Time to lower the viscosity of lubricating oils to boost efficiency?

The continued market demand to have more efficient machines, thus achieving energy savings and emission reductions, has motivated manufacturers to look for improvements even in area that have never been explored and evaluated till now. A paper, “Development, testing and qualification of innovative low viscosity oil in turbomachinery applications” presented by Lorenzo Naldi and Massimo Camatti of Baker Hughes, a GE company, and Manuela Toscanini and Marco Lattuada of Eni SpA- Research & Technological Innovation Department at the 2018 Asia Turbomachinery Symposium says that a new turbine oil with lower viscosity than that of typical turbomachinery lubricants can deliver energy savings.

For many years, the viscosity of lubricating oil for industrial turbomachinery application has been a pre-determined parameter and basically an industry standard set on two reference values: 32cSt and 46CSt at 40 deg. C. Keeping oil viscosity unchanged, OEMs have been developing their products and technologies achieving significant improvements in terms of machinery performance and power density. Oil companies at the same time have made available improved quality lubrication products with enhanced properties as far as concern aging resistance and anti-wear characteristics.

The authors of the paper’s companies started in 2010 to brainstorm about the opportunity to join their respective competencies and efforts to develop an innovative oil which could contribute to enhance the turbomachinery technology and related industry. After extensive discussions which evaluated several potential areas of work, a decision was taken to approach the study of a low viscosity oil (15-22 CSt. @ 40 deg. C) having in mind the following potential target benefits:

• Increase the overall machinery efficiency by reducing the mechanical viscous losses and relevant heat generation

• Improve bearings lubrication behavior and minimize pad temperature at very high shaft sliding speed of advanced highperformance turbomachinery

• Reduce the oil flow requirement and optimize design of lube oil systems

Among several oil candidates formulated for the scope, two low viscosity oils, viscosity grade (VG) 15 and VG 22, were developed for laboratory evaluation. Based on predicted bearing dynamic coefficients with selected oil viscosities, rotordynamic analysis of several turbomachinery models were performed showing limited impact with respect to conventional oil viscosity.

The new product, characterized by a 15cSt viscosity grade, has been subjected to a wide range of tests to evaluate its characteristics and impact on turbomachinery performance: validation was initiated with laboratory tests and proceeded by running representative models of the turbomachinery families under typical operating conditions.

The authors of the paper report proven reduction of mechanical viscous losses of lubricated rotating parts in a range of 5-15%, with respect to a standard ISO VG 32 oil; smooth running behaviour and operating parameters of machinery and related auxiliary equipment in line with those recorded with a standard ISO VG 32 oil.