An interesting idea, and with a lot of merit. It will be fun to watch how this plays out. Control of the piston could be very tricky. Tom
Question for anyone who understands the engineering... I thought the reason why combustion engines are so inefficient is because of the waste heat they generate? Isn't that the chief advantage of a fuel-cell system, which is supposed to generate less waste heat? If that's true, I don't see how the free-piston engine can be more efficient than a fuel cell, considering that it will still generate a lot of waste heat.
I agree. At best, the free piston will not have the losses due to friction and such, but you still have heat losses. My guess is they'll be better than the conventional gasoline engine, but nowhere near as efficient as electricity.
My understanding is that conventional uses of ICEs, e.g., conventional cars, have large losses in the transmission. With this setup, you can get rid of the transmission by placing permanent magnets directly on the pistons. I don't know the exact factor, but transmissions in normal autos are sources of large power losses. You need the transmission to match the torque of the engine to what is required to turn the wheels since the torque from ICEs is not constant over the rotation rate of the engine. Electric motors have full torque from 0 rpm to their maximum rpm. This is why electric cars do not need a transmission and the lack of a transmission in an electric car is one of the reasons they are more efficient than ICE cars.
If this concept seems so promising, I'm suprised the LARGE utilities/energy companies haven't already experimented with this. They probably have, and decided to abandon the idea. Think about it ... it's been 88 years, and billions of dollars of electricity are generated every day - I'm sure the electric companies have already conducted experiments on this. Try it in your garage - hey, if you can make it work, then Awesome!!! It's because of the difference between an Isotherm and an Adiabat. Look up "Carnot Cycle" on Wikipedia. Yes, you are right that it is because of heat loss - but the Carnot Cycle explains HOW even more heat is lost. Long story short, when a gas expands, it loses heat, and additional heat must be supplied into the cylinder to counter that loss.
This basically looks like a double ended 2-stroke engine. Good power but not so good with the emissions.
I'm an engineer but not an automotive nor mechanical one. As for transmission losses, from what I've seen in magazines and having dynoed my former 02 Maxima, automatic transmission cars typically have about a 23-25% losses (in terms of hp measured at the wheels vs. rated crank hp). Manuals IIRC have 13-15% losses. Another problem is that I believe at lower vehicle speeds, overall car efficiency is terrible and while idle, you're getting 0 mpg. Also, non-hybrids have no means of recapturing any kinetic energy to be repurposed later to propel the car. I believe two huge sources of inefficiency in IC engines is internal friction from the pistons and bearings along w/the combustion itself. Combustion of the air and gasoline mixture produces a HUGE amount of waste heat which cars currently have no means of converting into any useful energy to propel the car nor running any of its electrical systems. update: I re-found these two URLs that relate to the questions posed here. Advanced Technologies & Energy Efficiency Tesla Motors - well-to-wheel
Free Piston Power Pack The FP3 is a most efficient, low cost, elegant electric generator module of exceptional power density. Operation is based on 'free pistons' (unrestrained by con-rods or crank shaft) being driven back and forth inside cylinders by controlled internal combustion. Permanent magnets are attached to these pistons and move through stator coils, thus generating electric power. Compression ratio and stroke, as well as exhaust valve timing and lift, are software controlled rather than through conventional mechanical means. The result is mechanical simplicity, unequalled efficiency and extremely low harmful emissions. (Figure 1: 100kW generator module) Salient features of a 100kW FP3 module: Size: 660x280x280mm Mass: 100kg Two-stroke operation Integral charge compressor Power Density: 1kW/kg; 2 kW/litre Fuelled by Gasoline, Diesel (Bio, JP8), LPG, Ethanol, Hydrogen, etc. Direct, high pressure fuel injection Variable exhaust valve lift and timing Variable compression ratio and stroke Mechanical simplicity (software ‘replaces’ conventional con-rods, cam and crankshaft) Readily scalable from 25 to 500kW output power Efficiency 50% What problem does our technology solve? The FP3 has the potential to make a greater single contribution to the reduction of greenhouse gas emissions than any other technology currently available. Installed in a Series Hybrid Electric vehicle, it offers a significant reduction in fuel consumption and harmful emissions when compared with a conventional power train. It provides a means for oil to continue to be the primary automotive energy source but in an economically viable and environmentally responsible manner. The FP3 is a sterling solution to the land transportation fossil fuel waste-and-pollution conundrum. Primary Application The exceptional power density of the FP3 makes it possible to construct a Series Hybrid Electric Motor Vehicle capable of regenerating, storing and subsequently re-using the kinetic energy, presently wasted, when slowing down and braking. This is achieved without any compromise in vehicle mass, performance, handling and payload capacity. The up-shot is a substantial reduction in fuel consumption and harmful emissions.
One thing to also to note, fuel cells are hardly 100% efficient end all be all of energy production, as your efficiency is directly related to how much power is being drawn and for something large like a car that could significantly put a dent in the efficiency... IIRC fuel cells are in the range of being about 40% efficient for cars if you ignore the cost of making the fuel... which granted is quite a bit more than an ICE but still is a very reachable goal to beat.
Also remember that fuel cells need to run at a more or less constant level of output. This means that fuel cells are almost always buffered by a bank of batteries, which in turn add losses to the system. Tom
Don't extrapolate the characteristics of a weed eater or outboard engine to all two stroke engines. The pollution from a little two stroke is from two major sources: oil in the gasoline for lubrication and unburned gasoline blowing through during the scavenge cycle. Lubricate the engine without oiling the gas, and one source goes away. Do direct injection of fuel after the exhaust is closed and the unburned gas bypass is gone. Large locomotive and ship engines are two stroke also, and are every bit as clean as the four stroke engines. I could write a long story about the management of electromotive, the worlds biggest maker of locomotives, believing that "two strokes are dirty" and spending millions that they didn't need too. They staffed up a whole new design group to develop a new four stroke from the ground up... not believing their own designers when they said they could meet Tier II with the two stroke design. End the end, the two stroke guys came through with their promise. They fielded a few of the new four stroke engines and all were duds that had to be recalled and replaced with two strokes. The newest two strokes don't ever produce visible smoke, they don't even smell like a diesel.
