Study on Fuel Efficiency and Durability Aspect of a Low Viscosity Heavy Duty Diesel Engine Oil

In order to meet Corporate Average Fuel Economy (CAFÉ) regulations and Bharat Stage VI (BS VI) emission regulations, Indian auto original equipment manufacturers (OEMs) are adopting low viscosity engine/axle/transmission oils to achieve overall fuel efficiency gain. Attaining fuel economy by reducing oil viscosity is already established for passenger car motor oils (PCMOs) but is in its initial phase for heavy-duty diesel engine oils (HDDEOs). Now SAE 15W-40 is the most widely used viscosity grade by volume for HDDEO. In India, a large number of old vehicles meeting BS II, BS III and BS IV norms exists and require sustainable strategy to reduce fuel consumption, as well as overall greenhouse gas emissions. In this paper, authors discussed the development of low viscosity heavy duty diesel engine oil in 10W-30 viscometrics meeting API CH4 specification. Fuel economy credential of the developed product was carried out on a chassis dyno w.r.t. the reference oil in “Delhi Bus Driving Cycle (DBDC)”. The authors also studied the effect of viscosity on the engine durability by mileage accumulation test of 40,000 kms run in chassis dynamometer by monitoring engine wear in used oil analysis. Finally to check the fuel economy benefit and oil performance in field, a field trial was conducted on old BS II and BS III buses in two bus depots. Fuel economy (FE) was calculated based on the KPTL (kms per ten lts) value of the candidate oil w.r.t. the reference oil. From the trial data it was established that low viscosity engine oil provides adequate durability with sustained fuel economy. However, the FE has direct bearing on driving conditions and more stop/go condition affects fuel economy benefits.