Automotive Temperature Control and Dynamics

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Questions and Answers

What is the primary factor influencing the required injection time for a given fuel mass?

The temperature of the fuel supply

The fuel injector's opening cross-section and pressure differential (correct)

The material of the intake manifold

The engine's rotational speed

In a solenoid fuel injector at rest, what force maintains the seal against the valve seat?

The fuel's own pressure

Air pressure from the intake manifold

A spring mechanism (correct)

Magnetic attraction from the solenoid coil

Approximately how far does the injector needle lift when the solenoid coil is energized?

0.05 mm

0.5 mm

1.5 mm

0.15 mm (correct)

What is the primary purpose of the pintle shape at the front of the injector needle?

To atomize the injected fuel (C) Signup and view all the answers

Which of the following accurately describes the benefit of low-temperature combustion (LTC) in relation to conventional diesel combustion (CDC)?

LTC results in lower soot formation due to a leaner mixture and reduced thermal NOx formation because combustion temperatures remain relatively low. (C) Signup and view all the answers

What role does the 'T plot' (Kamimoto-Bae diagram) play in understanding diesel combustion processes?

It visually represents the relationship between local equivalence ratio and local temperature, showing the progression of fuel elements through different combustion zones. (A) Signup and view all the answers

What component directly controls the duration of fuel injection in a multi-point injection (MPI) system?

The engine's electronic control unit (ECU) (B) Signup and view all the answers

During which operational conditions, besides cold start, does the engine control unit (ECU) typically command mixture enrichment?

During accelerations and full load operation (B) Signup and view all the answers

How does the use of high Exhaust Gas Recirculation (EGR) rates affect the combustion process in mixing-controlled LTC (PCCI) compared to conventional diesel combustion (CDC)?

High EGR rates in PCCI help maintain lower temperatures, reducing the risk of soot and NOx formation, unlike CDC where these emissions are more prevalent. (A) Signup and view all the answers

In modern engine systems, what is a common method to achieve cold-start enrichment, replacing a dedicated cold-start injector?

Extending the injection time of the port injectors (A) Signup and view all the answers

What is the primary reason why LTC results in increased CO and HC emissions compared to conventional Diesel Combustion (CDC)?

The leaner mixture in LTC leads to incomplete combustion, resulting in higher CO and HC emissions. (A) Signup and view all the answers

Why is fuel typically injected towards the intake valve during its closed period in a port-fuel-injection (MPI) system?

To minimize the amount of port wall wetting and enhance vaporization (C) Signup and view all the answers

How does the timing of ignition relate to the formation of soot and NOx in premixed LTC approaches?

Early ignition results in higher peak pressures and temperatures, leading to increased soot and NOx formation in premixed LTC. (C) Signup and view all the answers

What primary advantage does direct fuel injection offer in terms of mixture control compared with port fuel injection?

It enables more rapid and precise adjustments to mixture preparation due to reduced fuel transport delay. (D) Signup and view all the answers

What is a primary limitation of operating a lean mixture with throttling in an engine?

Elevated risk of misfiring. (B) Signup and view all the answers

How does direct fuel injection impact the engine's ability to operate with a fuel-lean mixture, especially at part-load?

It allows overall fuel-lean operation while maintaining a combustible mixture near the spark plug. (A) Signup and view all the answers

Compared to MPI systems, what is a key characteristic of fuel injection in Direct Injection (DI) systems?

Higher fuel pressure and shorter injection time. (A) Signup and view all the answers

What is the potential benefit of fuel vaporization within the cylinder in direct injection engines?

It cools the air charge, permitting higher compression ratios and delaying the onset of knock. (D) Signup and view all the answers

What is the primary function of a multi-hole nozzle injector in a GDI engine?

To improve spray dispersal, evaporation, and mixture preparation. (A) Signup and view all the answers

By approximately what percentage can direct injection potentially improve an engine's volumetric efficiency?

Up to 10% (A) Signup and view all the answers

What is a major drawback associated with GDI engines regarding emissions?

Elevated levels of particulate emissions. (A) Signup and view all the answers

In general, how does direct fuel injection benefit specific fuel consumption compared to port fuel injection, especially at part load?

It can significantly reduce fuel consumption, potentially by 15-25%. (D) Signup and view all the answers

What is a key disadvantage of direct fuel injection systems despite their efficiency benefits?

Higher system costs due to the need for increased injection pressure (A) Signup and view all the answers

In a continuous fuel delivery system for DI engines, what happens to the excess fuel not required for injection?

It is depressurized and returned to the low-pressure fuel circuit. (C) Signup and view all the answers

What type of pump is commonly used in the high-pressure circuit of a continuous-delivery DI system?

Three-barrel radial-piston pump. (B) Signup and view all the answers

What was the primary focus of early GDI (Gasoline Direct Injection) engines developed in the late 1990s?

Running a stratified lean mixture to improve fuel economy. (B) Signup and view all the answers

When does mixture preparation take place in a direct injection system, and how does this compare to time available in port fuel injection?

Mixture preparation occurs within the cylinder allowing for less time for mixing. (B) Signup and view all the answers

In a demand-controlled fuel delivery system for DI engines, what component is actuated by the ECU to regulate the quantity of fuel delivered to the rail?

Fuel supply control valve. (A) Signup and view all the answers

Compared to intermediate loads, during which situation is the air-fuel mixture for a homogeneous charge typically closer to stoichiometric?

During intermediate load conditions. (B) Signup and view all the answers

What is the relationship between alkane chain length and ignition quality?

Longer alkanes improve ignition quality. (B) Signup and view all the answers

Which statement is true regarding biodiesel and its cetane number?

Biodiesel's cetane number ranges from 40 to 60. (A) Signup and view all the answers

How does injection timing affect ignition delay (ID)?

Earlier injection leads to longer ID. (B) Signup and view all the answers

What primarily influences the temperature during combustion in diesel engines?

Fuel-air mixing. (C) Signup and view all the answers

Which factor does NOT significantly impact the ignition delay in diesel combustion?

Fuel viscosity. (C) Signup and view all the answers

In a multi-spray single-injection DI diesel engine, what is the role of optical laser diagnostics?

To assess interactions of fuel and chemical species. (D) Signup and view all the answers

What is a consequence of a larger amount of fuel injected into the engine?

Shorter ignition delay. (C) Signup and view all the answers

What does NOT affect the temperature during the mixing-controlling phase of combustion?

Catalytic converter efficiency. (A) Signup and view all the answers

In the combustion process of a diesel engine, what factor primarily regulates the combustion rate?

The fuel-air mixing process (B) Signup and view all the answers

What distinguishes diesel combustion from gasoline combustion?

Diesel combustion is characterized by spontaneous ignition. (A) Signup and view all the answers

Why can diesel engines achieve a higher compression ratio compared to gasoline engines?

Diesel engines are not constrained by knocking combustion, allowing for higher compression. (D) Signup and view all the answers

What is the primary role of the cetane number in a diesel engine?

To minimize the ignition delay period. (C) Signup and view all the answers

How is engine torque controlled in a diesel engine?

By modifying the amount of fuel injected per cycle. (D) Signup and view all the answers

What is the primary advantage of operating a diesel engine unthrottled?

It improves mechanical efficiency at partial loads. (A) Signup and view all the answers

What is the primary constraint on the fuel/air ratio at maximum engine power in a diesel engine?

The formation of excessive soot due to incomplete combustion. (C) Signup and view all the answers

What is the implication of a short ignition delay in a diesel engine? (Select all that apply)

It ensures that the maximum cylinder pressure and its derivative remain within acceptable levels. (C), It allows for a faster response to changes in engine load. (D) Signup and view all the answers

Study Notes

Temperature Control

Boosting heating systems is covered in section 15.5.3
Refrigerant circuit with expansion valve is discussed in section 15.5.4
R744-based refrigeration cycle is detailed in section 15.5.5
Temperature control is described in section 15.5.2

Engine-Vehicle Matching

Longitudinal dynamics are introduced in section 16.1.1 and 16.1.2
Equations of longitudinal dynamics are presented in 16.1.2
Acceleration and forces due to inertia are explained in section 16.1.3
Traction force at the wheels is discussed in section 16.1.4
Transmission efficiency is covered in 16.1.5
Vehicle performance is detailed in sections 16.2, 16.3.1, 16.3.2, 16.3.3, 16.3.4 and 16.3
Performance/performance index is covered in section 16.2
Coastdown method: procedures are described in 16.3.1, 16.3.2,16.3.3 and 16.3.5
Coastdown implementation on a test rig is in section 16.3.5
Gear ratio selection is explored in section 16.4
Overall gear ratio is in section 16.4.2
Vehicle fuel consumption is in section 16.4.3, 16.5. 16.5.2 and 16.5.3

Fuel Metering System for SI Engines

Spark-ignition engines use a premixed mixture of fuel vapor and air.
The engine induction/fuel systems prepare a mixture from ambient air and fuel.
The optimum air-fuel ratio in SI engines gives required power with lowest fuel consumption and maintains smooth/reliable operation.
Mixture requirements are expressed through equivalence ratios (e.g., for gasoline, roughly 14.6).
Mixture requirements vary with different operational loads, like idle, part load, and full load.
Operation at different loads has corresponding mixture requirements.
There are fuels used in SI engines like gasoline, ethanol, LPG, and natural gas.
Fuel characteristics impact combustion processes, knock, and mixture preparation.
Carburetor method controlled fuel flow/distribution to intake.
Single-point fuel injection system uses one injector upstream of throttle plate .
Multi-point fuel injection (MPI) uses separate injectors for each cylinder, closer to the cylinders, reducing issues of fuel-wall wetting and improving fuel distribution.
Fuel supply systems are discussed with examples of supply with fuel tank return and returnless systems.

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Description

This quiz covers critical concepts in temperature control systems, including heating systems, refrigeration cycles, and engine-vehicle matching. Sections delve into the dynamics of vehicles, traction forces, and performance metrics. Prepare to test your knowledge on how temperature and vehicle dynamics interplay in automotive engineering.