|
It looks like a fun project, but needlessly heavy and complicated for the small improvements.
What we're really trying to do is, after the nice high-quality heat has already been harnessed by the pistons, find a way to squeeze a little more energy out of the waste heat that is left over, particularly at part-power conditions. There are ALWAYS ways to squeeze out a bit more energy; the problem is the smaller the temperature difference available, the bigger the device squeezing the heat out of the fluid needs to be for a given amount of power.
This makes the challenge as follows: find a way to squeeze energy out of waste heat with minimal growth in weight and complexity. I see a few ways to do this that would be superior to the steam system.
1) Turbo alternator. Turbochargers work by squeezing waste heat out of exhaust. While cruising, we open the wastegate and they basically sit there not doing much of anything. Why not gear an alternator to the turbo and use it to charge a battery? Particularly on a hybrid system, this power could be fed to an electric motor. On a nonhybrid, perhaps there could just be a small motor-generator (like a robust starter motor mild-hybrid system) to add power to the crankshaft. When high power is demanded, the turbo alternator becomes a motor and quickly spins up the compressor on the turbocharger, dramatically reducing lag. Of course, this would require some way to decouple the compressor from the turbine. Perhaps pairing this with an electric supercharger would be best.
2) Control power by controling valve duration and going into a deep Atkinson cycle. Valvetronic already does this to a very small degree, but MUCH more needs to be done.
An Atkinson cycle engine has a short intake stroke and a long power stroke. This longer power stroke give a longer expansion ratio, and more energy is extracted from the hot gases inside. While the original Atkinson cycle engines used a complicated linkage to do this, you can achieve a similar affect on a normal engine through controlling the intake valves. Hybrids, like the Prius, run on an Atkinson cycle. They intake a full cylinder of air, but as the piston starts coming up for the compression stroke, it keeps the intake valve open for a bit, puking some of the air back out into the intake. The rest of the stroke operates normally. Of course, this lowers the effective displacement of the engine, so it sacrifices power if you run this way all the time. It would be even better if we could just shut the intake valve early because we wouldn't be pumping air back and forth across the intake valve.
If you could find a way to vary the valve duration across a very big range, you could control the power output of the engine this way. Part throttle crusing would become VERY efficient. When you needed full power, it would intake a full charge of air.
3) Ethanol and Super high compression ratios. Corn based biofuels are a farse, but ethanol has the benefit of being VERY high octane. A fuels highest octane rating is only needed for that brief time where lots of torque is demanded and cylinder pressures are very high. I propose, essentially, a factory meth system. This would allow you to run very high compression ratios, increasing efficiency and power, or you could also run very high boost levels. Ford is actually working on something like this.
All three of these ideas could be implemented at once with only small cost and weigh increases compared to any other turbo engine, and all accomplish the same goal of extracting more heat energy. The only new tech would be the valve lift control for Atkinson power control, and much of that could be adapted from existing tech like Valvetronic or Fiat Multiair.
|