"Heat Engine" Mechanical energy, internal energy and their conversion PPT courseware 3

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"Heat Engine" Mechanical energy, internal energy and their conversion PPT courseware 3

Question: What happens when water boils?

Where does the energy to push the plug come from?

Demonstration experiment:

Phenomenon: The cork breaks out; "white gas" is produced at the mouth of the tube.

Explanation: Water vapor does work on the cork, its internal energy decreases, its temperature drops, and the water vapor liquefies into small water droplets.

When working: Internal energy is converted into mechanical energy

Application: Heat engine

1. Types of heat engines

steam engine

internal combustion engine

steam turbine

Jet engine

rocket etc.

Heat engine: A device that converts the internal energy released when fuel is burned into mechanical energy.

Internal combustion engine: A heat engine in which fuel is burned directly in the engine cylinder to produce power.

Common internal combustion engines: gasoline engine diesel engine

2. Structure of internal combustion engine

(1)Gasoline engine (2)Diesel engine

①Structure ①Structure

②Working principle ②Working principle

③Complete working process of gasoline engine

suction stroke

The intake valve opens and the exhaust valve closes. The piston moves from the upper end to the lower end, and the fuel mixture consisting of gasoline and air is sucked into the cylinder from the intake valve.

Compression stroke

Both the intake and exhaust valves close, the piston moves upward, the fuel mixture is compressed, the pressure increases, and the temperature increases.

Mechanical energy is converted into internal energy.

exhaust stroke

The intake valve closes, the exhaust valve opens, and the piston moves upward to expel exhaust gases from the cylinder.

Want to discuss:

What are the similarities and differences between the working processes of gasoline engines and diesel engines?

Same point

1. The basic structure and functions of the main components are similar.

2. Each workpiece cycle goes through four strokes: suction stroke, compression stroke, power stroke, and exhaust stroke.

3． Among the four strokes, only the power stroke performs external work, and the remaining three strokes are completed by the inertia of the flywheel.

4. In one working cycle, the piston reciprocates twice, the flywheel rotates twice and does work once.

difference

1. The structures are different: a gasoline engine has a spark plug on the top of the cylinder, while a diesel engine has a fuel injector on the top of the cylinder.

2. Different fuels: the fuel of gasoline engines is gasoline, while the fuel of diesel engines is diesel.

3． The suction is different: the gasoline engine sucks in a mixture of gasoline and air, while the diesel engine only sucks in air.

4. Ignition is different: gasoline engines have spark-ignition ignition, while diesel engines have compression-ignition ignition.

5. Efficiency of heat engine

Efficiency of a heat engine: The ratio of the useful work done by the heat engine to the heat released by complete combustion of the fuel. It's called the efficiency of the heat engine.

Incomplete combustion of fuel, heat loss after cylinder components absorb heat, heat taken away by exhaust gas, and energy consumed to overcome friction and perform work are all causes of energy loss. Therefore, improving the efficiency of heat engines can improve fuel utilization.

Ways and methods to improve thermal engine efficiency:

(1) Reduce various heat losses as much as possible, ensure good lubrication, and reduce the energy consumed by overcoming friction;

(2) Make full use of the energy of waste gas and improve fuel utilization, such as using waste gas from thermal power stations to provide heat. This kind of thermal power station that provides both power and heat has much higher fuel utilization than ordinary thermal power stations.

Class exercises:

1. The working process of a four-stroke gasoline engine consists of four strokes ( ), ( ), ( ), and ( ).

2. In a four-stroke gasoline engine, the ( ) stroke converts mechanical energy into internal energy, and the power stroke converts ( ) energy into ( ) energy.

3. What is sucked into the cylinder of a gasoline engine is ( ), and the ignition method is ( ). What the diesel engine sucks into the cylinder is ( ), and the ignition method is ( ).

4. The speed of the flywheel of a four-stroke gasoline engine is 3600R/min, and it does external work ( ) times per second.

Example: To boil 5kg of water at 40°C, how many kilograms of dry firewood need to be burned completely? (It is known that the calorific value of dry firewood is 1.2×107J/kg, the external pressure is standard atmospheric pressure, and all the heat released by complete combustion of the fuel is absorbed by water)

Solution: Q suction = cm (t-t0) = 4200J/(kg·0C)×5kg×600C

=1.26 ×106J;

Q put = Q suck

m1=Q put/q

= 1.2×106J/(1.2×107J/kg)=0.1kg

The energy released by the combustion of fuel is used to start the heat engine, but not all of this energy is used to do useful work.

Heat engine efficiency: The ratio of the energy used to do useful work to the energy released by complete combustion of the fuel.

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For more information about the PPT courseware "Thermal Engine Mechanical Energy Internal Energy and Its Transformation", please click the Thermal Engine ppt Mechanical Energy Internal Energy and Its Transformation ppt tag.

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Update Time: 2024-07-02

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