Physics 8 Lesson 28: Heat engine
1.2. Four stroke engine
1.3. Engine performance
The efficiency of a heat engine is determined by the ratio between the heat successfully converted to mechanical energy and the heat released by the burned fuel.
– In there:
A: The work done by the engine (J), is equal to the amount of heat converted into mechanical energy.
Q: Heat released by the burned fuel (J)
2. Illustrated exercise
2.1. Form 1: Find car engine performance
A car travels a distance of 100 km with an average pulling force of 700 N, consuming 5 liters of gasoline (about 4 kg). Calculate the efficiency of a car engine.
A = Fs = 700.10000 = \(7.10^7J\)
So, the efficiency of the car engine is: \(H=38.04\)%
2.2. Form 2: State harmful effects of heat engines
In your opinion, heat engines can cause any harm to our living environment?
Harmful effects of heat engines on the environment:
Environmental pollution due to exhaust gases of many toxic engines.
The heat released by the engine contributes to an increase in the temperature of the atmosphere.
3.1. Essay exercises
Question 1: The engine of an airplane has a capacity of 2.106 W and 32% efficiency. So with a ton of gasoline, how long can the plane fly? Knowing the heat capacity of gasoline is 4.6.107 J/kg.
Verse 2: A water pump after consuming 8 kg of oil can deliver 900 m3 10 m high water. What is the efficiency of that pump? Knowing the heat capacity of the oil used for the pump is 4.6.107 J/kg, the density of water is 1000 kg/m3.
Question 3: With 2 liters of gasoline, how many kilometers will a motorbike with a capacity of 3.2 kW traveling at a speed of 45 km/h travel? Knowing the efficiency of the engine is 25%, the heat output of gasoline is 4.6.107 J/kg, the density of gasoline is 700 kg/m3.
Question 4: Calculate the efficiency of the car engine knowing that when the car is moving with a speed of 72 km/h, the engine has a capacity of 20 kW and consumes 20 liters of gasoline to run 200 km. The heat capacity of gasoline is 4.6.107 J/kg.
3.2. Multiple choice exercises
Question 1: Heat engines are:
A. Engine in which all the energy of the fuel is burned and converted into mechanical energy.
B. Engine in which part of the fuel’s energy is burned converted to heat.
C. Engine in which part of the fuel’s energy is burned converted to mechanical energy.
D. Engine in which all the energy of the fuel is burned and converted into heat.
Verse 2: Which of the following is not a heat engine?
A. Jet engines.
B. Motorcycle engine.
C. The engine runs the generator of a hydroelectric power plant.
D. The engine runs the generator of a thermal power plant.
Question 3: The strokes of a 4-stroke engine take place in the following order:
A. Fuel intake, fuel combustion, fuel compression, air release.
B. Exhaust, absorb fuel, compress fuel, burn fuel.
C. Fuel intake, fuel compression, exhaust gas, fuel combustion.
D. Fuel intake, fuel compression, fuel combustion, air release.
Question 4: Which of the following statements about the efficiency of a heat engine?
A. Performance indicates whether the engine is strong or weak.
B. Efficiency indicates how fast or slow the motor does work.
C. Efficiency indicates the amount of heat released when 1 kg of fuel is completely burned in the engine.
D. Efficiency indicates how much of the heat generated by the burned fuel is successfully converted into useful work by the engine.
Through this Heat Engine lecture, students need to complete some of the objectives given by the lesson, such as:
State the definition of a heat engine
Based on the model or drawing of a 4-stroke engine, it is possible to describe the structure of this engine.
Write a formula for the efficiency of a heat engine. Solve simple heat engine problems.