Friction losses inside an engine necessarily damage fuel consumption. Some of the power which would otherwise feed through to the transmission and ultimately to the wheels must be sacrificed in overcoming the resistance of moving parts, in bearings and at the cylinder walls. Part of that resistance is ‘hydraulic’. The film of lubricating oil, which separates relatively moving surfaces in order to minimise metal-to-metal contact and resulting wear, nevertheless creates its own impediment to free movement.
That hydraulic resistance is largely a matter of viscosity, a measure of the lube oil’s thickness. For many years, viscosity was virtually the only consideration. If you moved to a thicker lubricant, both oil consumption and component wear would be reduced. On the debit side, frictional losses and therefore fuel usage were increased. But, back then, that was not a critical concern.
Infineum, the additive maker owned jointly by Exxon and Shell, has embarked on an ongoing innovative wear study programme, using what it calls ‘advanced radioactive tracer technology’.
When fuel costs started to rise in the 1970s, the effect of internal engine friction on consumption came into sharper focus. That was when additive specialists such as Lubrizol intensified their researches, one vital challenge being to reduce lube oil viscosity without jeopardising wear-related engine durability. Part of the challenge was, in simple terms, to formulate oils which were thinner than existing grades when cold, but which did not lose their wear-prevention qualities when the engine reached running temperature. In past decades the key additive development was based on zinc dialkyl dithio-phosphate (ZDDP) chemistry.
That additive research is now entering a new era, driven in large part by emissions regulations which, in diesel engines, have seen the widespread adoption of EGR (exhaust gas recirculation) which pushes more soot into the crankcase oil, impairing its lubricity, implying a need for shortened drain periods with attendant service cost increases. As such it has restricted ZDDP applications. Infineum, the additive maker owned jointly by Exxon and Shell, has therefore embarked on an ongoing innovative wear study programme, using what it calls ‘advanced radioactive tracer technology’.
During tests on newly-formulated lower-viscosity oils, it has been possible to measure wear much more accurately than previously, in cylinder liners, piston rings, big-end bearings and fuel injector cam lobes in particular. Those components are ‘labelled’ with radioactive isotopes that act as tracers. A (lead shielded) gamma ray detector in the engine sump monitors, in real time, wear-indicating isotope levels in the oil, while the engine is not only running, but is put through selected load/speed cycles.
Advancing engine technology, notably through the use of newly-developed materials, has brought tremendous improvements in durability over recent decades. Parallel advances in lubricant formulations have played a complementary role.
This ability to obtain wear data accurately without taking the engine apart makes radioactive tracer technology a powerful tool, says Infineum, “for studying the wear responses of multiple engine surfaces simultaneously” and under different operating conditions.
Advancing engine technology, notably through the use of newly-developed materials, has brought tremendous improvements in durability over recent decades. Parallel advances in lubricant formulations have played a complementary role. The latest research techniques developed by Infineum and other additive suppliers promise even greater life expectation from future engines, especially in the heavy-duty sector where cost pressures are forcing truck and bus operators to extend vehicle replacement cycles.
The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.
Alan Bunting has a background in engineering, and has been writing on commercial vehicle and powertrain related topics since the 1960s. He has been an Automotive World contributor since 1996.
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