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It's safe and it's an 'alternative fuel'

12th June 1982, Page 49
12th June 1982
Page 49
Page 50
Page 49, 12th June 1982 — It's safe and it's an 'alternative fuel'
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Which of the following most accurately describes the problem?

Graham Montgomerie goes into the background and the why's and wherefore's of lpg — a fuel that is making the grade across the world,

ALTERNATIVE FUELS" have aen the subject of a lot of iscussion in the past.

"Alternative" in the automove context means anything bich can replace petrol or diel.

A great deal of research is oing on into such energy )urces as powdered coal, hyan, alcohol derived from vegeIble matter and so on.

One alternative fuel which is eailable now is liquefied petrourn gas or lpg for short which sold mainly for its potential )st savings in the short term. n the long term, however, it m be used by vehicles which wently use up petrol or dery lus extending the world's re)urces of these two fuels.

One of the companies volved in the lpg market is Sox (UK) Ltd which is a part of the .ench Matra Group, a vast )ncern whose interests include ansport, tele-communications pmputer technology and ectronics.

Sales director Al Lighton is opriistic about the future of lpg r automotive use even though ; potential growth has been hit / the present stabilising of peal prices. But first some techniil background...

Liquefied petroleum gas is a Pup term for propane, butane Id mixtures of these two gases. Ithough gaseous at ambient mperature and pressure, for Jtornotive use they are liquexl by compression.

Liquefied petroleum gas comes from two distinct sources. First, from the processing of crude oil in refineries, and second by extraction from natural gas streams. The former has been the traditional source of lpg for the majority of consuming countries outside the United States and this includes the UK. However, we now have two terminals at Immingham (Conoco) and Felixstowe (Calor) to bring it in from the North Sea oil well heads.

As I mentioned earlier, lpg can be a mixture with the proportions of propane and butane varying from country to country and also varying due to the weather. Some of the major users like Holland and Belgium average around 50 per cent of each gas in their lpg. I say "average" as this is a case where the proportions are varied to suit the climate.

Butane is comparatively poor on cold starting, but it has a higher calorific value and so is preferable as an automotive fuel as there is less energy loss compared with petrol. Propane has a lower boiling point and thus becomes a gas more readily. Thus the Dutch mixture varies from 60/40 butane/propane during the summer to the reverse during the winter.

Propane is more readily available in the UK and thus for all practical purposes it can be assumed that all UK lpg is virtually 100 per cent propane.

Saudi Arabia is currently the world's largest exporter of lpg averaging over five million tonnes annually. Other Middle East countries with significant exports of lpg are Abu Dhabi, Iran and Kuwait although none of these countries individually produces anything like the Saudi quantity. Algeria is currently expected to become the world's largest exporter of natural gas but only one third of this will be lpg. During the 1980s Algeria's export of lpg is expected to reach 10 million tonnes a year.

Several countries already have significant automotive lpg markets, including Holland and Belgium — in Holland, for example, 400,000 vehicles out of the total of three million have been converted to run on gas. In the UK and other European countries the lpg markets are in various stages of development.

Lpg is claimed to have a number of advantages over conventional hydrocarbon fuels.

The main advantage is usually emphasised as one of cost and I will return to this point later on. The other advantages are technical and include a high octane quality without lead, good volatility and cleanliness of the fuel.

To run spark ignition engines on lpg there are three approaches which may be folI owed. Currently the most popular is the dual-fuel engine which is converted to run on lpg while retaining the existing fuel system and carburettor. This is particularly useful for countries like the UK where the lpg sector is comparatively small and gas sites few and far between.

The best of these approaches is where the engine is designed and built by the manufacturer for exclusive use with lpg and thus can be designed without the need to compromise. In addition to the obvious differences in the fuel system, the lpg-optimised engine would probably have a higher compression ratio, a larger bore induction system, improved valve and seat materials and an improved ignition system.

The final choice is where the existing petrol engine is again converted but this time to run exclusively on lpg.

Current designs of dual-fuel conversion systems have a fuel selector to switch from petrol to lpg and back again. The lpg is drawn from the tank in liquid form and passed through a heat exchanger, using coolant or exhaust heat to vaporise it. From here it passes to a first-stage pressure regulator which reduces and stabilises the gas pressure and then to a secondstage regulator which feeds the gas carburettor.

There are disadvantages associated with the use of lpg, however. There is a power penalty because of the reduced amount of air the engine can breathe as the gaseous lpg displaces more volume than petrol metered as a liquid and so because, in a petrol engine, the latent heat of evaporation of the sfuel increases the charge density as the petrol evaporates and thus cools the mixture.

It is possible to 'recover some of this lost power by engine design changes but these are usually too major to be justified by the size of power loss. Increasing the compression ratio and adding a turbocharger are two such examples.

Fuel consumption also suffers when lpg is used. This obviously varies from engine to engine but as a rule of thumb the same engine running on lpg will have a 15 per cent worse fuel consumption than when using petrol. Solex experience in the field has shown that the losses on an lpg engine are higher on full throttle motorway work than with stopstart traffic operation.

On the engine durability side, there are claimed to be a number of advantages associated with using lpg although, as before, there are also disadvantages.

Longer engine life is claimed as a result of reduced cylinder bore wear during cold starting because lpg, being gaseous when it enters the cylinders, does not wash the lubricating oil off the walls. Reduced combustion chamber and spark plug deposits compared with conventional leaded petrol is another claimed advantage.

The spark plug, however, is a classic case of where the advantages and disadvantages can cancel one another out. Although the deposits may be reduced, the spark plug life may not necessarily be increased as the more severe cold starting requirements (from an electrical point of view) can often increase spark plug erosion especially if the ignition system is uprated.

A further major advantage claimed for lpg is that it extends the effective life of the lube oil by reducing contamination and dilution by fuel.

The major disadvantages to engine durability which has caused problems in the past is high valve-seat wear. Lead compounds in petrol act as lubricants for the exhaust valve seats and some engines — notably those with cast iron seats — encounter rapid seat wear when using lpg (or any other nonleaded fuel) under continuous high-speed driving conditions.

Thus engines intended for lpg use should be fitted with hardened valve seats inserts. Ford is one manufacturer which realising the potential of the lpg sector, has issued a special cylinder head for the Transit with such a seat modification.

The main item of interest to operators when considering lpg is that of fuel cost. Currently the duty on gas is about half that of petrol and the proportion has been maintained throughout the "adjustments" made by various Chancellors.

Solex agrees with the other companies involved in the lpg market that the cost figures do not make a great deal of sense to anyone who buys fuel at top pump price. As with most things it is far cheaper to buy in bulk. With lpg, however, this means investing in a pressure storage tank which effectively means that lpg is for fleet use only.

Al Lighton suggests that a minimum fleet size of 10 vehicles is needed before there is sufficient cost justification for the operator's own tank installation. For a throughput of about 7,000 gallons of lpg a year, the bulk price currently averages about 93p per gallon. Comparing this with a current petrol price of £1.62 or £1.40 less vat then the potential savings are easy to see. However, "potential" is the important word here. It is not quite that simple.

The average cost of a conversion to enable a vehicle to run on lpg is £350. Before any overall benefits can be accrued, this initial first cost must be balanced and this depends to a large extent on the fuel consumption. As an example, a Transit doing about 20mpg on petrol would probably average about 16.6 lit/100km (17mpg) on gas. Using the figures mentioned earlier, this would give a pay back at around 36,530km (22,700 miles).

With the current situation, Al Lighton accepts that there are three operational disadvantages associated with using lpg. These are: (a) the difficulty in gettin gas around the country (a prot lem eliminated with bulk storag if the vehicle always returns t base); (b) the first-cost penalty and (c) the extra space require for the lpg tank.

The first-cost penalty can b eliminated very quickly with th higher mileage vehicle but it i worth remembering that there i nothing to stop the operatc having the gas equipment rE moved and refitted to a rim vehicle when the original vehicl is sold or pensioned off.

Point (c) can be a probler with some private cars but i rarely insoluble in the case of commercial vehicle.

The present levelling off in pc trol prices at the pump ha caused most companies t revise their forecasts on lp usage. Last year it was suc gested that lpg consumption i the UK would rise from a currer annual 35,000 tonnes to aroun 250,000 tonnes by the mit 1980s. Now this predicition ha been reduced to 150,000 tonne over the same period. As A Lighton put it: "It's more pess mistic but still reasonable i terms of growth."

So far as the future is cor cerned, Solex is developing a injection system for lpg whic will be suitable for dual or mon fuel applications. This is m pected to be released in late '83 Conversion of a diesel engin to run on lpg alone is a fainl complicated business. In add tion to the fuel system, the 'Rim tion equipment needs to be ri placed by an ignition system an the compression ratio woul need to be reduced considerabl either by a change of pistons c cylinder head.

Although all this is possible is a fairly drastic move, and s most people who are runnin I pg engines in heavy lorries c buses are using conversions t existing large capacity petrol et gines, eg the Rolls-Royce BE eight-cylinder unit in a Scottis Road Services Leyland Clyde: dale or the Chrysler V8 engin for the Dodge Commando.

The topic of safety is ofte raised by people new to the fu' mainly because the gas is store under pressure in the vehicle. I fact it is claimed that automoth, lpg has proved to be as safe t use, distribute and handle as pi trol.

It certainly has an excellei safety record in countries III.

Holland, the USA and Japa where it is marketed far am widely than in the UK. In „Papa for example, lpg sales are no' running at over two millic tonnes a year, principally for ut in taxis.


Locations: Abu Dhabi

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