What is Engines: Definition and 301 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. 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...
  2. T

    Plane's Coanda's effect and jet engines sucking in air

    I saw a video recently describing the lift in terms of pressure. It stated that the Coanda's effect is important. That is the tendency of a fluid jet to flow a curved path. It stated that there is high pressure above the top of an air foil and low pressure below so the air drops or gets...
  3. C

    Crower steam expansion stroke for two stroke/rotary engines

    I was interested in whether it might be possible to incorporate a steam expansion power stroke into a two stroke or a rotary engine. The difference would be that unlike the convention Crower six stroke cycle there would be compressed air in the combustion chamber, without some sort of valve...
  4. Hercuflea

    Why do Stirling engines have low power/weight?

    I have heard that Stirling engines are not in wide use because they have a low power-weight ratio. Why is this? It would seem to me that the Beta type stirling engine (with 1 cylinder) would be very efficient because it only has like 3 major moving parts...flywheel crankshaft and piston and...
  5. The GodWhiz

    Physics Research in wireless energy transfer or Future space engines

    Hi, i am a 2nd year B.E student in India,and a new user to this site(sorry for any mistakes :) ) .My question is i want to do research that primarily concerns these 2 areas viz.Wireless energy transfer, and future space engines(starwhisps,solar sails,etc),is there any way to achieve my dream,i...
  6. Aestheticia

    Methane as a substitute for petroleum in combustion engines

    Dear engineering community: For many years now I have wondered why our internal combustion engines have not been adapted for methane in place of the various forms of petroleum products we currently use. Why? (1) Because we have a gargantuan ever-renewing source of methane in human garbage...
  7. Brian Teal

    IR heat reflectivity and engines

    A HUGE topic of conversation on many car forums, I thought I would bring it here. Many cars have chrome tin in the engine compartments to make them look flashy. However, for decades now, people say the chrome reflects the heat back onto the engine block and to paint the engine compartment black...
  8. D

    Thermodynamics and Carnot engines - university exam question

    Homework Statement A block of radioactive material is ti be used as a power source for a deep space probe which may be treated ideally as a single Carnot engine. Radioactive decay generates heat in the block at a rate Pin = dQin/dt and heat is extracted from the block to operate the probe at a...
  9. Dream Relics

    Steam engines -- A new idea, maybe....

    Why do we use water for steam engines? Why not something else? So, I have a question, or maybe it is an idea that i would like to share. So, sure, there are many finer points to the engineering of a steam turbine to make them work efficiently, and no doubt the designs have improved much since...
  10. Tulio Cesar

    How Do Carnot's Efficiency Formulas for Heat Engines Align?

    My question is: according to Carnot cycle, the maximum efficiency of a heat engine is given by 1 - T2/T1, where T2 is the temperature of the cold source and T1 the temperature of the hot source. So, accordingly, as higher T2 is for a same T1, lowest is the efficiency of the engine. But, the...
  11. S

    How Does a Heat Engine's Efficiency Affect Final Temperature and Work Output?

    Homework Statement Two identical tanks of water are at absolute temperatures ##T_A## and ##T_B## respectively, where ##T_{A} > T_{B}##. The tanks each have a heat capacity ##C##, and they are thermally isolated from their environment. Suppose that a heat engine is installed in contact with the...
  12. S

    Question about Reversible Engines and Carnot Efficiency

    Homework Statement I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. The highlighted parts of the image are where I am having some issues. I...
  13. L

    A question about diesel engines

    I have read ( excuse me but i don't remember the reference) that a diesel engine, contrary to an engine that works on the otto cycle, is a " steady torque" engine meaning that torque doesn't change with revolutions. Could someone explain me the reason? ( in case that this statement is true )...
  14. N

    Thermal efficiency of reciprocating engines

    In a perfect, ideal world with constant specific heats the thermal efficiency of an otto cycle is dependent on its pressure ratio and a diesel cycle is dependent on its pressure ratio and cut off ratio. But since in the real world the equations with these terms do not hold since specific heats...
  15. weerakkodi

    Marine Propulsion: 4 Engine-Fast Gunboat Not Achieving 20 Knots

    I have a some problem about marine propulsion. Assume the 4 engine-fast gunboat is moved by forward two engines. The boat get 10 knots. Then if other Aft two engines operate gradually. You know the boat doesn't get 20 knots speed. What are the reason for that? Explain theoretically? Thanks for...
  16. shanepitts

    Exploring the Limits of Heat Engines with Ice Expansion

    Noting that ice expands by about 9%, why isn't it possible ot build a heat engine from this natural process?
  17. N

    Regarding efficiency of heat engines

    I tried to calculate the efficiency of a engine using the formula : Efficiency = (Net Work Done) / (Heat absorbed) And then I tried to calculate the efficiency of respective Carnot engine by two ways : 1) Efficiency = (Net Work Done) / (Heat absorbed) 2) Efficiency = 1 - (Temperature Lowest /...
  18. person_random_normal

    Engines in Cars: Exploring the Carnot Cycle

    are engines in our cars follow the carnot cycle or they work differently
  19. T

    How Does the Universe Use Temperature Differences to Create Structures?

    The main result of thermodynamics is that if you have a place that is hot and another place that is colder, you can operate a heat engine by absorbing heat from the hot place and dumping it in the cold place, extracting some useful work in the process. It gives you a way to calculate the...
  20. Borek

    Computer games based on physics engines

    This is quite a serious question, I was asked to write few words about a similar game (not officially published yet) and I started to wonder what were the earlier programs of this type. This is partly engineering and partly physics problem. Many computer games use some kind of physics engines...
  21. J

    Thermodynamics - engines question

    I'm stuck on a question, part d below: My attempt: I reckon that T4 = T3 and T2 = T1, otherwise I don't know how else you can get T4 and T2...? Once I got first part of d, I reckon I could do efficiency using part c that I derived. I don't see where I'm supposed to use compression ratios...
  22. BonesSheppard

    Why buy new model rocket engines?

    Hi I was wondering why are model rocket engines disposable after one use? Is it because it is more economically feasible to buy a new model rocket engine than to repair a used one because the process of using a model rocket engine always ruins it? Also, if it is the case that model rocket...
  23. S

    Engines' aggragated technical data for a presentation

    Hi everyone! I am trying to make a presentation concerning up to date internal combustion engines for different applications (light duty/passenger cars, heavy duty, marine/low rpm, aviation etc). I don't need any charts just sheer numbers of power, capacity, weight, engine dimensions...
  24. T

    A rocket fires two engines simultaneously

    A rocket fires two engines simultaneously. One produces a thrust of 655N directly forward while the other gives a thrust of 508N at an angle 34.0∘ above the forward direction 1.Find the magnitude of the resultant force which these engines exert on the rocket. 2.Find the deviation of the...
  25. E

    Why must VTOL engines be larger than normal engines?

    I am studying to be a pilot and something I've read in the book confuses me. It is that Vertical Takeoff and Landing (VTOL) engines need to be heaver than their corresponding traditional takeoff/landing counterparts. Wikipedia says the same thing here. I am going to interpret "larger" and...
  26. V

    What is the Ideal System for Running a Nuclear-Powered Heat Engine in Space?

    (I'm not sure I put this thread in the right sub-forum) If we need to operate a nuclear-powered heat engine in space to run a generator, meaning it can only be cooled by radiation, what kind of system should we go for, if we want the power per unit mass ratio to be as high as possible? I've...
  27. T

    How to Calculate Steam Engine Efficiency and Water Usage in a Power Plant

    Homework Statement At a steam power plant, steam engines work in pairs, the heat output of the first one being the approximate heat input of the second. The operating temperatures of the first are 718∘C and 427∘C, and of the second 419∘C and 270∘C. A) If the heat of combustion of coal is...
  28. X

    Aluminum Engines: What Prevents Warping?

    Hello all, Most engines today in passenger cars are made out of aluminum instead of iron. I am confused about the fact that aluminum is lighter than cast iron and warps easier under extreme temperatures. How do they stop this warping from occurring?
  29. dean barry

    Calculating Cooling & Alternator Losses for Engines

    When dealing with power losses from engine to drive wheel(s) i ignored losses other than straight friction, can cooling and alternator losses be taken as roughly a percentage of the cars engine power ? Thanks Dean
  30. M

    Understanding the Carnot Cycle: Heat Pumps & Engines

    Greetings, Here is my thought process on the carnot cycle, regarding heat pumps and engines. I'd much appreciate it if you can clear up any misconceptions and answer my question at the very end. So my book states that there is no change in internal energy in a heat engine, but neither confirm...
  31. M

    Reciprocating Engines and Use of Vaccum

    Hi all, I have a random query that I suspect you guys will able to help me with on reciprocating engines (ala like steam engines rather than petrol motors). In the classic steam engines, obviously boiling water in a Pressure vessel and fed through a reciprocating engine is able to produce...
  32. M

    A question about search engines.

    Can you explain me why search engines sometimes can not find existing entries. I can find them in the site, I can see them but Google and Bing can not find them. Best Regards.
  33. A

    What are examples of high efficency engines?

    im looking for engines that are known for being extremely high effiency. im not just talking about high efficency consumer engines, but highest records, etc also, consumer level is nice as well, but please tell me that they are consumer level if you do list them. please list electric...
  34. A

    Reversible engines with different efficiencies

    Is is possible to have 2 different engines with all the following criterion? 1) Are reversible 2) Work differently (different cycles) 3) At the same working temepratures have different efficiencies. E.g. Working temperatures 100K and 50K. Engine 1: Carnot's Efficiency - 50%...
  35. V

    Small Displacement High RPM Engines

    I'm looking into buying an E34 530i with a smaller 3 liter V8 compared the the 540 4.4 liter V8. A lot of people online say buying a 530 is pointless when you can get the same car with more displacement and more power. I think that's ridiculous since displacement is only 1 of many ways to make...
  36. C

    Exploring Ford EcoBoost & Inline 6 Engines

    I've noticed that engines have gotten very complicated, thus more complicated in the past few years into squeeze more power and efficiency out of them, Ford's ecoboost in particular. I was wondering if it would be just as efficient to equip FWD cars with a small, very undersquare inline sixes...
  37. D

    Basic probability aeroplane engines problem

    Hi all, I've got a past paper question that goes something like this: An aeroplane has four engines. During a certain journey, each engine fails with a probability of 0.1, independantly of the others. The aeroplane can fly when at least two engines are working. Calculate: A) The...
  38. J

    Exploring the Limitations of Standard Diesel Engines

    this is thing I'm thinking about for few years. why standard passenger car diesel engines are so limited in engine capacities range? if we take petrol engines, there are anything from 1.0 liter to 3.0l Inline 4 cylinders, 2.0-4.0l 6 cylinders (or even bigger in USA), 4-7l V8 etc. but take...
  39. M

    Efficiency of Stirling heat engines

    Not sure if this should be posted in the general physics forums or in the hw/coursework section. I'm in my second semester of general physics and have to do a class project. For my project I built an alpha type Stirling engine. In the paper I need to write I need to explain how it works using...
  40. QuinnMcHugh

    Learning about and building engines

    Hi guys, I'm an incoming engineering student at Ohio State and am really fascinated with what goes on under the hood of my car. I've done about 20 minutes of fruitless light searching on how engines work and wanted to know if there are any classic textbooks or resources on this topic. Also, I'd...
  41. B

    Very Basic Thermodynamics, H20, and Jet Engines

    Dear Physics People, I am a religion teacher with a background in philosophy and theology. I haven't taken a physics or calculus in some years, so there is a lot of information that I'm missing in my head. So here's the deal. Airlines spend millions of dollars on fuel a day (around $32...
  42. J

    Automotive Alternative engines for a car?

    a friend and i have been discussing taking what we know (mostly what i know) in the field of mechanical engineering and designing and building a car.. it will be my car, but he's willing to help with it the body style of this car might look something like a cross between a corvette/viper and...
  43. A

    Should I add an intercooler and EGR to my turbocharged gas engine?

    Hey Guys needed some advice related to Turbocharging of natural gas engines. I'm working on turbocharging of gas engine for the first time and was trying to do some research on the same before jumping into the nitty gritty stuff. I Do not have much experience working with turbochargers. Turbo...
  44. S

    Temperature & Pressure at Exhaust of IC Engines

    what will be the temperature and pressure at the exhaust of IC engine?
  45. C

    Can Heat Engines Be Built? An Exploration

    Homework Statement a heat engine draws 200J of heat from the hot reservoir at 400K produces 110J of useful work and dumps 90J into the cold reservoir at 200K could this engine be built why or why not? Homework Equations PV=NkbT The Attempt at a Solution Not Sure on how I would set...
  46. B

    Heat engines and finding efficiency

    Hello, Homework Statement Engine A receives four times more input heat, produces six times more work, and rejects three times more heat than engine B. Find the efficiency of (a) engine A and (b) engine B. Homework Equations e = |W|/|QH| e = 1 - |Qc|/|QH| The Attempt at a...
  47. S

    Electrodynamic Combustion Control for Rocket Engines

    A company called ClearSign says it can use electric fields to shape combustion flames to improve powerplant efficiency by upto 30%: http://www.technologyreview.com/news/520466/flame-shaping-electric-fields-could-make-power-plants-cleaner/...
  48. C

    Why are gas turbine engines not used in automobiles?

    barring a few exceptions i read that it is because they aren't effecient at small scale. can someone elaborate on that? also, would even smaller turbines need some time to start up?
  49. D

    Why not use turbine engines in cars?

    Thank you for reading. Turbine engines have been used earlier by Chrysler. If throttle response is a reason they aren't prevalent there are many ways to reduce it. If I am not wrong, the compressor can have variable geometry vanes(similar to VGTs) and thereby reduce lag. I learned that it...
  50. D

    Lithium Hydride as energy source for Combustion Engines

    Lithium Hydride contains more hydrogen per unit volume than liquid hydrogen does, so what is stopping us from developing a Lithium Hydride storage solution to supply hydrogen to a vehicle's engine? The reactivity of the substance would throw up some substantial challenges, but compared to...
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