J. FUTURE WORK OF CIMAC "LUBRICANT" WORKING GROUP
The actual task of this working group in issuing the above mentioned 5 bulletins is well under way and is expected to be completed end mid year 2001. The working group has now started considering its future work. Everything is still open and no direction or decision has yet been made on the future work of this WG. Nevertheless several areas of studies have already been proposed and one potential area is to study the impact/demands of environmental control measures / engine designs on the lubricant. It is obvious that future lubricant development have to follow the requirement of diesel engine development; emission regulation issues/measures have introduced an additional factor for consideration in the development of future lubricant.
IMO and international bodies are all looking at strict emission rules and limits on several points such as:
・ NOx
・ SOx
・ particulates
・ CO
・ HC
Relevant to the lubricating oil, potentially three of the above have or will have an influence on oil technologies: SOx, NOx and particulates.
a) SOx
There is a trend to reduce the SOx emissions. This can be done mainly by operating on low sulphur fuel. As a consequence the corrosive wear will be lower and then the BN required has to be lower. On the other hand as the fuel will still be heavy fuel oil there will still be a need of detergency/dispersency. In a typical current lubricant, the BN and detergency are closely related - i.e. the additive that provides the BN also brings along it the detergency. So if we keep the same typical current chemistry, either i) the detergency will be too low if the lube oil is adapted (lowered) in BN to meet the low sulphur fuel - and this may result in engine fouling or ii) the BN will be too high if lube oil is adapted to HFO operation detergency requirement.
This new approach of low sulphur heavy fuel will need a complete reformulation of lube oil chemistry which involve new R&D, testing of new products for such heavy fuel.
b) NOx
For the time being, there are several ways to reduce the NOx emission of diesel engines.
1) Engine adjustment - Various adjustment - eg injection rate, injection timing, combustion process - allows the engine Nox emission to be significantly reduced. This has no real major influence on lube oil.
2) Additional treatment (before or after the engine)
i) Water injection. It can be done through various ways such as:
・ water in fuel emulsion,
・ direct injection in the chamber of combustion through separate injector,
・ injection through the scavenging air via a humidifier. In that process the air for combustion is saturated with water before entering the engine.
There is, in view of large quantity of water injected in the engine, a risk of water introduction into lubricating oil. This means that either i) the oil has to tolerate a higher water content than now - without any detrimental effects to its properties, as well as its lubrication of the engine (for information water content general alarm limit is set at 0.2 % and rejecting limit at 0.5 %), or ii) that in case of water introduction/contamination it must be able to release high amount of water (eg in the purifier) without any adverse consequence to its chemisty.
ii) Post treatment like SRC (Selective Catalyst Reactor). Such post treatments are very efficient and are now quite common. But special care has to be taken on the choice of SCR or oil because some catalyst used in SCR can be poisoned by some chemical additive of the lubricant.
This again poses a new challenge for the oil maker, i.e. to develop oils that have minimal adverse impact on any "after treatment" equipment such as SCR.
c) Particulates
There are particulates in the exhaust gas that may have to be controlled - these are soots, unburnt particules, ashes etc. An important part of those particulates are the ashes of the lubricating oil additive.
As an example, a 50 BN oil typically has 6 to 7% sulfated ash. Specific lubricating oil consumption is about 0.5% of fuel consumption. If for example the fuel ash is 0.1% as bunkered represents about 0.03% at engine inlet, a simple estimate would suggest that the ashes found in exhaust are 1/2 due to HFO, and 1/2 due to oil. So it is obvious that one of the options to reduce particulate emissions is to reduce the ash level of lubricating oil additives.
But there is a conflicting point between a) having a high detergency, dispersency and BN which necessitate high concentration of additive, and hence high ash level (based on existing chemistry) and b) the future requirement of low ash oil in the aim of lowering particulates emission of HF marine diesel engines.
This new requirement will challenge the oil companies to develop new chemistry and diesel engine manufacturer to reduce lube oil consumption. In fact this reduction is already in progress; 10 to 20 years ago the SLOC was at around 1.3 to 1.5 g/kW.h. but today oil consumption has been reduced, and it is not uncommon to see SLOC as low as 0.3-0.4 g/kW.h.
