AUTOMOTIVE LUBRICANT CHANGES REFLEC1
APICG-4 The World's
First Diesel Engine Oil Category
for Use with Low-Sulphur Fuel
In today's' environmentally conscious society, the diesel engine was initially regarded as being environmentally superior to the gasoline engine. Not only was it more fuel -efficient, but the exhaust emissions were substantially lower in carbon monoxide, hydrocarbons, carbon dioxide, nitrogen oxides, etc. The introduction of catalytic convertors for gasoline-powered vehicles reduced or even reversed the relative merits of the two types of engine, but even so the diesel engine has always suffered from a substantial disadvantage in terms of emissions of particulate material and sulphur dioxide. These two emissions are materially reduced by reducing the sulphur content of diesel fuel. The reduction in the level of sulphur dioxide is directly related to the sulphur content in the fuel, but the reduction in particulates is less obviously directly linked. Of the three primary fuel factors affecting particulate emission, i.e . volatility, aromatic content and sulphur content, the latter is the most dominant because of the effect upon sulphate emissions. Diesel exhaust particulates contain high levels of sulphate, and a reduction in fuel oil sulphur results in a direct reduction in particulate emissions. A further major benefit is that diesel exhaust oxidation catalysts can be fitted to engines operating on low-sulphur fuel, which improves emissions quality even further. Sulphur contents of diesel fuels are therefore being progressively reduced in stages in order to meet the requirements for levels of controlled emissions of on-highway vehicles. America has led the way, with reductions from 0.25% max. to 0.05% in 1993. Europe reduced from 0.3% to 0.2% in 1994, with a further reduction to 0.05% planned for 1996. Obviously, such changes in the fuel composition and emissions legislation are not without relevance to the crankcase lubricant, especially in the important areas of oil consumption and deposit control. The staged reductions in
The Perkins Eagle 2000 series.
regulated emissions have resulted in concurrent improve- ments in engine oil qualities; the development process for the API CG-4 category is described as an
example.
In the US, the requirement for a new heavy-duty diesel crankcase lubricant beyond API CF-4 was identified by an SAE task force; the new category being required by January 1994. In 1991, a team consisting of representatives from the engine manufacturers, oil companies and additive suppliers,HDEOCP (Heavy Duty Engine Oil Classification Panel), met and initially defined the requirements for engine and bench tests, the setting of test limits, the identification
of reference fuel and lubricants, the correlation of field data with engine tests and finally the research reports on each test as required by the ASTM standard process. The category was then agreed to by the relevant ASTM committees. It was realised early in the development process that there was insufficient time or resources available to develop new test procedures, so existing test procedures were used where considered appropriate. The greatest concerns were in the compliance with the emission standards for particulates and nitrogen oxides, both of which are influenced by oil consumption and wear. The main require- ments of the new lubricant were therefore: 1. Minimisation of piston deposits when using low-sulphur fuel (formation of deposits are directly linked to increases in oil consumption)
2. Minimise soot abrasive wear in the valve train (in order to maintain correct fuel-injection and valve-timing), and
3. Minimise increases in oil viscosity caused by soot formation. Compatibility with particulate traps and catalysts was not a consideration, since none of the engine manufacturers of heavy-duty diesels were using after-treatment systems to meet the 1994 emission requirements. Also, the existing API CF-4/SG and API CF-4/SH were already satisfactory in this respect for light-duty high- speed diesels. Sub-groups were then formed to examine each individual test requirement area in detail, namely tests for piston deposit and oil consumption control, soot abrasive wear, viscosity, filter plugging, oxidation, corrosion, foaming and finally shear stability. The API CG-4 specification was then incorporated into the Chemical Manufacturers Association Code of Practice, this now being an integral part of the API Engine Oil Licensing and Certification System currently used for passenger car motor oils, i.e. API SH. The Code ensures that the lubricant meets the performance requirements by stipulating suitably rigorous procedures for testing and record keeping. After the ASTM had completed their work in establishing all the requirements for this new category, there followed a one-year delay before licenses were granted in order to allow sufficient time for the additive manufacturers to complete their test programmes, base oils to be tested and read-across criteria to be developed. The HDEOCP development Committee is now working on a new category PC-7 for 1998 USA diesel engines designed to meet the 1998 emission requirements. For readers requiring further detail, the developments briefly referred to above are covered in greater detail in the Society of Automotive Engineers Technical Paper Series No. 941939
(Continued/P7)
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