Combustions Final Flashcards
Using exhaust gas recirculation (EGR) can increase combustion efficiency by allowing higher maximum in-cylinder temperature using low heat capacity gases.
False
Variable geometry turbocharger enables maintaining the maximum efficiency of turbocharger
by changing vane angle depending on the engine speed.
True
Gasoline direct injection (GDI) engine has higher efficiency than port fuel injection (PFI) engine
thanks to __________ effect that lowers knocking tendency that enables higher compression ratio.
Charge Cooling
Which statement is false regarding downsized engines?
They have better noise and vibration characteristics.
Which statement is false regarding homogeneous charge compression ignition (HCCI) engine?
Inhomogeneous air-fuel mixture and high portion of diffusion flame.
What is the main purpose of late post injection (after end of combustion) in diesel engines?
To activate after-treatment system by increasing exhaust temperature.
Which statement is false regarding Methanol as an alternative fuel for SI engines
It has higher heating value than gasoline.
Application of biodiesel can decrease pollutant emissions since it is _________ fuel so it can
promote complete combustion.
Oxygenated
Which statement is false regarding series type hybrid vehicles?
They can deliver power to wheel directly using ICE
Full hybrid type usually has longer mileage than micro/mild type hybrid vehicles by allowing
external charging.
False
Compared to internal combustion engines, the external combustion engines have quicker and more accurate control on engine load and speed thanks to their simple structure and flexibility on fuel type
False
Internal Energy is a _____ function and heat (or work) is a ___ function.
point/path
How many crank angle degrees are required to complete an engine cycle for 2-stroke engine?
360
Which of the following statements regarding thermodynamics is false?
in ideal gas equation. pressure is inversely proportional to temperature.
Which of the following statements holds true for the ideal Otto Cycle (Theoretical) during combustion?
constant volume
Heat is transferred to a heat engine from a furnace at a rate of 80 MW. If the rate of waste heat rejection to a nearby river is 50 MW, determine the thermal efficiency for this heat engine.
37.5%
Which of the following statements regarding gasoline/diesel engines holds true?
conventional diesel combustion is governed by diffusion flame (heterogeneous combustion)
Compared to internal combustion engines, external combustion engines generally have higher thermal efficiency because of much simpler engine structure and less requirement for cooling.
False
Four stroke engine has constant rotational force because work is produced in every rotation.
False
The stoichiometric/theoretical air is the exact quantity of air necessary to provide enough oxygen for complete combustion.
True
The engine size normalized work per cycle divided by the volume displaced per cycle is the:
mean effective pressure
(In four-stroke engine) when the piston reaches bottom dead center (BDC), the intake valve closes and the piston travels back to top dead center (TDC) with all the valves closed is the ____ stroke.
CompressionW
What is the thermal efficiency of an air-standard otto cycle operating with a compression ratio (r) of 10:1? Use ration of specific heats k=1.4
60.1%
