FAST - Engine friction prediction
Rapid FMEP prediction for complete engine friction assessment
FAST provides a practical way to predict mechanical friction across the complete engine. It calculates Friction Mean Effective Pressure (FMEP), the theoretical mean effective pressure required to overcome engine friction, and reports the contribution of the key systems that make up total engine friction.
The tool is designed for use early in development, when only limited design information may be available, but engineers still need a reliable view of likely friction losses. FAST uses a mixture of empirical and semi-empirical formulae, with separate calculations for each engine subsystem, making it more predictive than simple correlation-based approaches while remaining much faster than detailed CAE.
What FAST predicts
FAST includes empirical models for the main contributors to engine friction, including:
- Piston rings and piston skirt
- Main bearings and big end bearings
- Valvetrain
- Timing drive
- Crankshaft seals
- Crankshaft windage
- Oil pump, water pump and other driven auxiliaries
- FEAD belt losses
- Crankcase pumping losses for applicable wet sump engines
Use FAST to predict mechanical friction earlier, understand engine loss contributors faster and make better-informed decisions before committing to hardware or detailed CAE.
Piston ring and skirt
FAST calculates piston ring and skirt friction across the crank angle using the relationship between contact force, sliding speed and friction coefficient. For piston rings, the model accounts for ring tension and, under fired conditions, the effect of cylinder pressure on the top and second rings. For piston skirt friction, the model accounts for inertial effects under motored conditions and gas force effects under fired conditions. The friction coefficient is calculated from sliding speed, force and oil viscosity using a Stribeck-type relationship.
Valvetrain, timing drive and bearings
FAST uses semi-empirical formulae for valvetrain and timing drive friction. Valvetrain calculations reflect the valvetrain type, cam-follower contact type, camshaft arrangement and lash adjustment approach, while timing drive calculations account for drive type and layout. Bearing losses can be calculated using simplified equations, while more detailed bearing analysis can be introduced if required.
Seals, windage, pumps and FEAD
FAST accounts for friction and parasitic losses that are often missed by component-level analyses. These include crankshaft seal loss, crankshaft windage, oil pump and water pump drive power, unloaded alternator and Air-Conditioner (A/C) losses, and FEAD belt friction. This gives a more complete prediction of whole-engine mechanical friction.
Typical uses
FAST supports engineering tasks such as:
- Comparing alternative engine architectures at feasibility and concept stage
- Setting friction targets for new engine development
- Interpreting motored friction teardown test results
- Evaluating claims for friction reduction measures
- Understanding the friction impact of downsizing and rightsizing concepts
- Identifying the main contributors to friction in production engines
Why it matters
Mechanical friction is difficult to calculate with high accuracy under realistic operating conditions, and physical test methods can be expensive, time-consuming and uncertain. FAST gives engineers a rapid predictive view of friction behaviour, helping them focus development effort on the systems with the greatest impact.
Use FAST to predict complete engine friction, understand subsystem contributors and make earlier decisions on low-friction engine design.