Heat engines and ecology

Heat engines include the steam engine and steam turbine, the internal combustion engine (petrol and diesel) and jet engines. In a steam plant the heater is the boiler, the working substance is steam, and the cooler is the condenser or the atmosphere. A four-stroke petrol engine has the strokes: intake (the mixture enters), compression (it heats adiabatically), power stroke (a spark ignites the mixture and the gas expands and does work) and exhaust (the combustion products are expelled). In a diesel only air is compressed, and it heats enough to ignite the fuel by itself; the compression ratio is high, so a diesel’s efficiency is higher than a petrol engine’s (about 35–40% against about 25–30%). In a jet engine the gas leaves the nozzle at high speed and by conservation of momentum a thrust force appears. Heat engines are vital for transport, electricity generation and industry, but burning fuel produces CO₂ (the greenhouse effect, global warming), nitrogen and sulphur oxides (acid rain), smoke and dust; so catalytic filters, better fuel, electric vehicles and renewable energy sources are important.