Combustions Final

Question 1

Using exhaust gas recirculation (EGR) can increase combustion efficiency by allowing higher maximum in-cylinder temperature using low heat capacity gases.

Answer 1

False

Question 2

Variable geometry turbocharger enables maintaining the maximum efficiency of turbocharger
by changing vane angle depending on the engine speed.

Answer 2

True

Question 3

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.

Answer 3

Charge Cooling

Question 4

Which statement is false regarding downsized engines?

Answer 4

They have better noise and vibration characteristics.

Question 5

Which statement is false regarding homogeneous charge compression ignition (HCCI) engine?

Answer 5

Inhomogeneous air-fuel mixture and high portion of diffusion flame.

Question 6

What is the main purpose of late post injection (after end of combustion) in diesel engines?

Answer 6

To activate after-treatment system by increasing exhaust temperature.

Question 7

Which statement is false regarding Methanol as an alternative fuel for SI engines

Answer 7

It has higher heating value than gasoline.

Question 8

Application of biodiesel can decrease pollutant emissions since it is _________ fuel so it can
promote complete combustion.

Answer 8

Oxygenated

Question 9

Which statement is false regarding series type hybrid vehicles?

Answer 9

They can deliver power to wheel directly using ICE

Question 10

Full hybrid type usually has longer mileage than micro/mild type hybrid vehicles by allowing
external charging.

Answer 10

False

Question 11

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

Answer 11

False

Question 12

Internal Energy is a _____ function and heat (or work) is a ___ function.

Answer 12

point/path

Question 13

How many crank angle degrees are required to complete an engine cycle for 2-stroke engine?

Answer 13

360

Question 14

Which of the following statements regarding thermodynamics is false?

Answer 14

in ideal gas equation. pressure is inversely proportional to temperature.

Question 15

Which of the following statements holds true for the ideal Otto Cycle (Theoretical) during combustion?

Answer 15

constant volume

Question 16

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.

Answer 16

37.5%

Question 17

Which of the following statements regarding gasoline/diesel engines holds true?

Answer 17

conventional diesel combustion is governed by diffusion flame (heterogeneous combustion)

Question 18

Compared to internal combustion engines, external combustion engines generally have higher thermal efficiency because of much simpler engine structure and less requirement for cooling.

Answer 18

False

Question 19

Four stroke engine has constant rotational force because work is produced in every rotation.

Answer 19

False

Question 20

The stoichiometric/theoretical air is the exact quantity of air necessary to provide enough oxygen for complete combustion.

Answer 20

True

Question 21

The engine size normalized work per cycle divided by the volume displaced per cycle is the:

Answer 21

mean effective pressure

Question 22

(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.

Answer 22

CompressionW

Question 23

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

Answer 23

60.1%