How does a fuel engine convert heat into mechanical work?

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Discussion Overview

The discussion revolves around the mechanisms by which fuel engines convert heat energy into mechanical work, specifically focusing on internal combustion engines and steam engines. Participants explore the underlying principles, efficiency variations, and the processes involved in these energy transformations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how the burning of fuel is transformed into mechanical work, expressing uncertainty about their understanding.
  • Another participant explains that in internal combustion engines, thermal energy is generated from the combustion of fuel, which creates pressure that pushes pistons or turbines, ultimately producing mechanical work.
  • The explanation includes details about how the expansion of hot gases in jet or rocket engines relates to momentum and thrust.
  • A steam cycle is described as involving the heating of water to produce steam, which expands and drives turbines, similar to internal combustion engines.
  • Efficiency of various engine types is discussed, noting that thermal efficiencies can vary significantly based on design and technology, with specific percentages provided for nuclear and fossil fuel power plants.
  • A participant shares a resource link to an animation illustrating the internal workings of a car engine, suggesting that the cycles involved are similar across different engine types.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and detail regarding the conversion processes, with no consensus on the efficiency metrics or the best design approaches. The discussion remains open-ended with multiple perspectives on the topic.

Contextual Notes

Participants mention specific efficiencies for different types of engines, but these figures depend on various factors such as design and operational conditions, which are not fully explored in the discussion.

fawk3s
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Seems like a stupid question, to me. But well, I am stupid aswell, so it fits me.

Its something I've been thinking about lately. How is the heat/buring of the fuel transformed into mechanical work?
I've had some ideas but they are mainly stupid and the loss of energy would be massive in those.

So how do fuel/steam engines work?

Thanks in advace,
fawk3s
 
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In an internal combustion engine, the release of stored chemical energy creates thermal energy. The combustion products in the form of hot gas produced a greater volume, or greater pressure, than the products. The pressure pushes a piston, or pushes through a turbine to the lower pressure exit downstream. Pressure on an area produces a force. The force on a piston is transmitted to a crackshaft, which produces a torque, or the force on a set of turbine blades causes moment on the blade, which tranmits a torque to the shaft of the turbine.

In addition, the expansion of hot gases in a jet or rocket engine also represents a change in momentum. The thrust or force of a jet/rocket is related to the exhaust (exit) velocity of the hot gases.

A steam cycle works much the same way. Liquid water is pumped into a heat exchanger (boilder) where it absorbs heat and changes phase going from liquid to gas. The gas occupies greater volume, and by virtue of the conservation of mass (continuity), the gas, which is constrained on one or two dimensions expands. That expansion means the gas has a higher velocity/momentum than the liquid. The steam flow passes through a turbine, and the momentum/energy of the flow pushes on the turbine blades, which like the example of the combustion turbine blade above, causes a torque on the turbine shaft.

A rotating shaft can be used via a transmission system to turn wheels of a vehicle (car, truck, motorcycle) or propeller (aircaft or ship) or generator shaft (electrical generator) or a motor or mill machinery.

So it goes something like thermal energy -> mechanical rotational energy, and optionally mechanical energy -> electrical energy
 
Last edited:
Hm, I wasnt so wrong after all..
Thanks, helped much !
 
The efficiency of the process is quite variable.

Commercial nuclear power plants based on the steam (Rankine) cycle have thermal efficiencies of ~32-37% depending largely on the turbine designs (particularly the blade designs).

Fossil (coal, oil, gas - fired) power plants have efficiencies of 34-40% depending on the amount of superheat.

Gas fired (Brayton, combustion turbine) can achieve ~42% efficiency. Aeroderivative combusion turbines have become quite efficient compared to combustion turbines of 30 to 40 years ago.

Adding a steam (Rankine) cycle to a gas-fired combustion turbine cycle can yield 53-62% thermal efficiency.
 

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