h a l f b a k e r ycarpe demi
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I've been wondering vaguely for a while about whether there might be more efficient ways of getting energy out of an internal combustion engine than the 'make pistons turn the crankshaft' model we all know and love.
In particular with the move towards indirect power ... using the engine to generate
electricity, and then using that electricity to drive the motor.
Idea here is avoid the rotary motion completely.
Build a flat bed, made up of horizontally opposed twin cylinders, each containing a double-headed piston.
Each piston could be made up almost entirely of a massively wound coil of suitable metal (extremely rigid and heat tolerant, while also extremely conductive). The engine block is made (largely) of a single block of magnetic metal, and there is some (wavy magic) way of maintaining a high current connection to each piston.
As the fuel explodes in one chamber, it pushes the piston down to the other end of the 'twin cylinder', compressing the air/fuel mixture down to blast point, and creating a vacuum at the other end, pulling in more fuel and air (nothing new there, then!). The same process then fires in reverse.
You have a rapidly oscillating coil in a high strength, concentrated magnetic field, generating a significant (?) alternating current from each cylinder pair.
Because no external mechanical connections are required you have far fewer moving parts, far less layout complexity, etc.
You could build engines made with just one big piston, or with massive arrays of tiny ones, depending on what provides the most efficient outcomes. And you can have them in any alignments, so that you can make the engine any shape.
Even better, there is no inertial mass on the system if pistons are not firing, so you can shut down any pistons which are not currently required, and fire them up again as you need more power.
The direct generation from the shuttling pistons would of course only provide the first order power outputs. You would also take the fast moving input and output airstreams (and any unburnt fuel) to add a number of turbines etc. Additionally, you would have quite a lot of waste heat to capture ...
Not sure what the best fuels would be, or how efficient something like this could be overall??
Generator-Only Mode
http://www.rasertec...s-phev-drive-system
The combustion engine is connected only to the electric generator and is not connected to the drive system. The engine is used only generate electricity and recharge the batteries [kindachewy, Jul 10 2009]
One of these then
http://en.wikipedia.../Free-piston_engine
"free piston generator" section [FlyingToaster, Jul 14 2009]
[link]
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I presume that the power profile would be relatively square, and would need some shaping, but this could be addressed via timing the various cylinders to generate power at slighlty varying times? |
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1)I'll bun this idea if you indicate the efficient way you intend to capture that waste heat. Then I'll strap it to a conventional ICE. |
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T2)his idea would be less efficient than a conventional mechanical system due to the fact that any time you translate from mechanical to electrical and back you waste. WASTE HEAT. |
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Thermodynamics Thermodynamics Thermodynamics |
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Yes, but there ARE vehicles which have ICE engines solely to act as generators, and which only drive via electric power. So you are going to have mechanical -> electrical -> mechanical. |
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The question is ... if you are going to do that, which is better - a conventional piston -> crankshaft -> rotating coil or this linear motion version? |
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Would your answer to the above still hold true if you wanted to optimise for variable power, with the engine often operating at small fractions of required peak power? |
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If I have a normal crankshaft engine operating at low power, it still needs to move a lot of its own heavy mass for each revolution. |
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I could (theoretically) have 100 very small pistons in my TCPS engine for when I want peak power. For minimum power, I could select to use only one of them -> the remaining 99 would all be at rest and consuming no energy. |
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they're called "free piston" engines... great idea but sadly not baked properly yet. My idea for controlling them involves varying the generator load to accomodate over/underpressure combustions. |
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heavy pistons, heavy windings, bulky conventional induction fuel and exhaust systems, heavy batteries, additional electric motors. It all ends up pretty pointless. Use an ultra light car with a de-rated conventional power plant and you will be able to, slowly, beat any non-plugin hybrid power plant currently available. |
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a free-piston engine is by definition pretty darn light. I don't agree with [kc]'s interpretation (many small pistons), preferring just 2 big'uns that you turn on whenever your cap-pack runs low. |
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I don't see why the pistons would be any heavier than normal ones - and this idea specifies making the piston (which you need anyway) as the coil, thus removing the need for extra weight of an additional coil. |
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My thinking towards this kind of combustion-generated electric drive was driven by wanting an ultra-flexible layout, allowing (for instance) massive ground clearance for 4x4 applications, or (for instance) very low centre of gravity and maximised use of inter-wheel space ... both of these requirements call for removal of any fixed drive trains, axles, etc. |
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The great thing about electricity is you can send it where you want it over lightweight, flexible wires - saving space, weight and (some) energy loss associated with traditional drivetrains and opening up all kinds of radical body plans and capabilities. |
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My currently preferred layout has individual (relatively small) electric motors in each wheel hub, each driving its own wheel directly via a continuously variable gearing system which is based on moving the point at which force is applied closer to the hub or closer to the rim. |
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Each wheel is mounted on a swing arm, with variable height suspension, rotatability of the assembly relative to the vehicle chassis, and independent steering (hub centred?) -> this allows full variability of ride height, body angle (front/back, and side/side), and wheelbase width/length |
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For me, even if combustion-generated electric drive is not necessarily the most efficient, this is paid for by the additional flexibility which wires-based transmission affords. |
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Meantime the loss of driveshaft etc helps offset the extra weight of the batteries & electric motors. |
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//waste heat// I'm no expert, but the halfbakery is full of heatpumps, heatsinks, Stirling engines and all kinds of other fancy stuff. I would think it should be fairly easy to use the heat differences within the coolant system to generate some power. |
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You maybe wouldn't get enough additional power to make much difference to a conventional ICE, which needs to use that power as it generates it ... but it could be valuable as an additional trickle charge effect that gradually builds up to useful levels. |
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Similarly with other sources that provide energy just when you don't need it, or at low power densities, and are therefore close to useless in a traditional engine, but great in an electric drive ... including induction braking and wind resistance (when decelerating), solar - (even when parked up) - and mains plug-in elements |
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You'd have a maximum efficiency ICE>gen>motor>wheels of 80'ish percent. Dunno what the efficiency of a direct drivetrain ICE>clutch>tranny>differential is. |
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in terms of energy transmission the best transverse FWD setups can make better than 80% to the wheels. Generally speaking for maximum fuel economy cruising the ICE on its own is really really hard to beat if it is designed for that application. A 1976 honda 1200 five speed made 46 mpg with a simple 8v engine and a crude 2bbl carburetor. On the highway I got consistently better than 50 mpg driving 55-60 mph. |
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//better than 80% to the wheels//
so not like 85 or 90% ? Sounds like power-by-wire has a good shot, especially with a cap-bank in the middle somewhere (100'ish pct) |
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ok and the Honda Insight? About the same and thirty years of technology behind it. The insight is safer, marginally faster, and far more expensive, so where exactly is the benefit of hybridization? In short it allows an underpowered car to behave somewhat like the same car with a more powerful engine. |
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