Lessons 30–31 · 2 lessons · P. Habibullayev, A. Boydedayev, A. Bahromov, K. Suyarov, J. Usarov, M. Yuldasheva. Physics Grade 9, revised and expanded 3rd edition. G‘afur G‘ulom Publishing House, Tashkent, 2019
31
Heat engines and protecting nature
Textbook: pp. 87–88
GoalKnow how heat engines affect the environment and how the harm can be reduced.
New words
harmful gases · zararli gazlargreenhouse effect · issiqxona effektiozone layer · ozon qatlamialternative energy · muqobil energiya
Explanation
Heat engines are essential in transport, electricity generation and industry, but burning fuel releases carbon dioxide CO₂, carbon monoxide CO, nitrogen oxides and soot into the atmosphere. CO₂ strengthens the greenhouse effect and contributes to climate warming; carbon monoxide is poisonous. Burning 1 kg of petrol produces about 3 kg of CO₂. Because efficiency is below 100 %, a large part of the fuel’s energy ends up as heat in the surroundings. Some coolants (freons) formerly used in refrigerators damaged the ozone layer in the atmosphere, so they have been replaced by ozone-safe substances. Ways to reduce harm: raise engine efficiency, use filters and catalytic converters, public transport, electric transport, and solar and other renewable energy. Never run an engine in a closed garage: carbon monoxide can kill.
Worked examples
If a car’s efficiency is 30 %, 1 kg of petrol (46 MJ) gives useful work 0.3·46 = 13.8 MJ and the remaining 32.2 MJ is lost as heat to the surroundings.
By the rough figure of 3 kg CO₂ per kg of petrol, a car burning 10 kg of petrol emits about 30 kg of CO₂. Saving fuel and shortening trips therefore helps nature.
Class activity
Mini-project: write 3 simple measures for your family or school that reduce CO₂ (walking, public transport, reducing heat loss when heating a room) and explain each benefit in one sentence. Do not work with any fuel or engine.
Practice
1
How do heat engines harm the environment? Give two examples.
CO₂ emissions warm the climate; carbon monoxide and soot pollute the air.
2
A car with efficiency 30 % gets how many MJ of useful work from 5 kg of petrol (q = 46 MJ/kg)?
69
3
Name three ways of reducing damage to the environment.
Raising efficiency, public and electric transport, solar energy, filters and catalytic converters (any three).
4
Why is starting an engine in a closed garage dangerous?
The exhaust contains poisonous carbon monoxide that builds up in a closed space and causes poisoning.