Exercise 3 and 4 Flashcards
Solve exercise 3 task 1,a,b,c,d for eq.ratios and all that
Why do we ignore spear fuel for stoiciometric calculations?
Assume ideal reaction
Why is ideal cycle so different from real cycle?
Ideal cycle contains a lot of simplifications and assumptions that daddy diesel made when he first designed the diesel motor
what is Indicated thermal efficiency for an engine?
Indicated thermal efficiency (often written ηth,iηth,i) is a measure of how efficiently an engine converts the chemical energy of the fuel into indicated work
What is cutoff ratio?
volume at the end of combustion (before expansion)
divided by
volume at the start of combustion (after compression).
A higher cutoff ratio means the fuel burns over a longer piston stroke → more heat addition → higher efficiency loss (more heat at lower pressures).
A lower cutoff ratio generally means more efficient combustion, but it must still be enough to fully burn the injected fuel.
Some engines have two spark plugs If everything else is kept the same, list three
advantages and three disadvantages this gives for modern engine operation and design.
Advantages:
- Shorter flame travel distance – closer to constant volume combustion. Results in
higher real thermal efficiency
- Less chance of knocking
- Less chance of poor ignition (and misfire)
Disadvantages:
-Difficult to fit valves and spark plugs into combustion chamber
- Higher cost
- Need for more complex ignition system
What are the two things that the most effect flame speed?
-Wheter the flame is turbulent or laminar
-where in the cycle the flame is described
Does laminar flames in combustion chambers exist?
No. they are just theoretical. In reality flames are more tubulent and result which result in lower flame propagation
