What is Engines: Definition and 300 Discussions

An engine or motor is a machine designed to convert one form of energy into mechanical energy. Heat engines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common example of a heat engine, in which heat from the combustion of a fuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft. Electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and ultimately motion.

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  1. Astronuc

    Lifetimes of jet aircrafts and their engines

    I found this article today. Jalopnik - Here's How Often Airlines Replace the Jet Engines on Passenger Planes https://jalopnik.com/how-airlines-decide-to-replace-jet-engine-boeing-airbus-1850275010
  2. Pythagorean

    Stirling Engines for Home Power

    Would it be a feasible power source to have several Stirling Engines sticking through an outdoor wall near your fire place in a cold climate? Issues I can think of: Presumably it would be a heat sink and require you to consume more firewood. Engineering it to not have passive leaks might be...
  3. BarChen

    Become a Propulsion Engineer - Learn to Work with Rockets & Spacecraft

    Hi guys, I'm about to start my degree in a few months and I know what field I want to major in but I don't know what track I should take. In the future I want to work with rockets and spacecraft engines, I want to help develop the new generation. Correct me if I'm wrong but it's called a...
  4. Benjies

    Subsonic airbreathing engines and inlet blade angle

    Hello! My background in propulsion is extremely lackluster with airbreathing engines, so any help is appreciated with the following questions. I understand blade pitch is highly variable for turbofans which operate near the speed of sound, to avoid any localities on the blades reaching the speed...
  5. moriah

    Regular Grade Gas and its Effects on Car Engines

    Is regular grade gas detrimental to a car’s engine?
  6. M

    Internal Combustion Engines: Liquid Gasoline or Vapor?

    In an Internal Combustion Engine, does liquid gasoline itself burn/combust, or is it the gasoline VAPOR emitted from the liquid gasoline by evaporation that burns/ combusts? (assuming that Oxygen is present in the Air and Fuel mixture)
  7. voltech444

    Automotive Ozone Enhanced Combustion of Water/Diesel Emulsion in CI Engines

    I have a single cylinder 5kW diesel generator to use for fuel efficiency and emissions reductions improvement experiments. I built an emulsifier out of an old drill press and paint cans. It's basically just a spinning cylinder inside another cylinder to get a lot of shearing force. The...
  8. L

    Engineering Reviewing Efficiency of Otto & Diesel Cycle Heat Engines

    Hi, i have this question and don't understand it. can somebody explain what i have to do. i know a ideal engine is a engine running on carnot cycle i what the cycles are i don't know what relative efficiency is and what there looking for (Q) Review the relative efficiency of ideal heat engines...
  9. L

    Engineering Evaluate 2-stroke & 4-stroke Diesel engines therm & mechanical efficiency

    Evaluate 2-stroke & 4-stroke Diesel engines performance in terms of thermal & mechanical effiniecy HAs anybody got any links. all i can find is for petrol (2-stroke and 4-stroke). Is what i got so far any good?Thermal In a 2-stroke power stroke compared to a 4-stroke power stroke thermal...
  10. ZdMh

    About difference in Velocity and motion in Jet engines

    I was watching a video about jet engines, and it was obvious for me and for the instructor that if we compress air at high speed from the gas turbine inlet, then after multiple stages collide with the turbines blades inside, the body will move in the sense of difference in velocity, so forward...
  11. B

    Automotive Two IC Engines: Comparing Torque Curves

    Hello there , hopefully someone can shed some light on this for me . let's say you have two IC engines . all variables are the same . Engine A has a completely flat torque curve at 500’ lbs to 550’ lbs . Engine B has a torque curve that starts out at 450’lbs but gradually makes its way to 650’...
  12. R

    How do we maintain the RPM of turbo pumps in liquid rocket engines?

    How do we maintain the RPM of turbo pumps in liquid rocket engine ? and how do we control it ? and in the case of electric pump fed engine (like rocket labs's rutherford engine) is easy but how we do it for other liquid propellant engines ?
  13. R

    Understanding High Thrust of Vacuum Rocket Engines

    Why do vacuum rocket engine always producing high thrust than sea level rocket engine ? for example spacex's merlin vacuum engine produce more thrust than merlin sea level engine. And it is due to the big nozzle with large area in vacuum engine because when the flow reaches mach 1 in the throat...
  14. L

    Turbocharging carbureted petrol 2 stroke engines

    Hi everyone, online I ve seen some images about 2 stroke carbureted turbo (motorcycle derivation engine). Now.. In the past in this forum some members spoke about turbocharging 2 stroke but not in sufficient detail. The intake and the exhaust are open at the same time and there are no valves...
  15. M

    Automotive Exploring Combustion Engines for Cars & Planes: Student Research Ideas

    Hi All, I am helping a student (9th grader) develop a research topic related to his interests in physics for an independent study program he is applying for at our school. My background is Geology, so I am not too knowledgeable regarding topics in physics. This student is interested in...
  16. PCarson85

    Multiple constraints: Connecting rods for high performance engines

    Summary:: How to combine two formulas to find the material index Attached is the problem I am having trouble understanding. I have been able to do the first two combinations by transposing for A in the mass equation then subsituting into the stress equation. The next combinations (in red box)...
  17. E

    Thermodynamic sign convention for heat (i.e. in heat engines)

    Just to clarify, I'm aware of the two equivalent expressions of the first law ##\Delta U = Q + W## and ##\Delta U = Q - W## when applied to a certain system, though my question is primarily about ##Q## - for which, as far as I am aware, the convention is almost universally that ##Q > 0## if heat...
  18. E

    Engineering Efficiency of Heat Engines & Refrigerators: Is Impossible Possible?

    For the heat engine: First I converted all the temperatures to Kelvin, ηmax=1-(333)/(1000)=0.667 ηclaim=(1*10^3)/(1.75*10^3)=0.5714 So the heat engine seems to be less efficient than a Carnot heat engine which means it can exist. For the refrigerator: COPmax=(253)/(363-253)=2.3...
  19. M

    Engineering Thermodynamics - Second Law: 2 Heat Engines Connected Between 3 Metal Blocks

    Hi, I posted a similar question recently and gained some insight on these types of problems. However, I am slightly stumped on how to approach this variation of the problem. So I know that: - there is no net change in enthalpy of the blocks and the engine as the processes are reversible -...
  20. Prabs3257

    Carnot engines in series

    I know i have to use the efficiency formula and everything is fine but i don't know how to find T its the only unknown in my equation can someone please tell me how to find T . In the solution they got the value of T by equating the work done by the two engines , but why is their work done equal ?
  21. M

    Is ablative laser propulsion a better option than Ion engines?

    I’m trying to find something that can replace Ion engines in my Star Wars story. Ablative laser propulsion seems like a good bet because it works in both atmosphere and a vacuum and just seems better than Ion engines.
  22. C

    Automotive Can anybody suggest some forum about internal combustion engines?

    Could anybody suggest some forums(or bbs(s)) of internal combustion engine? Hello guys, I'm a physics fan, recently I was doing some research of internal combustion engines, could anybody who could suggest some forums or bbs(s) of internal combustion engine? i need somewhere to find some...
  23. Mark44

    Auto/Motor Interesting Youtube videos on fixing nonworking engines

    I've recently viewed a bunch of YouTube videos by mustie1. Here's one, in which he repairs an old generator that hasn't run for years -- In other videos that I've seen, he takes mopeds, motorcycles, and a variety of things with small engines, and gets them running, even some with frozen...
  24. José Ricardo

    About the efficiency of engines

    if we had an entire car made of Starlite (a material that was created resistant to 18032 °F). Would the efficiency of the combustion engine be close to that of the electric and that of the electric would be almost 100% efficient? https://en.wikipedia.org/wiki/Starlite
  25. DracoMalfoy

    Kinematics: Two engines, One Rocket, and Displacement.

    Homework Statement A Rocket with an engine that causes a net acceleration of 4m/s^2 launches with an initial velocity of 20m/s. The engine fuel lasts for 0.8s. A secondary engine then fires causing a net acceleration of 2m/s^2 for 0.6s How far off the ground is the rocket when the secondary...
  26. M

    Gas Turbine Engines: Expansion Away From Compressors

    In a gas turbine engine(in aircrafts), why doesn't the gas after expansion move backwards towards the compressor? .How is it that it expands away from the compressor(rotating the turbine blades)? Will the pressure of air at the end of the compressor before the combustion chamber be higher than...
  27. M

    Automotive Good books to understand detonation in engines

    Please Suggest me some good books(introductory level) to understand detonation in engines.
  28. H

    Automotive Exhaust brake for gasoline engines

    Everything I've read about them has said they would be ineffective or have very minimal benefit due to lower compression on non-diesel engines and other factors. Yet I am aware of one that sold well in the '80's and '90's and was tremendously effective as a "mountain tamer" in the RV industry...
  29. Thomaz

    Other Best Search Engines for Academic Papers - arXiv and Beyond

    What are the best search engines of academic papers in your opinion? as of right now I'm only searching on arXiv :(
  30. granzer

    Why variable geometry nozzles are not used on rocket engines

    Why is it that variable geometry nozzles, like those found on jet engine(iris nozzles), are not used as rocket nozzle to provide better altitude compensation?
  31. R

    The diameter of the exhaust nozzle of jet engines

    Hello, Can anybody please tell me the typical diameter of the exhaust nozzle of a jet engine? I know, there are different types of engines and nozzle types also vary. For instance, I am interested to know the typical diameter of the nozzle of a turbofan engine. Thanks
  32. lc99

    Carnot Engines Question -- Composite Configuration Efficiency

    Homework Statement Homework EquationsThe Attempt at a Solution Trying to figure this out. So, I'm thinking that adding a extra resevoir for another engine will not add efficiency. It will should split up the W done by the heat reservoir. It just seems to make sense that way. So would the...
  33. scottdave

    Mortal Engines movie - Wired magazine looks at the science

    If you've seen a recent movie trailer with the entire city of London on some treads and able to move around - that is Mortal Engines. Wired magazine takes a look at the science that goes along with that, and even has a few "homework" problems to work out. :smile...
  34. M

    Limitation of the number of search terms in search engines

    Why does Google limit its searches with 32 terms? I think other search engines seems to not limit but adding more terms for some reasons such as filtering does not work, for example in Yahoo. Thank you.
  35. C

    Unlocking Realistic Rotational Collisions with Physics & Graphics Engines

    Hi all! I'm currently working on a graphics/physics engine. The following Wikipedia page was extremely helpful in making rectilinear collisions look natural: https://en.wikipedia.org/wiki/Elastic_collision#Two-dimensional Specifically, the very general vector form of the equation on the bottom...
  36. M

    Heat engines working over time

    Homework Statement An office with a volume of 52.5 m^3 uses a heat engine that outputs 1200 W. Suppose that, initially, the office has a pressure of 1 atm and 20 degrees Celsius before the heater is turned on. After 10 minutes (6000 seconds), what is the final air temperature? Homework...
  37. F

    Heat engines can organize thermal energy

    Hello, I am reviewing some thermodynamics and heat engines. Heat engines are cyclical machines able to convert a portion (just a portion) of the thermal energy extracted from a hot reservoir into mechanical work. The residual thermal energy must dump into a lower temperature reservoir...
  38. Delta Force

    Automotive Modern Inline Eight Gasoline Engines

    Could a modern inline eight gasoline engine be competitive with other designs, especially for high performance applications such as a limousine or supercar?
  39. T

    Electric motors vs internal combustion engines

    On average, which has higher power to weight ratio between the two? So on average, if both weighed the same, which one is going to have more power?
  40. Dusan Stan

    Minute physics video: Why Are Airplane Engines So Big?

    The video shows some optimisations on the turbofan engine and reaches the conclusion it needs to be about 4m. The premise is that accelerating more air a little is more efficient than accelerating less air to a higher acceleration and speed, fact mentioned in all aerodynamics books, and that...
  41. O

    Rear mounted engines vs. front mounted for UAVs

    What difference is there between the design of a UAV with a front-mounted engine and a UAV with a rear-mounted engine? can you just switch the placement of the engine and move the weight and fuselage around to fix the center of gravity to be able to fly efficiently and stably?
  42. D

    Conserving Momentum for Rocket Engines

    Homework Statement Homework Equations conservation of momentum Thrust of rocket engine = -u (dm/dt) u is the velocity of the gas being expelledAlso found this from Wikipedia, not sure if it is relevant The Attempt at a Solution For these kinds of problems I assume you need to apply...
  43. Delta Force

    Automotive Why Don't Engines Use More Steel?

    Are there any reasons why engines tend to use iron, aluminum, titanium (connecting rods), and even magnesium (engine blocks) components while steel is far less common?
  44. Rx7man

    Automotive HCCI Engines - Benefits, Complexity, and Alternatives

    I just don't quite get all the hubbub about HCCI engines... I understand the benefits of lean burns, high compression ratios, etc, but the requirement to use only compression to ignite just doesn't make sense to me considering the complications, unpredictability, etc required to get it to...
  45. S

    Automotive Air fuel ratio effects in diesel vs. petrol engines

    I'm a mechanic who is currently doing a study automotive engineering. Being someone who worked on both diesel and petrol cars I know what a higher or lower air fuel ratio (AFR) will do for both engines. However I don't fully understand how the following is possible. "Adding fuel in a diesel...
  46. elixer akm

    Thermal vs Mech. Efficiency of Engines: Petrol vs Diesel

    What is the difference between thermal efficiency and mechanical efficiency of an engine...and which engine is more efficient ..petrol or diesel
  47. bigfooted

    Engineering Aircraft engine design books from 1900-1920

    I'm interested in the knowledge that was available to aircraft engineers in the period 1900-1920. specifically the thermodynamics and mechanical engineering knowledge generally available, like in how much detail were the calculations on the performance, or the cooling of engines done, how...
  48. Maximilian Popelier

    Question about Jet engines (thermodynamics)

    Hi, I need help I got a project for school about jet engines. They say bysubstitution of equations 5.1, 5.2, 5.5 and 5.6 butI don't know the steps how i get t0 the last formule. Thank you Maximilian Popelier
  49. P

    Thermodynamics: questions about vacuum engines

    Hi, I am trying to understand which thermodynamics process or processes could model a vacuum engine (mostly known by the name "flamelickers") and similar engines.. In a vacuum engine you have a cylinder and piston system that draws hot air from a heat source, cools it and mechanical work is...