Discussion Overview
The discussion revolves around the measurement of friction power using an electric dynamometer during motoring tests of engines. Participants explore the relationship between engine output power, friction power, and the role of the dynamometer in these measurements.
Discussion Character
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- Some participants explain that during a motoring test, the engine's power is absorbed by the dynamometer, and when the fuel supply is cut off, the dynamometer acts as a motor to maintain engine speed, which allows for the measurement of friction power.
- There is a question regarding whether the power supplied to the motor should equal the engine's output power to overcome friction and maintain speed, indicating confusion about the relationship between these powers.
- One participant clarifies that when an engine is idling, the power output is zero, and thus all fuel energy is used to combat friction power, suggesting that the energy required by an external motor to maintain rpm equals the friction power.
- Another participant confirms that friction power does vary with rpm, noting that friction mean effective pressure (FMEP) is proportional to mean piston speed, which is linked to rpm.
- It is mentioned that to calculate friction power, FMEP must be multiplied by volumetric flow rate, which also varies with rpm, indicating a relationship between friction power and the square of rpm.
Areas of Agreement / Disagreement
Participants express some agreement on the concept that friction power can be measured through the dynamometer setup, but there remains confusion and differing interpretations regarding the relationship between engine output power and friction power, as well as the implications of rpm on friction power.
Contextual Notes
Some assumptions about the conditions under which the measurements are taken, such as the engine being idling or under load, are not fully explored. The discussion also does not resolve the confusion regarding the equivalence of power supply to the motor and engine output power.