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I am trying to design a theoretical internal combustion (IC) engine. The ultimate goal is to achieve 3000 hp with this engine, for which I know I will need low bore x stroke ratio, high compression, direct injection, and 4 valves/cylinder. I am getting confused in my calculations, as the different dimensions are interrelated. How can I determine the optimal bore and stroke for this theoretical engine?

closed as too broad by JoErNanO, Chenmunka, Nick C, Shobin P, Sam Jun 28 '16 at 10:14

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    Naturally aspirated or boosted? – tlhIngan Jun 28 '16 at 6:49
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    What's your thermal efficiency? – tlhIngan Jun 28 '16 at 6:49
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    Let us know a bit more. What is the purpose of an engine (race or submarine)? What fuel type? Do you actually want to build it up and spend millions on developments or just CAD design? – Arturs Bolsunovskis Jun 28 '16 at 10:12
  • Thank you sir, i need more details about the startup. I thought that i have to start from the bore of cylinder. still i am having doubt on that, i studied a lot things what i want to do in the engine, but i am having more starting trouble, because the things which i have seen are looped together. The requirements are Low bore to stroke ratio, high compression ratio, startified DI, 4 valves/cylinder. by these things i can create more power fuel, high performable ic engine, but the calculations makes me more confused. I need more help sir – Elambharathi Jun 28 '16 at 11:24
  • Motorcycle engine 1340cc 4 cylinder with a bore 81mm and stroke 65mm and 12.5:1 compression ratio produces about 190 BHP, so 81 x 65 @ 12.5:1 gives 47.5 BHP. If it is naturally aspirated standard non-competition engine. If you supercharge it you can get about 350 BHP, but it will need better con-rods, pistons, clutch, oil pressure, etc. So for a reliable engine the will not cost you the most expensive headbolts, rods, pistons and one day blow it all into the sky, you might need to design a 10 liter twin boosted or supercharged engine. Decide how many cylinders you want.. – Arturs Bolsunovskis Jun 28 '16 at 14:08
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This looks like your first posting with Motor Vehicle maintenance and repair site. It looks like you are an engineering student, looking at a possible school project. Is that right? Welcome to the stackexchange!

You have a whole lot of decisions to make.

  1. First Choice: Type of engine? I'm going to assume you want an internal combustion engine. Choices here are

    • Gasoline Two Cycle Internal Combustion
    • Gasoline Four Cycle Internal Combustion
    • Diesel Reciprocating engine Internal Combustion
    • Wankel Internal Combustion
    • Jet Turbine Internal Combustion
    • External Combustion Sterling Engine

There are other designs out there, but these are the most common.

  1. Next step is to determine your power requirements. You've stated you wanted 3000 HP. Awesome.

  2. Next comes materials. What foundry do you have available? What materials are you thinking about? Do you have good feel for heat treat requirements? Do you have machine shops ready to go to advise you whats acceptable for their processes?

  3. Next step is to try to size the engine (for displacement style engines.) How much displacement total do you need? What pressures are we talking? (what are your safety & durability goals?) Use the appropriate thermodynamic tables for your choice of engine style to figure out what's possible for your designated fuel type. Obviously you will use the Otto Cycle for gasoline engine. Obviously this is where you need to proveout intake pressure stuff. Are you going to add boost? How are you planning on doing that?

  4. After you figure out displacement (total) then you can figure out number of cylinders, size of pistons and crankshaft throw. I will say there is a lot of published stuff out there that talks about this step a bit, particularly with regards to RPM range and torque. You didn't mention your targets for those.

  5. At some point in time you should probably evaluate not only the number of cylinders, but also how they are arranged. How big a deal is vibration to you? Are you going inline block, V block, Horizontal opposing or perhaps an alternative design? Are you going to be adding a counterbalance shaft?

  6. And here is a hard one.. How are you going to control the intake and exhaust on your engine? two valves per cylinder? Three? Four or more? Perhaps you have an alternative design in mind. Again, awesome. How are you going to control the opening and closing of each valve? How are you going to transmit the energy to do that? Are you going with valve springs or a desmodromic valve design.

  7. You should also take a moment to ensure you've accommodate your design for heat loss too. Radiator control? coolant? Thermostat? Coolant pump? The sky is the limit.

  8. Onward to lubrication. Don't forget you've got to provide lubrication to all the moving parts within your engine. I'm assuming you are going to be cross drilling and welding up the access holes in your crankshaft. That's tough on heat treat design, but that's what makes engineering so interesting, no?

  9. Now is a good time to figure out exactly the details on mixing fuel and air. Are you going carburator? Hi pressure injectors? Mechanical or electric fuel pump? control system? Calibration? What sensors will you need for your integrated system.

  10. Oooh, I almost forgot. What specifications are you meeting for emissions? current legal requirements? How are you going to control that stuff?

  11. About this time you should probably be placing all of your designs in a 3D CAD system. A system that integrates well for finite element analysis will save you time. Its at this point you can begin to determine material requirements, including all heat treat. The goal is to create a model good enough to perform a cost analysis on your 3000 hp motor. You didn't say.. what is your budget for this thing? Are you just making one, or a whole bunch of these. If you can make the thing fit into a package say 20" x 20" x 30" I'm guessing you'll have a great market for sales. Again, Awesome. Oh.. and don't forget we're all going to need complete dimensional analysis to know how tight the tolerances are on ALL the parts in the system. Can't quote the job without that.

  12. Actually as I look at this list, the displacement and # of cylinders necessary seems kind of a minor decision. Is that really where you want to start the journey? I guess that's okay, its your project.

Let us know how this turns out. I will say, it does seem like a whole lot to tackle at once. Good luck with it. And if you want help, I'm offering. I did spend nearly 30 years as an automotive design engineer (plus other jobs) at a Detroit based manufacturer. My email address is attached to my profile.

  • Thank you sit, i need more details about the startup. I thought that i have to start from the bore of cylinder. still i am having doubt on that, i studied a lot things what i want to do in the engine, but i am having more starting trouble, because the things which i have seen are looped together. The requirements are Low bore to stroke ratio, high compression ratio, startified DI, 4 valves/cylinder. by these things i can create more power fuel, high performable ic engine, but the calculations makes me more confused. I need more help sir. – Elambharathi Jun 28 '16 at 10:03

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