The cold-cranking simulator was designed as a method of determining the low temperature performance of lubricants, in the specific condition of “cold cranking” – i.e. starting a cold engine. In this condition, the only energy available to turn the engine comes from the starter motor and the battery, and it has been widely assumed that the system acts as a constant power viscometer.
This test method covers the laboratory determination of apparent viscosity of engine oils at temperatures between –5 and -35C and at high shear rates. The results are related to engine cranking characteristics of engine oil. A measured amount of sample is subjected to an extreme low temperature for 3 minutes. The rotor spins for 1 minute in the sample and the speed of the rotor is measured by keeping ohms resistance at zero. The speed-reading is used to determine the viscosity on a calibration curve.
Why we need to know:
- Cold-cranking simulator simulates rheological process of “an average engine” during cold starting. The Starter motor was replaced with a small series wound universal motor, a typical sewing machine motor, and the engine, with a specially designed cold cylinder and an insulated cylindrical rotor with a pair of parallel flats.
- he sample oil is continuously sheared under a periodically varying shear rate, lower when the flats pass. Oils in real engines are similarly sheared, high in the journal bearings, oscillatory on piston rings and low in galley. Most developmental work went into proper sizing of the flat to simulate relative shear rate distribution in an “average engine.