250+ TOP MCQs on Modern Common Rail Fuel Injection System and Answers

Automotive Engine Auxiliary Systems MCQs on “Modern Common Rail Fuel Injection System”.

1. How are the injectors activated in a modern common rail fuel injection system?
a) Spring
b) Solenoid valve
c) Rotor
d) Motor
Answer: b
Clarification: The fuel injectors present in the modern common rail fuel system are activated by the solenoid valve. Solenoid valves and the fuel pump are electronically controlled. Thus, the common rail serves as the high-pressure reservoir independent of the engine speed.

2. Which of the following helps in the increase of the engine torque at lower engine speeds?
a) Throttle body injection
b) The common rail injection system
c) Port injection
d) Retarded post-injection
Answer: b
Clarification: The common rail injection system, the injection pressure is possible even at low engine speeds which leads to more complete combustion of the fuel. It also increases the engine torque in the lower engine speed ranges.

3. In which type of injection mode the exhaust gas temperature for the regeneration of the particulate filter is increased?
a) Pilot injection mode
b) Retarded post ignition mode
c) Main injection
d) Double pre injection
Answer: b
Clarification: After the main injection phase, after which post-injection spurt of fuel is added, which reduces soot emissions. Finally, after upto 180 degrees of the crankshaft, a retarded post ignition occurs, which acts as a reducing agent for NOx and increases the exhaust gas temperature for the regeneration of the particulate filter.

4. How many times is the fuel being injected in one cycle of a modern automotive diesel engine?
a) 5-7
b) 7-10
c) 4-5
d) 10-12
Answer: c
Clarification: In modern automotive diesel engines, the fuel is not injected once in a cycle. Instead, the fuel injection is done upto 4-5 times in one cycle. There are different modes of injection depending on the time they have been injected.

5. Which of the following is not a property for injector open time duration?
a) Density of fuel
b) Dynamic compressibility
c) Injection pressure
d) Engine temperature
Answer: d
Clarification: The fuel is directly injected into the combustion chamber, the fuel mass flow would depend upon the difference between the injection and combustion chamber pressure,the density of fuel and dynamic compressibility of the fuel.

6. Which of the following is an example of a radial piston pump?
a) Low-pressure pump
b) High-pressure pump
c) Common rail
d) ECU
Answer: b
Clarification: Radial piston pump is an example of a high-pressure pump that generates high pressure in the accumulator, the rail independent of engine speed, and injected fuel quantity. The engine drives the pump through the coupling, gear wheel, chain, or toothed belt.

7. Which of the following does not depend on the fuel quantity injected?
a) System pressure
b) Duration of injection
c) Size and shape of the nozzle
d) Alternator speed
Answer: d
Clarification: The fuel is injected in the engine combustion chamber by the injection nozzle of an injector controlled by a solenoid-operated valve. The injector receives its operation signal from ECU. The system pressure, the duration of injection, and the size of the nozzle determine the fuel quantity injected.

8. Which of the following valve guards the system against excess pressure?
a) Pressure limiter
b) Inlet
c) Outlet
d) Both inlet and Outlet
Answer: a
Clarification: The fuel pressure in the rail is independent of engine speed and the injected fuel quantity. Flow limiters protect the system against the consequences of a potential leak of the injector. A pressure limiter valve guards the system against excess pressure.

9. How many numbers of engine variables are individually controlled in a common rail fuel injection system?
a) 1
b) 5
c) 7
d) 3
Answer: d
Clarification: The combustion behavior in diesel engines is affected by three variables,which are the timing of injection start, duration of injection, and discharge curve which all are individually controlled in a common rain fuel injection system.

10. Which among the following is not a component of the common rail fuel injection system?
a) ECU
b) Injector
c) Spark plug
d) Electric fuel pump
Answer: c
Clarification: The ECU takes the reading from the sensor based on the reading the ECU controls the fuel delivery from the electric fuel pump with prefilter and send the fuel to the high-pressure pump with a pressure regulator valve and then fuel is sent to the common rail than with the injector the fuel is injected.

11. Which among the following is the correct full form of ECU?
a) Electrical control unity
b) Electrical control unit
c) Electronic control unity
d) Electronic control unit
Answer: d
Clarification: The ECU is an electronic control unit. The ECU has various program maps stored in it. The ECU controls the fuel pressure in the common rail, integrated diagnosis-sensor monitoring and malfunction recognition, and other supplementary functions.

12. How much amount in millimeter cube of fuel is injected in a pilot injection phase?
a) 1
b) 2
c) 5
d) 7
Answer: a
Clarification: The pilot injection also called a pure injection which is a short bust of fuel before the main injection during each combustion cycle is in the range of 1millimeter and 50-millimetercube for full load main injection. The injection duration is about 1 to 2milliseconds.

13. Which is the sensor used to sense the pressure of the common rail?
a) Rail pressure sensor
b) Mass airflow sensor
c) Oxygen sensor
D) Thermostat
Answer: a
Clarification: The fuel from the fuel tank is pumped by a low-pressure electric fuel pump through a filter, to the high-pressure pump, which builds up the high pressure in the common rail with the help of a pressure regulator valve controlled by ECU through a rail pressure sensor.

To practice MCQs on all areas of Automotive Engine Auxiliary Systems,