Question 1

When the unison ring in a variable nozzle (VN) type turbocharger is moved, which of the following changes?

Accepted Answer

C  Moving the unison ring in a VN turbocharger changes the vane pitch, which in turn alters the inlet flow area to control the exhaust flow and boost pressure.

Question 2

Which sound dampening principle is based on sound waves being reflected back toward their source?

Accepted Answer

Resonation involves the reflection of sound waves back towards their source, effectively reducing the transmission of sound by creating interference patterns that can cancel out or diminish the original sound waves.

Question 3

In a sound absorption type muffler, what is sonic energy converted to?

Accepted Answer

In a sound absorption type muffler, sonic energy is converted to friction, and then this friction is ultimately converted into heat. This process helps in reducing the sound emitted by the engine.

Question 4

What is the housing containing the muffler, catalytic converters, SCR, and diesel particulate filter (DPF) known as?

Accepted Answer

The housing containing the muffler, catalytic converters, SCR (Selective Catalytic Reduction), and diesel particulate filter (DPF) is known as the exhaust gas aftertreatment canister. This system is designed to reduce emissions from the exhaust of a diesel engine.

Question 5

Where would you most likely find a thermocouple pyrometer on a current highway diesel engine?

Accepted Answer

A thermocouple pyrometer is often used to monitor the temperature of the diesel particulate filter (DPF) to ensure it is operating within the correct temperature range for regeneration and to prevent overheating, which can damage the filter.

Question 6

Which of the following operating conditions is more likely to cause a diesel engine, catalytic converter to plug?

Accepted Answer

Light load, cold temperature operation is more likely to cause a diesel engine's catalytic converter to plug because under these conditions, the exhaust temperatures are too low to allow the catalytic converter to operate efficiently. This can lead to incomplete combustion and the accumulation of particulates and unburned hydrocarbons, which can clog the converter.

Question 7

Which of the following best describes the role of an exhaust gas recirculation (EGR) system on a current diesel engine?

Accepted Answer

The EGR system recirculates a portion of an engine's exhaust gas back to the engine cylinders, diluting the intake charge and reducing the oxygen content. This process lowers peak combustion temperatures, which in turn reduces the formation of nitrogen oxides (NOx), a major air pollutant.

Question 8

What happens when a wastegate actuator is in its default position?

Accepted Answer

In its default position, a wastegate actuator closes the wastegate, causing all exhaust gas to be routed through the turbine housing. This maximizes the amount of exhaust gas available to spin the turbocharger's turbine, increasing the engine's efficiency and power output.

Question 9

Technician A says that a VG turbocharger functions like a small turbo when engine loads are light. Technician B says that a VG turbocharger functions like a large turbo when engine output is high. Who is correct?

Accepted Answer

A Variable Geometry (VG) turbocharger adjusts its geometry to act like a small turbo at low engine loads for quick response and like a large turbo at high engine loads for increased airflow and power.

Question 10

Which of the following statements best describes how EGR functions to reduce NOx emissions?

Accepted Answer

EGR (Exhaust Gas Recirculation) reduces NOx emissions by recirculating a portion of the engine's exhaust back to the engine cylinders, which reduces the oxygen intake and lowers the combustion temperature, thereby reducing NOx formation.

Question 11

What is the functional difference between C-EGR and I-EGR?

Accepted Answer

I-EGR (Internal Exhaust Gas Recirculation) is managed within the cylinder head, utilizing the engine's own mechanisms (like valve timing) to recirculate exhaust gases, while C-EGR (Cooled Exhaust Gas Recirculation) involves external routing of exhaust gases through a cooler before reintroducing them into the intake.

Question 12

Which type of valve configuration is more likely to be used with quiescent combustion technology?

Accepted Answer

Parallel port valves are more likely to be used with quiescent combustion technology because they provide better air-fuel mixing and reduce the formation of soot and NOx emissions.

Question 13

When a turbocharger is set up to impart drive torque to the crankshaft, which of the following terms describes the system?

Accepted Answer

Compound turbocharging is the correct term because it refers to a setup where a turbocharger is used in conjunction with the engine in such a way that it provides additional drive torque to the crankshaft, enhancing the engine's efficiency and power output.

Question 14

What term does Detroit Diesel use to describe their compound turbocharger on DD-series engines?

Accepted Answer

Detroit Diesel refers to their compound turbocharger system as the Axial Power Turbine (APT) on DD-series engines. This system is designed to improve efficiency and performance by using an additional turbine in the exhaust stream to extract more energy.

Question 15

Technician A says that a DD axial power turbine (APT) uses a constant geometry (CG) turbine principle. Technician B says that Detroit Diesel claim their APT can add over 100 horsepower to engine output potential. Who is correct?

Accepted Answer

The answer of Technician A says that a DD axial...

Question 16

While pressure testing an isolated Cummins charge air cooler (CAC), the pressure drops from 30 psi to 25 psi in 15 seconds. Technician A says that the CAC is leaking. Technician B says that the pressure drop-off is within specification and the CAC can be returned to service. Who is correct?

Accepted Answer

The answer of While pressure testing an isolated Cummins charge...

Question 17

What is the function of the stainless steel liner used in the cylinder head exhaust tract of some diesel engine cylinder heads?

Accepted Answer

The stainless steel liner in the exhaust tract is primarily used for insulation to maximize the heat discharge to the turbine housing, improving the efficiency of the turbocharger.

Quiz 12: Engine Breathing