Thermodynamic engine cycles Flashcards
What are the two types of recipicating engine cycles
Otto: spark ignition
Diesel: Compression igntion
What is specific heat
Energy required to rase mass by 1 Kelvin
What is a thermocouple
Used to measure temp in cylinder
What is the working fluid
Gas that does the work (so air)
What is U
Internal energy- Will change with work or heat
What is an adiabatic process
No exchange in heat or mass
What is STP
Standard temperature and pressure. Defoult is 20 degrees and 1bar
What is isentorpic?
No entropychange
What is cylinder displacement
Area of cylinder * stroke of cylinder
What is compression ratio?
Volume at TDC divided by volume at BDC
Describe the 4 tropic stages of ideal otto cycle
Se fig 8
What is the definition of thermal efficiency
Work out divided by heat in.
-note that thermal eff can be expressed with compression rario when assuming the otto cycle have isentropic compression and expantion, meening that the compression ratio effect eff
What is the ideal compression ratio for real otto cycle, and why?
7-10 is ideal:
If we do a higher compression ratio, we risk auto-ignition, uncontrolled combustion, knocking
Describe the 4 tropic stages of ideal diesel cycle
Se fig 9
What is the visual relation between otto and diesel cycle? And how does this effect the efficiency of diesel compared to otto?
Diesel cycle is otto cycle just cutting the top. This is called cut-of ratio. As this cup-of makes the W-out smaller and hence reduce thermal efficency, Otto cycle is in theory more efficient. This is not the case in reality.
Why does CI engines in reality have a higher efficiency?
As the diesel cycle can have a higher compression ratio without the negative sideeffect that otto cycle have, diesel cycle has in practicality higher thermal eff, as compression ratio has a large effect of eff
