, comparably, be lowered. In regards to soot, modern diesel engined vehicles discharge less large particles, small particles are however more easily penetrate the lungs and settle there.

With petrol engines there are the polyzyklischen aromatic hydrocarbons (PAH) with carcinogenic damage potential beside benzene. These pollutants are reduced by the use of catalysts over up to 90%. [Lack village, I., 1999]

Environmental advantages of LPG with not-limited emissions are:

• The reduction of the exhaust components, which are responsible for smog, over up to 80% in the comparison to the petrol engine, [DVFG, 2000]
• The reduction of the output of substances, which are relevant for the greenhouse effect, over up to 20% in the comparison to the petrol engine.
• The reduction of the toxic and emissions injurious to health, as e.g. of polyzyklischen aromatic hydrocarbons, aldehydes, benzene, toluols etc

Cold weather starting

A particularly critical phase with regard to pollutant output is the start and the warming-up phase. Since more are shorter as half of all drives than 7 km, in this time however a majority of the emissions to be discharged, applies for this phase a special attention

In cold condition the engine oil is still high-viscosity and cannot not in full measure its lubrication function notice. A part of the heat of combustion is derived for the heating up of the engine, so that for the actual achievement yield at the beginning of less energy for order stands than with operating temperature. Within the wall range by the cylinder and the cooling agent warmth is derived, whereby the necessary burn temperature is not reached and relatively much hydrocarbons is set free. This phenomenon partially one against-works, as the air relationship is reduced. One speaks of the fact that the engine starts in the fat range.

Since in this case more fuel is present, than is necessary for a stoichiometric burn relationship, a part of the fuel is only partially burned again discharged unburned or. In addition increased pollutant values come off thus that the catalyst is not yet on operating temperature and cannot therefore its function of the pollutant reduction not fulfill.

An advantage of LPG engines opposite petrol engines is that the fuel is present already gaseously and therefore a better mixing with air is possible. With liquid fuels such as gasoline the evaporation rate is at small temperatures so low that only a relatively small quantity of gasoline vapors is present. Since gases and gas mixtures are more easily entzündbar than for example gasoline droplets, no or only small problems arise with liquid gas. A Anfettung as in the gasoline enterprise with nearly sixfold normal amount of fuel is not necessary therefore. The liquid gas/air relationship is almost always identically and independent in the comparison the petrol engine relative to with the LPG engine of the ambient temperature.

Already available investigations about cold weather starting show that a Otto engine with gasoline discharges as fuel substantially more pollutants at small temperatures than with liquid gas. In the course of a modified European Testzyklusses the pollutant emissions were measured with gasoline and liquid gas enterprise in a temperature range from -7 to +22 °C. The modified test cycle differs from the standard test by the fact that in it no no-load operation and/or warming-up phase of 40 seconds lies between start and beginning of test. The CO emissions in the gasoline enterprise rise strongly and the HC and NOX emissions rise somewhat, as soon as the ambient temperature drops under T = 10 °C. Clear changes as a function of the temperature are however not to be registered in the LPG enterprise. [Hollemans, B., 1999]

The life span of the different vehicle components represents a substantial cost factor. That national according to Association the engines two until three times live Propane gas so long like petrol engines. This comes among other things by the fact that compared with petrol engines less aggressive acids and carbon deposits are present, the oil not so strongly watered and the increase of pressure in the combustion chamber does not run so steeply. [U.S. DOE, 1998]

Regarding the durability of spark plugs there are different data. On the part of a qualified Autogas Installer, it means:
The replacement of spark plugs before the mileage recommended by the vehicle manufacturer is necessary only with vehicles, which are equipped with a venturi plant. With these usually older vehicles the premature change is necessary, in order to reduce the danger of backfire. With vehicles, which are equipped with newer, gas injection systems so mentioned, the danger of backfiring and a premature exchange of the spark plugs does not exist and is, therefore, not necessary. Since liquid gas is however not as 'ignition joyful' as gasoline, it can occur that it comes by the normal wear of the spark plugs in the liquid gas system rather to ignition misfires as in the gasoline enterprise. In this rather rare case the spark plugs would have to be if necessary in former times replaced.

Pro and cons

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