1 / 9

Measuring Engine Performance

Measuring Engine Performance. ME 115 Laboratory Spring 2008. Otto Cycle Review. Cengel & Boles, Thermodynamics: An Engineering Approach, 2006. Common terms used to compare engine performance. Brake power (bp): net power output of an IC engine Torque: A force acting through a radius

sheila-bentley
Télécharger la présentation

Measuring Engine Performance

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measuring Engine Performance ME 115 Laboratory Spring 2008

  2. Otto Cycle Review Cengel & Boles, Thermodynamics: An Engineering Approach, 2006.

  3. Common terms used to compare engine performance • Brake power (bp): net power output of an IC engine • Torque: A force acting through a radius • RPM: engine speed, in rotations per minute • Specific fuel consumption (sfc): rate of fuel consumption per unit of brake power

  4. Mean Effective Pressure • MEP: a fictitious pressure that, if acted on the piston during the entire power stroke, would produce the same amount of net work as that produced during the actual cycle (Cengel & Boles, 2006) • If the MEP goes up, the cylinder volume can go down and still achieve the same power output

  5. Mean Effective Pressure, cont. • Indicated MEP (imep): uses the total power output minus the power needed for the intake and exhaust stokes (indicated power) • Brake MEP (bmep): the power used to overcome friction in the cylinder is also subtracted; this term is used more often than the imep

  6. Brake Thermal Efficiency • Brake thermal efficiency: brake power/rate of heat output for complete combustion • Brake thermal efficiency=indicated thermal efficiency* mechanical efficiency • Mechanical efficiency: related to the amount of power used to overcome friction

  7. Carnot Efficiency • To see how well our engine is doing, we can compare our brake thermal efficiency to the Carnot efficiency • Remember that the Carnot efficiency is the best we can do! • h=1-(Tlow/Thigh), where T’s are in absolute scale • We could estimate Thigh as our exhaust temperature • Tlow is our ambient temperature

  8. Engine Irreversibilities • Heat transfer from the cylinder wall during compression: will this irreversibility be larger for slow or fast engine speeds? • Pressure losses across the valves: will this irreversibility be larger for slow or fast engine speeds? • Frictional work due to sliding ring seals and other rotating components: will this irreversibility be larger for slow or fast engine speeds?

  9. Energy Efficiency Variation with Engine Speed Decher, 1994, Energy Conversion: Systems, Flow Physics and Engineering.

More Related