Heat Engines: Otto and Diesel

• Heat engines are technical devices that convert energy in the form of heat or thermal energy into mechanical work.

Combustion Engines

• Combustion engines use the thermal energy of combustion gases produced by burning a fuel in a cylinder to drive a cylinder piston and perform mechanical work.

Otto Engine

• The Otto engine was invented by Nikolaus August Otto (1832-1891).

The Working Cycles

• Intake stroke:
  • The piston moves downward, drawing a gasoline-air mixture from the carburetor through the intake valve while the exhaust valve is closed.
• Compression stroke:
  • The piston moves upward, compressing the gas with both valves closed.
• Power stroke:
  • Both valves are closed; the gasoline-air mixture is ignited by the spark plug, causing an explosion that drives the piston down and performs work
• Exhaust stroke:
  • The piston moves upward again, expelling the combustion gases through the open exhaust valve.

Diesel Engine

• Rudolf Diesel invented the diesel engine (1858 - 1913)
• The diesel engine operates on the same principles as the Otto engine but does not require spark plugs.
• A key feature is the self-ignition of the injected fuel by means of combustion air heated by compression.

Differences between the Otto Engine and Diesel Engine

• Otto Engine:
  • External ignition.
  • Needs spark plugs.
  • Air and fuel mix externally in the carburetor.
  • Operates at temperatures of 400° C – 600° С.
  • Has an efficiency of approximately 25%.
• Diesel Engine:
  • Self-ignition.
  • Does not need spark plugs.
  • Air and fuel mix internally in the combustion chamber.
  • Operates at temperatures of 700° С- 900° С.
  • Has an efficiency of approximately 33%.

Environmental Impact

• Burning fossil fuels (gasoline, diesel), which are available in finite amounts, uses them for energy instead of other purposes like medicine.
• Low efficiency means much of the energy is released as waste heat.
• Noise pollution can cause illness
• Exhaust gases and waste harm the environment.
• Increasing carbon dioxide in the atmosphere contributes to the greenhouse effect.
• Exhaust gases harm human health.
• Particulate matter (especially from diesel fuels) causes cancer.
• New roads displace nature and animal habitats.
• Industry and drivers must work to protect the environment.
• More efficient engines and streamlined vehicles reduce emissions and fuel consumption.
• Catalytic converters (Otto engines) and particulate filters (Diesel engines) clean exhaust gases.
• Alternative fuels include biodiesel, solar, and hydrogen.
• Eco-friendly driving includes avoiding short trips, using low speeds, driving predictably, and maintaining proper tire pressure.

Steam Turbines

• Power plants use coal, gas, or oil as fuel
• Chemical energy from combustion turns into thermal energy to boil water into steam.
• The steam drives the turbine blades to do mechanical work.

Function

• Steam is directed onto the blades.
• Steam transfers kinetic energy to the rotor.
• The rotor spins faster (rotational energy).
• In a multistage turbine, the steam flows onto a second rotor.
• As energy is gradually released, the steam slows down and its temperature decreases. This causes the steam to expand, so the turbine surface area must grow incrementally.
• Steam turbines have an efficiency of 35-40%.
• The remaining energy increases the turbines' internal energy and surrounding environment.