Evaluating the Soot Handling Performance of Diesel Engine Oils through Optimized Engine Testing Protocol

Majority of light and heavy duty commercial vehicles on road in India use API-CF grade lubricants. Soot accumulation in lubricating oil can result in engine wear and lubricant’s viscosity increase thereby affecting its pumping ability and drain interval. Due to faster lubricant degradation and with emergence of newer engine technologies, there is increasing demand of improving performance of lubricants particularly with respect to soot dispersancy. This paper describes the various engine hardware modifications and optimizations carried out on a commercial BS II, 4-cylinder turbocharged diesel engine in order to develop a flexible engine test procedure for evaluating the lubricant’s dispersancy/anti wear characteristics up to 6% soot levels. The test severity was generated in order to match real time environment by incorporating various engine hardware modifications like inlet air restriction, retarded injection timing, increased fuel delivery, auxiliary oil sump unit, and reduction in injector pressures. The soot levels generated at the end of the test were correlated to the FSN values. Oil samples were drawn at the end of every 25 hrs of engine operation and analyzed for soot in oil & wear metals using TGA (Thermo gravimetric analysis) & ICAP (Inductively Coupled Argon plasma) spectrometer respectively. Subsequent to the establishment of the test procedure, four test oils were evaluated for soot levels varying from 2 to 6 %. A correlation analysis was conducted to ascertain the dependence of wear on viscosity change and soot percentage. The test procedure is found to be capable of differentiating the performance of candidate oils with respect to their soot dispersancy and wear characteristics. Owing to the flexibility of the test procedure for simulating varying soot levels, it can be utilized for development of lubricants catering to different performance levels.