Characteristic of combustion in SI-engines Flashcards
Does diesel engines operate at fuel rich or fuel lean?
lean
Does otto cycle operate at fuel rich or lean?
Fuel rich
What is equivalence ratio=1 called
homogenius
How is fuel injected in to SI engines?
injection or by carburettor
What is port fuel injection and what is its relation to gasoline?
With port fuel injection, gasoline is sprayed into the intake manifold, where it mixes with air, and then is sucked down into the cylinders. Direct injection places an injector on each cylinder, spraying gasoline into the cylinder itself.
- The difution of fuel to gas (gasoline) is why otto cycle is a bit unpopular. The gasoline is to volatile for temperature changes , weather, pressure and so on
What is the reaction zone?
Reaction zone is where the chemical reaction in the SI engine occur.
What is the post-flame zone
What lies behind reaction zone in SI combustion
What is pre-flame?
The zone in front of the reaction zone in si engine
What is moving flame front
The direction of the reaction zone
What is 1D laminar flame propagation?
It’s a simplified theoretical model used to study how a flame moves through a premixed fuel-air mixture, in a controlled, idealized way.
Why is turbulant pre-mixing important in SI engines?
air-flow need to be turbulent to have enough speed to fill the whole chamber before the intake closes (yes ola, turbulent is actually quicker then laminar)
Just a note to myself that there is different scales for turbulence, depending on the length of eddies
Se pp 9, slide 12
Mention three turbulent regimes
Wrinkled laminar flame, flamelets in eddies and distributed reaction.
- its basically three different sizes of eddies creating different behavior of flame on the lager scale
What is eddies
An eddy is a movement of fluid that deviates from the general flow of the fluid. An example for an eddy is a vortex which produces such deviation
What is the relation between equivalence ratio and minimum ignition energy?
With a equivalence ratio higher then 1.5, it takes quite a lot of energy to ignite gasoline. On the other side, a to low equivalence ratio also leads to the need for high equivalence ratio
where do we want pressure max to occur at for SI engines
TDC
what is flame developement angle, rapid burning angle and overall burning angle in SI engines
the relation between mass fraction burned and CAD. For the flame developement angles the flame is quite slow before it for the angles in rapid burning angle burnes quite fast. The combination of the two parts in overall burning angle. Says a lot about knocking and shit like that
what is knocking?
Knocking comes from auto-ignition before flame front comes in the unburnt zone.
