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ENCYCLOPAEDIC

Refinement of Engine In-Cycle Losses of Parasitic and Errant Dynamic Nature

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Surface Measurements
Ultrasound Measurements
 

The key drivers in engine development are: i) fuel efficiency, ii) emission control and iii) NVH refinement.

 

Reduction of friction contributes directly to (i) whilst it can influence (ii) and (iii) in a contrary manner. Thus it is important to understand the underlaying causes of friction

 

There are indirect and direct measurements of friction: Wear implies excessive friction (indirect assessment).

Lubricant film thickness (thinner films mean increased boundary friction, whilst thicker films entail increased viscous shear)

 

Measuring Friction

  

 

                        

Floating Liner Validation Tests
 

Floating liner results are validated with open cylinder motorised tests 
In this configuration inertial force equates frictional resistance
Inertial force is determined by measurement of liner acceleration relative to the block
 
  • More realistic conditions, including the effect of chamber pressure upon friction is obtained under motored condition with cylinder head in place
  • The Honda CRF 450 engine develops peak chamber pressures of the order of 15-25 Bar according to engine speed under motored condition.
  • This introduces the effect of pressure loading on piston-bore friction without the additional interactions caused by combustion.
 
 

 
  •  Friction follows the same characteristic variations as in a fired engine, except that peak asperity friction occurs at the TDC with the maximum chamber pressure there rather than at a detonation point somewhere beyond it in a fired engine.
  • Peak viscous friction occurs at mid-span.  

 

Experiments are carried out at different levels. At one level measurements are required to provide data for numerical analysis. For example, see below measurement of ring-bore conformance.  Ring-Bore Conformability. Typical bore for motorsport application is measured in-situ using a co-ordinate measuring machine with an accuracy of ±1 µm. The fitted compression ring outside radius is also measured. Good conformability is noted.

 a) Fitted ring and bore

     

 

 

    

 

b) Ring-bore measurement detail

                     

  Validation of numerical predictions are carried out with the help of experiments. These include in-situ film thickness measurement using ultrasonic devices. Also the performance of various  liners with different textures to retain lubricant  during engine operations can be compared. The test rig to conduct these experiments is currently being designed with the aid of CAD and multi-body dynamics as in the example on the above left.