Communication gap barrier to mastering petrol differences

Press, 28 January 1988, Page 28

Communication gap barrier to mastering petrol differences

The introduction of unleaded petrol in New Zealand has been greeted with passive resistance by the majority of motorists. The motoring public’s disinterest probably stems from the implications of commentators that unleaded fuel can cause engine damage to cars, or at least cause a decline in performance and an increase in petrol consumption. Such implications have no foundation in fact, according to the principal engineer of the New South Wales Pollution Control Commission, Mike Mowle, who participated in a series of seminars on unleaded petrol, conducted by the Ministry for the Environment. Mr Mowle’s case for unleaded petrol was outlined in the December issue of “Radiator,” the official journal of the Motor Trade Association. Outlining the beginnings of lead in petrol, he said that it had been added as long as 50 to 60 years ago when it was discovered that tetraethyl lead or tetramethyl lead had the effect of increasing the fuel octane number. It was also subsequently discovered that the presence of lead in petrol caused considerable deposits to build up in the combustion chamber and on spark plugs, and if allowed to build up indefinitely these deposits would eventually cause engine failure. Consequently, scavengers — ethylene dichloride and ethylene dibromide — were added to the leaded petrol to remove the deposits. However, the combustion products of the scavengers, including hydrochloric - and hydrobromic acids, are highly corrosive and remove the lead from the combustion chamber. Lead and scavengers have adverse effects on engines, including deposits on valves and plugs, deterioration of engine oil and increased engine wear, as well as corrosion of exhaust systems. New Zealand’s unleaded petrol has a Research Octane Number of 91 and a Motor Octane Number of 82 minimum, according to Mr Mowle.

However, there is a body of opinion in this

country that believes the 1 more important Motor Octane Number is not constant because the Marsden Point refinery would have to use an uneconomic amount of crude to produce either unleaded or leaded petrol of the claimed octane numbers. It is this body of opinion that, to a large extent, raised concerns about the compatibility of New Zealand petrol in some imported cars, although suspicions have been voiced about the additives used in some brands of petrol. The octane requirement of an engine depends primarily on its design, compression ratio, combustion chamber geometry, inlet and exhaust valve configuration and ignition characteristics. Octane requirement is affected by engine condition and adjustments, ambient and operating conditions. When an engine’s octane requirement is not satisfied by the fuel, which means that it has too low an octane, knocking or pinging will be experienced. Slight knocking is not detrimental and, in fact, many engines achieve their maximum economy in this condition, Mr Mowle claims. Low speed knocking caused by petrol with too low a Research Octane Number will rarely cause engine damage, even when it is severe. However, high speed knock, which occurs when the Motor Octane Number is too low, can cause damage, if it is severe. This damage would generally take the form of a burned or failed piston

BEHIND the WHEEL with Peter Greenstade and, in extreme cases, total engine failure. Engines which have a very low octane demand because of their design will operate satisfactorily on 91 Research Octane Number unleaded petrol without any knocking. Use of 96 octane in such engines will provide no benefits. Under high speed/high load conditions, thermal and mechanical stresses on the valve and its seat are high and this can lead to valve recession. If the valve seat material is soft, as is likely in older engines with cast iron cylinder heads, valve recession can occur. Lead deposited by leaded petrol on the valve seat affords protection and reduces recession to within designed limits, but very little lead is needed to provide such protection. In the last couple of decades or so, most vehicle manufacturers have hardened valve seats to prevent excessive valve seat wear.

Under the circumstances, valve seat recession should not be a significant problem with unleaded petrol, but motorists with older engines should exercise some caution by prudently running their cars on a tank full of leaded, petrol on a ratio of one-in-five up to one-in-ten of unleaded. Actually, the amount of petrol is unimportant, but some leaded petrol should be used at regular intervals. It is worth noting that in January, the United States Environment Protection Agency imposed a complete ban on lead in petrol. Valve failure caused by lead and scavengers is a much more likely occurrence in engines running on leaded petrol than valve seat recession is in engines running on unleaded petrol, said Mr Mowle. Modern engine oils include additives which are designed to reduce the deteriorating effects on the oil of blow-by gases, which include fuel, air, combustion products, including water, and if leaded petrol is used, lead and combustion products of lead and scavengers. Oil additives are used up three times as fast with leaded petrol, thus engine oil should last three times as long if unleaded petrol is used. Engine rusting is also a significant problem with leaded petrol, but a minor problem at most with unleaded petrol, because the anti-rust additives in engine oils are used up by water and also by the acids in the blow-by gases when leaded petrol is used.

Studies in the United States show engine wear rates are two or three times greater when leaded petrol is used, due to corrosion in cold temperatures. In a cool climate, a typical engine running on leaded petrol would have substantial piston ring and cylinder bore wear after 150,000-200,000 kilometres, whereas use of unleaded petrol would substantially extend useful engine life. By the same token, with leaded petrol use, fouling and chemical corrosion of spark plug electrodes occurs quite quickly, typical spark plug life being 10,000-15,000 kilometres. There is no fouling with unleaded petrol when plug life should be extended to 30,000-100,000 kilometres. Similarly, exhaust corrosion is accelerated by use of leaded petrol. The lead scavengers combust to form acids which increase the pH level of exhaust gases to within the range of 2 and 2.6. That compares with exhaust gases from an unleaded petrol engine which range from 3.5 to 4.2. This pH difference accounts for the additional corrosion, Mr Mowle concludes after citing some comparative tests conducted in Australia and the United States. Whether the evangelistic claims of such experts as Mr Mowle will move the New Zealand motoring public remains to be seen. Certainly, so long as doubts remain in the minds of the public regarding the claimed efficiency of New Zealandrefined petrol, and confusion exists over the merits of various oil companies’ additives, the greater New Zealand motoring public is unlikely to concern itself about the pros and cons of unleaded petrol. It has been listlessly promoted on the so-called benefits that might accrue from keeping New Zealand’s air undefiled by lead, which is a proposition with which many New Zealanders at present appear to be unconcerned. Could it be that New Zealand’s big problem concerning petrol boils down to communication, or the lack of it?