"Heat Engine" Mechanical energy, internal energy and their conversion PPT courseware 2

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"Heat Engine" Mechanical energy, internal energy and their conversion PPT courseware 2

1. Acquisition of internal energy:

Through the combustion of fuel, the chemical energy inside the fuel is converted into internal energy.

2. Utilization of internal energy:

1. Directly heat objects

2. Use internal energy to do work

Internal energy converted into mechanical energy

Fuel combustion converts chemical energy into internal energy, and then converts internal energy into mechanical energy through work

3. Heat engine

A machine that converts internal energy into mechanical energy

Types of heat engines

Steam engine, internal combustion engine, steam turbine, jet engine, rocket, etc.

Want to discuss

1. Among the four strokes, which strokes undergo energy conversion?

2. Which stroke gives the car power?

3. Which stroke discharges the exhaust gas from the car?

Ignition method: compression ignition

At the end of the compression stroke, the mist diesel fuel sprayed from the fuel injector burns violently when it encounters hot air, producing high-temperature and high-pressure gas, which pushes the piston downward and drives the crankshaft to rotate through the connecting rod.

Ignition method: pilot type

At the end of the compression stroke, the spark plug generates an electric spark, which causes the fuel to burn violently, producing high-temperature and high-pressure gas, which pushes the piston downward and drives the crankshaft to rotate through the connecting rod.

3. Calorific value of fuel:

1. There are many types of fuels, which can be divided into solid fuels, liquid fuels and gaseous fuels.

2. Burning different fuels of the same mass releases different amounts of heat.

3. Calorific value of fuel: The heat released by the complete combustion of 1kg of a certain fuel is called the calorific value of the fuel.

4. Unit of calorific value: J/kg

5. The symbol of calorific value: q

4. Fuel utilization:

think:

In the above example, Xiaoming used 1.5kg of bituminous coal to boil water. The heat released by complete combustion of these coals is 4.05×107J. Is the actual heat released 4.05×107J? Why? What about the actual amount of heat absorbed by the water?

The heat actually absorbed by water is called effectively utilized heat.

1. Furnace efficiency:

The ratio of the heat effectively utilized (heat absorbed by water) to the heat released by complete combustion of the fuel.

Formula: η=Q suction/Q release=cm△t/mq

2. Improve fuel utilization and save energy

1) Make coal fully burn: Grind the coal into coal particles and increase the air supply volume.

2) Increase the heating area and reduce the heat taken away by the flue gas:

3. Efficiency of a heat engine: The ratio of the part of energy used to do useful work to the heat released when the fuel is completely burned is 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 to improve heat engine efficiency and energy saving methods:

(1) Reduce various heat losses as much as possible, such as ensuring good lubrication and reducing 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.

calculate:

1. How much heat can be produced by completely burning 15 kilograms of charcoal with a calorific value of 3.4×107 Joules/kg?

2. How many kilograms of hydrogen need to be completely burned to obtain this amount of heat? (q hydrogen = 1.4 × 108 Joules/kg)

3. To boil 5kg of water at 40℃, how many kilograms of dry firewood need to be completely burned?

(It is known that the combustion value of dry wood 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)

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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 tab.

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Update Time: 2024-12-03

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