--- "Stephen A. Lawrence" wrote: > As you pointed out, the diesel develops quite a bit of torque at low RPMs, which is useful in a conventional engine/transmission arrangement. It's irrelevant, however, if you're using a motor/generator/wheel-motor arrangement.
Not really. You absolutely need to compress air to a high ratio, and turbines are terribly inefficient for that, especially in the smaller sizes. In contrast, the torque of a diesel can drive an efficient scroll or Roots compressor to supply pressurized air for fully double the efficiency of a small turbine (like the Allison) and one tenth the cost of all those investment-cast blades. This is a major consideration ! as pressurized-air is the #1 major loss-item for small turbine design. > And if you want maximum power per pound from your motor... What's the diesel doing for you? It cools and pressure-reduces the exhaust a lot in the course of spinning itself. What's the point? The diesel-turbine-hybrid, which I am describing has two gigantic advantages over the pure turbine for smaller output engines. And remember this general point - pressure - and only pressure drives any turbine and high heat is needed ONLY for complete combustion - although admittedly the relationship with between heat and pressure is linear in THAT engine design only (pure turbine). The cooler exhaust of the diesel-hybrid, as mentioned, can be reheated using some air-bleed from the supercharger and some very small amount of added fuel, so that "lower heat" is a really a non-issue anyway ... BUT ... in the hybrid you will not need superalloys, as with a pure turbine, nor will you need the 2400 degree F. heat, in order to get a complete burn. Because the diesel operates at high compression ratios which are **unobtainable** with any practical turbine, you get complete fuel combustion but at far lower effective temperature and *complete burn* is what it is this (maximum efficiency) is all about. Plus -- pure turbines are not *scalable* downward without major losses in efficiency. And even if this hybrid is not as light in weight as a pure turbine, it is still a third the weight of a normal ICE like the Prius, when producing the same power. Thus the title of the post (referring to the power law) - which title, once again got lost in cyberspace. ...even Toyota acknowledges that they would use a smaller engine except for "marketing concerns" (the consumer thinks that they need to have "reserve power" available, even if it is seldom used. go figure.) Jones
